1
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Alonso-del Valle A, Toribio-Celestino L, Quirant A, Pi CT, DelaFuente J, Canton R, Rocha EPC, Ubeda C, Peña-Miller R, San Millan A. Antimicrobial resistance level and conjugation permissiveness shape plasmid distribution in clinical enterobacteria. Proc Natl Acad Sci U S A 2023; 120:e2314135120. [PMID: 38096417 PMCID: PMC10741383 DOI: 10.1073/pnas.2314135120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2023] [Accepted: 10/26/2023] [Indexed: 12/18/2023] Open
Abstract
Conjugative plasmids play a key role in the dissemination of antimicrobial resistance (AMR) genes across bacterial pathogens. AMR plasmids are widespread in clinical settings, but their distribution is not random, and certain associations between plasmids and bacterial clones are particularly successful. For example, the globally spread carbapenem resistance plasmid pOXA-48 can use a wide range of enterobacterial species as hosts, but it is usually associated with a small number of specific Klebsiella pneumoniae clones. These successful associations represent an important threat for hospitalized patients. However, knowledge remains limited about the factors determining AMR plasmid distribution in clinically relevant bacteria. Here, we combined in vitro and in vivo experimental approaches to analyze pOXA-48-associated AMR levels and conjugation dynamics in a collection of wild-type enterobacterial strains isolated from hospitalized patients. Our results revealed significant variability in these traits across different bacterial hosts, with Klebsiella spp. strains showing higher pOXA-48-mediated AMR and conjugation frequencies than Escherichia coli strains. Using experimentally determined parameters, we developed a simple mathematical model to interrogate the contribution of AMR levels and conjugation permissiveness to plasmid distribution in bacterial communities. The simulations revealed that a small subset of clones, combining high AMR levels and conjugation permissiveness, play a critical role in stabilizing the plasmid in different polyclonal microbial communities. These results help to explain the preferential association of plasmid pOXA-48 with K. pneumoniae clones in clinical settings. More generally, our study reveals that species- and strain-specific variability in plasmid-associated phenotypes shape AMR evolution in clinically relevant bacterial communities.
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Affiliation(s)
- Aida Alonso-del Valle
- Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, Madrid28049, Spain
| | - Laura Toribio-Celestino
- Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, Madrid28049, Spain
| | - Anna Quirant
- Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana, Valencia46020, Spain
| | - Carles Tardio Pi
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca62209, México
- Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas, Unidad Académica Yucatán, Universidad Nacional Autónoma de México, Yucatán04510, México
| | - Javier DelaFuente
- Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, Madrid28049, Spain
| | - Rafael Canton
- Servicio de Microbiología, Hospital Universitario Ramón y Cajal-Instituto Ramon y Cajal de Investigacion Sanitaria, Madrid28034, Spain
- Centro de Investigación Biológica en Red de Enfermedades Infecciosas, Instituto de Salud Carlos III, Madrid28029, Spain
| | - Eduardo P. C. Rocha
- Institut Pasteur, Université de Paris Cité, CNRS UMR3525, Microbial Evolutionary Genomics, Paris75015, France
| | - Carles Ubeda
- Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana, Valencia46020, Spain
- Centro de Investigación Biológica en Red de Epidemiología y Salud Pública, Instituto de Salud Carlos III, Madrid28029, Spain
| | - Rafael Peña-Miller
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca62209, México
| | - Alvaro San Millan
- Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, Madrid28049, Spain
- Centro de Investigación Biológica en Red de Epidemiología y Salud Pública, Instituto de Salud Carlos III, Madrid28029, Spain
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2
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Dewan I, Uecker H. A mathematician's guide to plasmids: an introduction to plasmid biology for modellers. MICROBIOLOGY (READING, ENGLAND) 2023; 169:001362. [PMID: 37505810 PMCID: PMC10433428 DOI: 10.1099/mic.0.001362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2023] [Accepted: 07/03/2023] [Indexed: 07/29/2023]
Abstract
Plasmids, extrachromosomal DNA molecules commonly found in bacterial and archaeal cells, play an important role in bacterial genetics and evolution. Our understanding of plasmid biology has been furthered greatly by the development of mathematical models, and there are many questions about plasmids that models would be useful in answering. In this review, we present an introductory, yet comprehensive, overview of the biology of plasmids suitable for modellers unfamiliar with plasmids who want to get up to speed and to begin working on plasmid-related models. In addition to reviewing the diversity of plasmids and the genes they carry, their key physiological functions, and interactions between plasmid and host, we also highlight selected plasmid topics that may be of particular interest to modellers and areas where there is a particular need for theoretical development. The world of plasmids holds a great variety of subjects that will interest mathematical biologists, and introducing new modellers to the subject will help to expand the existing body of plasmid theory.
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Affiliation(s)
- Ian Dewan
- Research Group Stochastic Evolutionary Dynamics, Department of Theoretical Biology, Max Planck Institute for Evolutionary Biology, Plön, Germany
| | - Hildegard Uecker
- Research Group Stochastic Evolutionary Dynamics, Department of Theoretical Biology, Max Planck Institute for Evolutionary Biology, Plön, Germany
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3
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Ma Y, Ramoneda J, Johnson DR. Timing of antibiotic administration determines the spread of plasmid-encoded antibiotic resistance during microbial range expansion. Nat Commun 2023; 14:3530. [PMID: 37316482 DOI: 10.1038/s41467-023-39354-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Accepted: 06/08/2023] [Indexed: 06/16/2023] Open
Abstract
Plasmids are the main vector by which antibiotic resistance is transferred between bacterial cells within surface-associated communities. In this study, we ask whether there is an optimal time to administer antibiotics to minimize plasmid spread in new bacterial genotypes during community expansion across surfaces. We address this question using consortia of Pseudomonas stutzeri strains, where one is an antibiotic resistance-encoding plasmid donor and the other a potential recipient. We allowed the strains to co-expand across a surface and administered antibiotics at different times. We find that plasmid transfer and transconjugant proliferation have unimodal relationships with the timing of antibiotic administration, where they reach maxima at intermediate times. These unimodal relationships result from the interplay between the probabilities of plasmid transfer and loss. Our study provides mechanistic insights into the transfer and proliferation of antibiotic resistance-encoding plasmids within microbial communities and identifies the timing of antibiotic administration as an important determinant.
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Affiliation(s)
- Yinyin Ma
- Department of Environmental Microbiology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), 8600, Dübendorf, Switzerland.
- Department of Environmental Systems Science, Swiss Federal Institute of Technology (ETH), 8092, Zürich, Switzerland.
| | - Josep Ramoneda
- Department of Environmental Microbiology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), 8600, Dübendorf, Switzerland
- Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, 80309, USA
| | - David R Johnson
- Department of Environmental Microbiology, Swiss Federal Institute of Aquatic Science and Technology (Eawag), 8600, Dübendorf, Switzerland.
- Institute of Ecology and Evolution, University of Bern, 3012, Bern, Switzerland.
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4
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Fahy S, O’Connor JA, Lucey B, Sleator RD. Hospital Reservoirs of Multidrug Resistant Acinetobacter Species-The Elephant in the Room! Br J Biomed Sci 2023; 80:11098. [PMID: 37020476 PMCID: PMC10069268 DOI: 10.3389/bjbs.2023.11098] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 03/09/2023] [Indexed: 04/07/2023]
Abstract
Environmental contamination is estimated to contribute to up to 20% of all hospital acquired infections. Acinetobacter baumannii is an example of one the most prevalent opportunistic pathogens causing severe and persistent infections in immunocompromised patients. It has proven ability to form biofilms, has significant associated multi-drug resistance and is able to transfer mobile genetic elements to other clinically relevant pathogens. All of these factors point to a definite utility of A. baumannii as an indicator organism for effectiveness of decontamination regimens as well as environmental screening. There is an increased cost, both financial and clinical, associated with multi drug resistant organisms, carbapenem resistant A. baumannii. With a dearth of new antimicrobials in development, now is the time to radically transform and lead the introduction of scientifically based environmental screening and microbiological verified decontamination to control the dissemination of further resistance.
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Affiliation(s)
- S. Fahy
- Department of Clinical Microbiology, Mercy University Hospital, Cork, Ireland
- Department of Biological Sciences, Munster Technological University, Cork, Ireland
| | - J. A. O’Connor
- Department of Biological Sciences, Munster Technological University, Cork, Ireland
| | - B. Lucey
- Department of Biological Sciences, Munster Technological University, Cork, Ireland
- *Correspondence: B. Lucey,
| | - R. D. Sleator
- Department of Biological Sciences, Munster Technological University, Cork, Ireland
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5
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Haudiquet M, de Sousa JM, Touchon M, Rocha EPC. Selfish, promiscuous and sometimes useful: how mobile genetic elements drive horizontal gene transfer in microbial populations. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210234. [PMID: 35989606 PMCID: PMC9393566 DOI: 10.1098/rstb.2021.0234] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Horizontal gene transfer (HGT) drives microbial adaptation but is often under the control of mobile genetic elements (MGEs) whose interests are not necessarily aligned with those of their hosts. In general, transfer is costly to the donor cell while potentially beneficial to the recipients. The diversity and plasticity of cell–MGEs interactions, and those among MGEs, result in complex evolutionary processes where the source, or even the existence of selection for maintaining a function in the genome, is often unclear. For example, MGE-driven HGT depends on cell envelope structures and defense systems, but many of these are transferred by MGEs themselves. MGEs can spur periods of intense gene transfer by increasing their own rates of horizontal transmission upon communicating, eavesdropping, or sensing the environment and the host physiology. This may result in high-frequency transfer of host genes unrelated to the MGE. Here, we review how MGEs drive HGT and how their transfer mechanisms, selective pressures and genomic traits affect gene flow, and therefore adaptation, in microbial populations. The encoding of many adaptive niche-defining microbial traits in MGEs means that intragenomic conflicts and alliances between cells and their MGEs are key to microbial functional diversification. This article is part of a discussion meeting issue ‘Genomic population structures of microbial pathogens’.
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Affiliation(s)
- Matthieu Haudiquet
- Institut Pasteur, Université de Paris Cité, CNRS UMR3525, Microbial Evolutionary Genomics, Paris 75015, France
| | - Jorge Moura de Sousa
- Institut Pasteur, Université de Paris Cité, CNRS UMR3525, Microbial Evolutionary Genomics, Paris 75015, France
| | - Marie Touchon
- Institut Pasteur, Université de Paris Cité, CNRS UMR3525, Microbial Evolutionary Genomics, Paris 75015, France
| | - Eduardo P C Rocha
- Institut Pasteur, Université de Paris Cité, CNRS UMR3525, Microbial Evolutionary Genomics, Paris 75015, France
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6
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Dimitriu T. Evolution of horizontal transmission in antimicrobial resistance plasmids. MICROBIOLOGY (READING, ENGLAND) 2022; 168. [PMID: 35849537 DOI: 10.1099/mic.0.001214] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Mobile genetic elements (MGEs) are one of the main vectors for the spread of antimicrobial resistance (AMR) across bacteria, due to their ability to move horizontally between bacterial lineages. Horizontal transmission of AMR can increase AMR prevalence at multiple scales, from increasing the prevalence of infections by resistant bacteria to pathogen epidemics and worldwide spread of AMR across species. Among MGEs, conjugative plasmids are the main contributors to the spread of AMR. This review discusses the selective pressures acting on MGEs and their hosts to promote or limit the horizontal transmission of MGEs, the mechanisms by which transmission rates can evolve, and their implications for limiting the spread of AMR, with a focus on AMR plasmids.
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7
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Fitness effects of plasmids shape the structure of bacteria-plasmid interaction networks. Proc Natl Acad Sci U S A 2022; 119:e2118361119. [PMID: 35613058 PMCID: PMC9295774 DOI: 10.1073/pnas.2118361119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SignificanceAntimicrobial resistance (AMR) poses a great challenge for modern medicine. Plasmids are important vectors of antibiotic resistance genes. Plasmids can have context-dependent effects on their hosts, generally slowing their growth rate but also providing protection from specific antibiotics and heavy metals. Thus, models that predict population densities based on interactions between species are useful for explaining plasmid dynamics. Here, we predict with a simple ecological model the properties of a host (e.g., bacteria) and symbiont (e.g., plasmid) interaction network. Using experimental microbial communities and a conjugative plasmid, we confirm our predictions that beneficial symbionts spread more widely through a microbial community and provide key experimental results for network ecologists seeking to uncover the determinants of ecological network structure.
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8
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Pinilla-Redondo R, Russel J, Mayo-Muñoz D, Shah SA, Garrett RA, Nesme J, Madsen JS, Fineran PC, Sørensen SJ. CRISPR-Cas systems are widespread accessory elements across bacterial and archaeal plasmids. Nucleic Acids Res 2022; 50:4315-4328. [PMID: 34606604 DOI: 10.1093/nar/gkab859/40506127/gkab859.pdf] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 09/08/2021] [Accepted: 10/02/2021] [Indexed: 05/27/2023] Open
Abstract
Many prokaryotes encode CRISPR-Cas systems as immune protection against mobile genetic elements (MGEs), yet a number of MGEs also harbor CRISPR-Cas components. With a few exceptions, CRISPR-Cas loci encoded on MGEs are uncharted and a comprehensive analysis of their distribution, prevalence, diversity, and function is lacking. Here, we systematically investigated CRISPR-Cas loci across the largest curated collection of natural bacterial and archaeal plasmids. CRISPR-Cas loci are widely but heterogeneously distributed across plasmids and, in comparison to host chromosomes, their mean prevalence per Mbp is higher and their distribution is distinct. Furthermore, the spacer content of plasmid CRISPRs exhibits a strong targeting bias towards other plasmids, while chromosomal arrays are enriched with virus-targeting spacers. These contrasting targeting preferences highlight the genetic independence of plasmids and suggest a major role for mediating plasmid-plasmid conflicts. Altogether, CRISPR-Cas are frequent accessory components of many plasmids, which is an overlooked phenomenon that possibly facilitates their dissemination across microbiomes.
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Affiliation(s)
- Rafael Pinilla-Redondo
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
- Department of Technological Educations, University College Copenhagen, Sigurdsgade 26, 2200 Copenhagen, Denmark
| | - Jakob Russel
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
| | - David Mayo-Muñoz
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Shiraz A Shah
- Copenhagen Prospective Studies on Asthma in Childhood (COPSAC), Herlev and Gentofte Hospital, University of Copenhagen, Ledreborg Alle 34, 2820 Gentofte, Denmark
| | - Roger A Garrett
- Danish Archaea Centre, Department of Biology, University of Copenhagen, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen, Denmark
| | - Joseph Nesme
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
| | - Jonas S Madsen
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
| | - Peter C Fineran
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
- Bio-Protection Research Centre, University of Otago, Dunedin, New Zealand
| | - Søren J Sørensen
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
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9
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Jamieson-Lane AD, Blasius B. The gossip paradox: Why do bacteria share genes? MATHEMATICAL BIOSCIENCES AND ENGINEERING : MBE 2022; 19:5482-5508. [PMID: 35603365 DOI: 10.3934/mbe.2022257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Bacteria, in contrast to eukaryotic cells, contain two types of genes: chromosomal genes that are fixed to the cell, and plasmids, smaller loops of DNA capable of being passed from one cell to another. The sharing of plasmid genes between individual bacteria and between bacterial lineages has contributed vastly to bacterial evolution, allowing specialized traits to 'jump ship' between one lineage or species and the next. The benefits of this generosity from the point of view of both recipient cell and plasmid are generally understood: plasmids receive new hosts and ride out selective sweeps across the population, recipient cells gain new traits (such as antibiotic resistance). Explaining this behavior from the point of view of donor cells is substantially more difficult. Donor cells pay a fitness cost in order to share plasmids, and run the risk of sharing advantageous genes with their competition and rendering their own lineage redundant, while seemingly receiving no benefit in return. Using both compartment based models and agent based simulations we demonstrate that 'secretive' genes which restrict horizontal gene transfer are favored over a wide range of models and parameter values, even when sharing carries no direct cost. 'Generous' chromosomal genes which are more permissive of plasmid transfer are found to have neutral fitness at best, and are generally disfavored by selection. Our findings lead to a peculiar paradox: given the obvious benefits of keeping secrets, why do bacteria share information so freely?
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Affiliation(s)
- Alastair D Jamieson-Lane
- Department of Mathematics, University of Auckland, Auckland, 1010, New Zealand
- Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky, Universität Oldenburg, Oldenburg, 26129, Germany. Helmholtz Institute for Functional Marine Biodiversity, Carl von Ossietzky, Universität Oldenburg, Oldenburg, 26129, Germany
| | - Bernd Blasius
- Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky, Universität Oldenburg, Oldenburg, 26129, Germany. Helmholtz Institute for Functional Marine Biodiversity, Carl von Ossietzky, Universität Oldenburg, Oldenburg, 26129, Germany
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10
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Domingues CPF, Rebelo JS, Monteiro F, Nogueira T, Dionisio F. Harmful behaviour through plasmid transfer: a successful evolutionary strategy of bacteria harbouring conjugative plasmids. Philos Trans R Soc Lond B Biol Sci 2022; 377:20200473. [PMID: 34839709 PMCID: PMC8628071 DOI: 10.1098/rstb.2020.0473] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Conjugative plasmids are extrachromosomal mobile genetic elements pervasive among bacteria. Plasmids' acquisition often lowers cells' growth rate, so their ubiquity has been a matter of debate. Chromosomes occasionally mutate, rendering plasmids cost-free. However, these compensatory mutations typically take hundreds of generations to appear after plasmid arrival. By then, it could be too late to compete with fast-growing plasmid-free cells successfully. Moreover, arriving plasmids would have to wait hundreds of generations for compensatory mutations to appear in the chromosome of their new host. We hypothesize that plasmid-donor cells may use the plasmid as a 'weapon' to compete with plasmid-free cells, particularly in structured environments. Cells already adapted to plasmids may increase their inclusive fitness through plasmid transfer to impose a cost to nearby plasmid-free cells and increase the replication opportunities of nearby relatives. A mathematical model suggests conditions under which the proposed hypothesis works, and computer simulations tested the long-term plasmid maintenance. Our hypothesis explains the maintenance of conjugative plasmids not coding for beneficial genes. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.
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Affiliation(s)
- Célia P. F. Domingues
- Evolutionary Ecology of Microorganisms Group, cE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal,INIAV - Instituto Nacional de Investigação Agrária e Veterinária, I.P., Oeiras and Vairão, Portugal
| | - João S. Rebelo
- Evolutionary Ecology of Microorganisms Group, cE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
| | - Francisca Monteiro
- Evolutionary Ecology of Microorganisms Group, cE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
| | - Teresa Nogueira
- Evolutionary Ecology of Microorganisms Group, cE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal,INIAV - Instituto Nacional de Investigação Agrária e Veterinária, I.P., Oeiras and Vairão, Portugal
| | - Francisco Dionisio
- Evolutionary Ecology of Microorganisms Group, cE3c – Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal
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11
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Brockhurst MA, Harrison E. Ecological and evolutionary solutions to the plasmid paradox. Trends Microbiol 2021; 30:534-543. [PMID: 34848115 DOI: 10.1016/j.tim.2021.11.001] [Citation(s) in RCA: 46] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 10/07/2021] [Accepted: 11/03/2021] [Indexed: 12/22/2022]
Abstract
The 'plasmid paradox' arises because, although plasmids are common features of bacterial genomes, theoretically they should not exist: rates of conjugation were believed insufficient to allow plasmids to persist by infectious transmission, whereas the costs of plasmid maintenance meant that plasmids should be purged by negative selection regardless of whether they encoded beneficial accessory traits because these traits should eventually be captured by the chromosome, enabling the loss of the redundant plasmid. In the decade since the plasmid paradox was described, new data and theory show that a range of ecological and evolutionary mechanisms operate in bacterial populations and communities to explain the widespread distribution and stable maintenance of plasmids. We conclude, therefore, that multiple solutions to the plasmid paradox are now well understood. The current challenge for the field, however, is to better understand how these solutions operate in natural bacterial communities to explain and predict the distribution of plasmids and the dynamics of the horizontal gene transfer that they mediate in bacterial (pan)genomes.
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Affiliation(s)
- Michael A Brockhurst
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine, and Health, The University of Manchester, Manchester, M13 9PT, UK.
| | - Ellie Harrison
- Department of Animal and Plant Sciences, The University of Sheffield, Sheffield, S10 2TN, UK
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12
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Hernández-Beltrán JCR, San Millán A, Fuentes-Hernández A, Peña-Miller R. Mathematical Models of Plasmid Population Dynamics. Front Microbiol 2021; 12:606396. [PMID: 34803935 PMCID: PMC8600371 DOI: 10.3389/fmicb.2021.606396] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 10/14/2021] [Indexed: 11/24/2022] Open
Abstract
With plasmid-mediated antibiotic resistance thriving and threatening to become a serious public health problem, it is paramount to increase our understanding of the forces that enable the spread and maintenance of drug resistance genes encoded in mobile genetic elements. The relevance of plasmids as vehicles for the dissemination of antibiotic resistance genes, in addition to the extensive use of plasmid-derived vectors for biotechnological and industrial purposes, has promoted the in-depth study of the molecular mechanisms controlling multiple aspects of a plasmids' life cycle. This body of experimental work has been paralleled by the development of a wealth of mathematical models aimed at understanding the interplay between transmission, replication, and segregation, as well as their consequences in the ecological and evolutionary dynamics of plasmid-bearing bacterial populations. In this review, we discuss theoretical models of plasmid dynamics that span from the molecular mechanisms of plasmid partition and copy-number control occurring at a cellular level, to their consequences in the population dynamics of complex microbial communities. We conclude by discussing future directions for this exciting research topic.
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Affiliation(s)
| | | | | | - Rafael Peña-Miller
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
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13
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Pinilla-Redondo R, Russel J, Mayo-Muñoz D, Shah SA, Garrett RA, Nesme J, Madsen JS, Fineran PC, Sørensen SJ. CRISPR-Cas systems are widespread accessory elements across bacterial and archaeal plasmids. Nucleic Acids Res 2021; 50:4315-4328. [PMID: 34606604 PMCID: PMC9071438 DOI: 10.1093/nar/gkab859] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 09/08/2021] [Accepted: 10/02/2021] [Indexed: 12/12/2022] Open
Abstract
Many prokaryotes encode CRISPR-Cas systems as immune protection against mobile genetic elements (MGEs), yet a number of MGEs also harbor CRISPR-Cas components. With a few exceptions, CRISPR-Cas loci encoded on MGEs are uncharted and a comprehensive analysis of their distribution, prevalence, diversity, and function is lacking. Here, we systematically investigated CRISPR-Cas loci across the largest curated collection of natural bacterial and archaeal plasmids. CRISPR-Cas loci are widely but heterogeneously distributed across plasmids and, in comparison to host chromosomes, their mean prevalence per Mbp is higher and their distribution is distinct. Furthermore, the spacer content of plasmid CRISPRs exhibits a strong targeting bias towards other plasmids, while chromosomal arrays are enriched with virus-targeting spacers. These contrasting targeting preferences highlight the genetic independence of plasmids and suggest a major role for mediating plasmid-plasmid conflicts. Altogether, CRISPR-Cas are frequent accessory components of many plasmids, which is an overlooked phenomenon that possibly facilitates their dissemination across microbiomes.
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Affiliation(s)
- Rafael Pinilla-Redondo
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark.,Department of Technological Educations, University College Copenhagen, Sigurdsgade 26, 2200 Copenhagen, Denmark
| | - Jakob Russel
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
| | - David Mayo-Muñoz
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark.,Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Shiraz A Shah
- Copenhagen Prospective Studies on Asthma in Childhood (COPSAC), Herlev and Gentofte Hospital, University of Copenhagen, Ledreborg Alle 34, 2820 Gentofte, Denmark
| | - Roger A Garrett
- Danish Archaea Centre, Department of Biology, University of Copenhagen, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen, Denmark
| | - Joseph Nesme
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
| | - Jonas S Madsen
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
| | - Peter C Fineran
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand.,Bio-Protection Research Centre, University of Otago, Dunedin, New Zealand
| | - Søren J Sørensen
- Section of Microbiology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
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14
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Modeling the ecology of parasitic plasmids. THE ISME JOURNAL 2021; 15:2843-2852. [PMID: 33833414 PMCID: PMC8443676 DOI: 10.1038/s41396-021-00954-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 02/18/2021] [Accepted: 02/26/2021] [Indexed: 02/01/2023]
Abstract
Plasmids are autonomous genetic elements that can be exchanged between microorganisms via horizontal gene transfer (HGT). Despite the central role they play in antibiotic resistance and modern biotechnology, our understanding of plasmids' natural ecology is limited. Recent experiments have shown that plasmids can spread even when they are a burden to the cell, suggesting that natural plasmids may exist as parasites. Here, we use mathematical modeling to explore the ecology of such parasitic plasmids. We first develop models of single plasmids and find that a plasmid's population dynamics and optimal infection strategy are strongly determined by the plasmid's HGT mechanism. We then analyze models of co-infecting plasmids and show that parasitic plasmids are prone to a "tragedy of the commons" in which runaway plasmid invasion severely reduces host fitness. We propose that this tragedy of the commons is averted by selection between competing populations and demonstrate this effect in a metapopulation model. We derive predicted distributions of unique plasmid types in genomes-comparison to the distribution of plasmids in a collection of 17,725 genomes supports a model of parasitic plasmids with positive plasmid-plasmid interactions that ameliorate plasmid fitness costs or promote the invasion of new plasmids.
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15
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Lehtinen S, Huisman JS, Bonhoeffer S. Evolutionary mechanisms that determine which bacterial genes are carried on plasmids. Evol Lett 2021; 5:290-301. [PMID: 34136276 PMCID: PMC8190454 DOI: 10.1002/evl3.226] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 04/29/2021] [Indexed: 01/05/2023] Open
Abstract
The evolutionary pressures that determine the location (chromosomal or plasmid‐borne) of bacterial genes are not fully understood. We investigate these pressures through mathematical modeling in the context of antibiotic resistance, which is often found on plasmids. Our central finding is that gene location is under positive frequency‐dependent selection: the higher the frequency of one form of resistance compared to the other, the higher its relative fitness. This can keep moderately beneficial genes on plasmids, despite occasional plasmid loss. For these genes, positive frequency dependence leads to a priority effect: whichever form is acquired first—through either mutation or horizontal gene transfer—has time to increase in frequency and thus becomes difficult to displace. Higher rates of horizontal transfer of plasmid‐borne than chromosomal genes therefore predict moderately beneficial genes will be found on plasmids. Gene flow between plasmid and chromosome allows chromosomal forms to arise, but positive frequency‐dependent selection prevents these from establishing. Further modeling shows that this effect is particularly pronounced when genes are shared across a large number of species, suggesting that antibiotic resistance genes are often found on plasmids because they are moderately beneficial across many species. We also revisit previous theoretical work—relating to the role of local adaptation in explaining gene location and to plasmid persistence—in light of our findings.
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Affiliation(s)
- Sonja Lehtinen
- Department of Environmental System Science Institute for Integrative Biology, ETH Zürich Universitätstrasse 16 Zürich 8006 Switzerland
| | - Jana S Huisman
- Department of Environmental System Science Institute for Integrative Biology, ETH Zürich Universitätstrasse 16 Zürich 8006 Switzerland.,Swiss Institute of Bioinformatics Quartier Sorge Lausanne 1015 Switzerland
| | - Sebastian Bonhoeffer
- Department of Environmental System Science Institute for Integrative Biology, ETH Zürich Universitätstrasse 16 Zürich 8006 Switzerland
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16
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Alonso-Del Valle A, León-Sampedro R, Rodríguez-Beltrán J, DelaFuente J, Hernández-García M, Ruiz-Garbajosa P, Cantón R, Peña-Miller R, San Millán A. Variability of plasmid fitness effects contributes to plasmid persistence in bacterial communities. Nat Commun 2021; 12:2653. [PMID: 33976161 PMCID: PMC8113577 DOI: 10.1038/s41467-021-22849-y] [Citation(s) in RCA: 74] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 03/25/2021] [Indexed: 02/03/2023] Open
Abstract
Plasmid persistence in bacterial populations is strongly influenced by the fitness effects associated with plasmid carriage. However, plasmid fitness effects in wild-type bacterial hosts remain largely unexplored. In this study, we determined the fitness effects of the major antibiotic resistance plasmid pOXA-48_K8 in wild-type, ecologically compatible enterobacterial isolates from the human gut microbiota. Our results show that although pOXA-48_K8 produced an overall reduction in bacterial fitness, it produced small effects in most bacterial hosts, and even beneficial effects in several isolates. Moreover, genomic results showed a link between pOXA-48_K8 fitness effects and bacterial phylogeny, helping to explain plasmid epidemiology. Incorporating our fitness results into a simple population dynamics model revealed a new set of conditions for plasmid stability in bacterial communities, with plasmid persistence increasing with bacterial diversity and becoming less dependent on conjugation. These results help to explain the high prevalence of plasmids in the greatly diverse natural microbial communities.
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Affiliation(s)
- Aida Alonso-Del Valle
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
| | - Ricardo León-Sampedro
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
- Centro de Investigación Biológica en Red. Epidemiología y Salud Pública, Instituto de Salud Carlos III, Madrid, Spain
| | - Jerónimo Rodríguez-Beltrán
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
- Centro de Investigación Biológica en Red. Epidemiología y Salud Pública, Instituto de Salud Carlos III, Madrid, Spain
| | - Javier DelaFuente
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
| | - Marta Hernández-García
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
- Red Española de Investigación en Patología Infecciosa. Instituto de Salud Carlos III, Madrid, Spain
| | - Patricia Ruiz-Garbajosa
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
- Red Española de Investigación en Patología Infecciosa. Instituto de Salud Carlos III, Madrid, Spain
| | - Rafael Cantón
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain
- Red Española de Investigación en Patología Infecciosa. Instituto de Salud Carlos III, Madrid, Spain
| | - Rafael Peña-Miller
- Center for Genomic Sciences, Universidad Nacional Autónoma de México, Cuernavaca, Mexico.
| | - Alvaro San Millán
- Servicio de Microbiología. Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigación Sanitaria, Madrid, Spain.
- Centro de Investigación Biológica en Red. Epidemiología y Salud Pública, Instituto de Salud Carlos III, Madrid, Spain.
- Centro Nacional de Biotecnología-CSIC, Madrid, Spain.
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17
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Within-host bacterial growth dynamics with both mutation and horizontal gene transfer. J Math Biol 2021; 82:16. [PMID: 33544239 DOI: 10.1007/s00285-021-01571-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2019] [Revised: 01/08/2021] [Accepted: 01/19/2021] [Indexed: 10/22/2022]
Abstract
The evolution and emergence of antibiotic resistance is a major public health concern. The understanding of the within-host microbial dynamics combining mutational processes, horizontal gene transfer and resource consumption, is one of the keys to solving this problem. We analyze a generic model to rigorously describe interactions dynamics of four bacterial strains: one fully sensitive to the drug, one with mutational resistance only, one with plasmidic resistance only, and one with both resistances. By defining thresholds numbers (i.e. each strain's effective reproduction and each strain's transition threshold numbers), we first express conditions for the existence of non-trivial stationary states. We find that these thresholds mainly depend on bacteria quantitative traits such as nutrient consumption ability, growth conversion factor, death rate, mutation (forward or reverse), and segregational loss of plasmid probabilities (for plasmid-bearing strains). Next, concerning the order in the set of strain's effective reproduction thresholds numbers, we show that the qualitative dynamics of the model range from the extinction of all strains, coexistence of sensitive and mutational resistance strains, to the coexistence of all strains at equilibrium. Finally, we go through some applications of our general analysis depending on whether bacteria strains interact without or with drug action (either cytostatic or cytotoxic).
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18
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Zarei-Baygi A, Smith AL. Intracellular versus extracellular antibiotic resistance genes in the environment: Prevalence, horizontal transfer, and mitigation strategies. BIORESOURCE TECHNOLOGY 2021; 319:124181. [PMID: 33254446 DOI: 10.1016/j.biortech.2020.124181] [Citation(s) in RCA: 81] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 09/22/2020] [Accepted: 09/23/2020] [Indexed: 06/12/2023]
Abstract
Antibiotic resistance genes (ARGs) are present as both intracellular and extracellular fractions of DNA in the environment. Due to the poor yield of extracellular DNA in conventional extraction methods, previous studies have mainly focused on intracellular ARGs (iARGs). In this review, we evaluate the prevalence/persistence and horizontal transfer of iARGs and extracellular ARGs (eARGs) in different environments, and then explore advanced mitigation strategies in wastewater treatment plants (WWTPs) for preventing the spread of antibiotic resistance in the environment. Although iARGs are the main fraction of ARGs in nutrient-rich environments, eARGs are predominant in receiving aquatic environments. In such environments, natural transformation of eARGs occurs with a comparable frequency to conjugation of iARGs. Further, eARGs can be adsorbed by soil and sediments particles, protected from DNase degradation, and consequently persist longer than iARGs. Collectively, these characteristics emphasize the crucial role of eARGs in the spread of antibiotic resistance in the environment. Fate of iARGs and eARGs through advanced treatment technologies (disinfection and membrane filtration) indicates that different mitigation strategies may be required for each ARG fraction to be significantly removed. Finally, comprehensive risk assessment is needed to evaluate/compare the effect of iARGs versus eARGs in the environment.
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Affiliation(s)
- Ali Zarei-Baygi
- Astani Department of Civil and Environmental Engineering, University of Southern California, 920 Downey Way, Los Angeles, CA 90089, United States
| | - Adam L Smith
- Astani Department of Civil and Environmental Engineering, University of Southern California, 920 Downey Way, Los Angeles, CA 90089, United States.
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19
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Zwanzig M. The ecology of plasmid-coded antibiotic resistance: a basic framework for experimental research and modeling. Comput Struct Biotechnol J 2020; 19:586-599. [PMID: 33510864 PMCID: PMC7807137 DOI: 10.1016/j.csbj.2020.12.027] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 12/16/2020] [Accepted: 12/20/2020] [Indexed: 12/27/2022] Open
Abstract
Many antibiotic resistance genes are associated with plasmids. The ecological success of these mobile genetic elements within microbial communities depends on varying mechanisms to secure their own propagation, not only on environmental selection. Among the most important are the cost of plasmids and their ability to be transferred to new hosts through mechanisms such as conjugation. These are regulated by dynamic control systems of the conjugation machinery and genetic adaptations that plasmid-host pairs can acquire in coevolution. However, in complex communities, these processes and mechanisms are subject to a variety of interactions with other bacterial species and other plasmid types. This article summarizes basic plasmid properties and ecological principles particularly important for understanding the persistence of plasmid-coded antibiotic resistance in aquatic environments. Through selected examples, it further introduces to the features of different types of simulation models such as systems of ordinary differential equations and individual-based models, which are considered to be important tools to understand these complex systems. This ecological perspective aims to improve the way we study and understand the dynamics, diversity and persistence of plasmids and associated antibiotic resistance genes.
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Affiliation(s)
- Martin Zwanzig
- Faculty of Environmental Sciences, Technische Universität Dresden, Pienner Str. 8, D-01737 Tharandt, Germany
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20
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Gothwal R, Thatikonda S. Modeling transport of antibiotic resistant bacteria in aquatic environment using stochastic differential equations. Sci Rep 2020; 10:15081. [PMID: 32934268 PMCID: PMC7494867 DOI: 10.1038/s41598-020-72106-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Accepted: 08/24/2020] [Indexed: 11/09/2022] Open
Abstract
Contaminated sites are recognized as the "hotspot" for the development and spread of antibiotic resistance in environmental bacteria. It is very challenging to understand mechanism of development of antibiotic resistance in polluted environment in the presence of different anthropogenic pollutants. Uncertainties in the environmental processes adds complexity to the development of resistance. This study attempts to develop mathematical model by using stochastic partial differential equations for the transport of fluoroquinolone and its resistant bacteria in riverine environment. Poisson's process is assumed for the diffusion approximation in the stochastic partial differential equations (SPDE). Sensitive analysis is performed to evaluate the parameters and variables for their influence over the model outcome. Based on their sensitivity, the model parameters and variables are chosen and classified into environmental, demographic, and anthropogenic categories to investigate the sources of stochasticity. Stochastic partial differential equations are formulated for the state variables in the model. This SPDE model is then applied to the 100 km stretch of river Musi (South India) and simulations are carried out to assess the impact of stochasticity in model variables on the resistant bacteria population in sediments. By employing the stochasticity in model variables and parameters we came to know that environmental and anthropogenic variations are not able to affect the resistance dynamics at all. Demographic variations are able to affect the distribution of resistant bacteria population uniformly with standard deviation between 0.087 and 0.084, however, is not significant to have any biological relevance to it. The outcome of the present study is helpful in simplifying the model for practical applications. This study is an ongoing effort to improve the model for the transport of antibiotics and transport of antibiotic resistant bacteria in polluted river. There is a wide gap between the knowledge of stochastic resistant bacterial growth dynamics and the knowledge of transport of antibiotic resistance in polluted aquatic environment, this study is one step towards filling up that gap.
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Affiliation(s)
- Ritu Gothwal
- Department of Civil Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy, Telangana, 502285, India
| | - Shashidhar Thatikonda
- Department of Civil Engineering, Indian Institute of Technology Hyderabad, Kandi, Sangareddy, Telangana, 502285, India.
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21
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Tepekule B, Abel Zur Wiesch P, Kouyos RD, Bonhoeffer S. Quantifying the impact of treatment history on plasmid-mediated resistance evolution in human gut microbiota. Proc Natl Acad Sci U S A 2019; 116:23106-23116. [PMID: 31666328 PMCID: PMC6859334 DOI: 10.1073/pnas.1912188116] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
To understand how antibiotic use affects the risk of a resistant infection, we present a computational model of the population dynamics of gut microbiota including antibiotic resistance-conferring plasmids. We then describe how this model is parameterized based on published microbiota data. Finally, we investigate how treatment history affects the prevalence of resistance among opportunistic enterobacterial pathogens. We simulate treatment histories and identify which properties of prior antibiotic exposure are most influential in determining the prevalence of resistance. We find that resistance prevalence can be predicted by 3 properties, namely the total days of drug exposure, the duration of the drug-free period after last treatment, and the center of mass of the treatment pattern. Overall this work provides a framework for capturing the role of the microbiome in the selection of antibiotic resistance and highlights the role of treatment history for the prevalence of resistance.
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Affiliation(s)
- Burcu Tepekule
- Department of Environmental Systems Science, Eidgenössische Technische Hochschule Zurich, 8092 Zurich, Switzerland;
| | - Pia Abel Zur Wiesch
- Department of Pharmacy, Faculty of Health Sciences, UiT-The Arctic University of Norway, 9037 Tromsø, Norway
- Centre for Molecular Medicine Norway, 0318 Oslo, Norway
| | - Roger D Kouyos
- Department of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, 8091 Zurich, Switzerland
- Institute of Medical Virology, University of Zurich, 8057 Zurich, Switzerland
| | - Sebastian Bonhoeffer
- Department of Environmental Systems Science, Eidgenössische Technische Hochschule Zurich, 8092 Zurich, Switzerland
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22
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Antimicrobial Resistance in Bacteria: Mechanisms, Evolution, and Persistence. J Mol Evol 2019; 88:26-40. [PMID: 31659373 DOI: 10.1007/s00239-019-09914-3] [Citation(s) in RCA: 254] [Impact Index Per Article: 50.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Accepted: 10/02/2019] [Indexed: 01/29/2023]
Abstract
In recent years, we have seen antimicrobial resistance rapidly emerge at a global scale and spread from one country to the other faster than previously thought. Superbugs and multidrug-resistant bacteria are endemic in many parts of the world. There is no question that the widespread use, overuse, and misuse of antimicrobials during the last 80 years have been associated with the explosion of antimicrobial resistance. On the other hand, the molecular pathways behind the emergence of antimicrobial resistance in bacteria were present since ancient times. Some of these mechanisms are the ancestors of current resistance determinants. Evidently, there are plenty of putative resistance genes in the environment, however, we cannot yet predict which ones would be able to be expressed as phenotypes in pathogenic bacteria and cause clinical disease. In addition, in the presence of inhibitory and sub-inhibitory concentrations of antibiotics in natural habitats, one could assume that novel resistance mechanisms will arise against antimicrobial compounds. This review presents an overview of antimicrobial resistance mechanisms, and describes how these have evolved and how they continue to emerge. As antimicrobial strategies able to bypass the development of resistance are urgently needed, a better understanding of the critical factors that contribute to the persistence and spread of antimicrobial resistance may yield innovative perspectives on the design of such new therapeutic targets.
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23
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Emergence of plasmid stability under non-selective conditions maintains antibiotic resistance. Nat Commun 2019; 10:2595. [PMID: 31197163 PMCID: PMC6565834 DOI: 10.1038/s41467-019-10600-7] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2019] [Accepted: 05/21/2019] [Indexed: 01/21/2023] Open
Abstract
Plasmid acquisition is an important mechanism of rapid adaptation and niche expansion in prokaryotes. Positive selection for plasmid-coded functions is a major driver of plasmid evolution, while plasmids that do not confer a selective advantage are considered costly and expected to go extinct. Yet, plasmids are ubiquitous in nature, and their persistence remains an evolutionary paradox. Here, we demonstrate that non-mobile plasmids persist over evolutionary timescales without selection for the plasmid function. Evolving a minimal plasmid encoding for antibiotics resistance in Escherichia coli, we discover that plasmid stability emerges in the absence of antibiotics and that plasmid loss is determined by transcription-replication conflicts. We further find that environmental conditions modulate these conflicts and plasmid persistence. Silencing the transcription of the resistance gene results in stable plasmids that become fixed in the population. Evolution of plasmid stability under non-selective conditions provides an evolutionary explanation for the ubiquity of plasmids in nature. It is expected that plasmids are costly and therefore that selection is required to maintain them within bacterial populations. Here, Wein et al. show that plasmid stability can emerge even in the absence of positive selection and that loss may be determined by transcription-replication conflict.
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24
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Stevenson C, Hall JPJ, Brockhurst MA, Harrison E. Plasmid stability is enhanced by higher-frequency pulses of positive selection. Proc Biol Sci 2019; 285:rspb.2017.2497. [PMID: 29321301 PMCID: PMC5784203 DOI: 10.1098/rspb.2017.2497] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 12/01/2017] [Indexed: 11/22/2022] Open
Abstract
Plasmids accelerate bacterial adaptation by sharing ecologically important traits between lineages. However, explaining plasmid stability in bacterial populations is challenging owing to their associated costs. Previous theoretical and experimental studies suggest that pulsed positive selection may explain plasmid stability by favouring gene mobility and promoting compensatory evolution to ameliorate plasmid cost. Here we test how the frequency of pulsed positive selection affected the dynamics of a mercury-resistance plasmid, pQBR103, in experimental populations of Pseudomonas fluorescens SBW25. Plasmid dynamics varied according to the frequency of Hg2+ positive selection: in the absence of Hg2+ plasmids declined to low frequency, whereas pulses of Hg2+ selection allowed plasmids to sweep to high prevalence. Compensatory evolution to ameliorate the cost of plasmid carriage was widespread across the entire range of Hg2+ selection regimes, including both constant and pulsed Hg2+ selection. Consistent with theoretical predictions, gene mobility via conjugation appeared to play a greater role in promoting plasmid stability under low-frequency pulses of Hg2+ selection. However, upon removal of Hg2+ selection, plasmids which had evolved under low-frequency pulse selective regimes declined over time. Our findings suggest that temporally variable selection environments, such as those created during antibiotic treatments, may help to explain the stability of mobile plasmid-encoded resistance.
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Affiliation(s)
- Cagla Stevenson
- Department of Biology, University of York, York YO10 5DD, UK .,Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
| | - James P J Hall
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
| | - Michael A Brockhurst
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
| | - Ellie Harrison
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
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25
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Mobile Compensatory Mutations Promote Plasmid Survival. mSystems 2019; 4:mSystems00186-18. [PMID: 30944871 PMCID: PMC6446977 DOI: 10.1128/msystems.00186-18] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 12/13/2018] [Indexed: 01/15/2023] Open
Abstract
The global dissemination of plasmids encoding antibiotic resistance represents an urgent issue for human health and society. While the fitness costs for host cells associated with plasmid acquisition are expected to limit plasmid dissemination in the absence of positive selection of plasmid traits, compensatory evolution can reduce this burden. Experimental data suggest that compensatory mutations can be located on either the chromosome or the plasmid, and these are likely to have contrasting effects on plasmid dynamics. Whereas chromosomal mutations are inherited vertically through bacterial fission, plasmid mutations can be inherited both vertically and horizontally and potentially reduce the initial cost of the plasmid in new host cells. Here we show using mathematical models and simulations that the dynamics of plasmids depends critically on the genomic location of the compensatory mutation. We demonstrate that plasmid-located compensatory evolution is better at enhancing plasmid persistence, even when its effects are smaller than those provided by chromosomal compensation. Moreover, either type of compensatory evolution facilitates the survival of resistance plasmids at low drug concentrations. These insights contribute to an improved understanding of the conditions and mechanisms driving the spread and the evolution of antibiotic resistance plasmids. IMPORTANCE Understanding the evolutionary forces that maintain antibiotic resistance genes in a population, especially when antibiotics are not used, is an important problem for human health and society. The most common platform for the dissemination of antibiotic resistance genes is conjugative plasmids. Experimental studies showed that mutations located on the plasmid or the bacterial chromosome can reduce the costs plasmids impose on their hosts, resulting in antibiotic resistance plasmids being maintained even in the absence of antibiotics. While chromosomal mutations are only vertically inherited by the daughter cells, plasmid mutations are also provided to bacteria that acquire the plasmid through conjugation. Here we demonstrate how the mode of inheritance of a compensatory mutation crucially influences the ability of plasmids to spread and persist in a bacterial population.
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26
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Black Queen Evolution and Trophic Interactions Determine Plasmid Survival after the Disruption of the Conjugation Network. mSystems 2018; 3:mSystems00104-18. [PMID: 30320219 PMCID: PMC6172774 DOI: 10.1128/msystems.00104-18] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 08/30/2018] [Indexed: 01/21/2023] Open
Abstract
Bacterial antibiotic resistance is often a part of mobile genetic elements that move from one bacterium to another. By interfering with the horizontal movement and the maintenance of these elements, it is possible to remove the resistance from the population. Here, we show that a so-called plasmid-dependent bacteriophage causes the initially resistant bacterial population to become susceptible to antibiotics. However, this effect is efficiently countered when the system also contains a predator that feeds on bacteria. Moreover, when the environment contains antibiotics, the survival of resistance is dependent on the resistance mechanism. When bacteria can help their contemporaries to degrade antibiotics, resistance is maintained by only a fraction of the community. On the other hand, when bacteria cannot help others, then all bacteria remain resistant. The concentration of the antibiotic played a less notable role than the antibiotic used. This report shows that the survival of antibiotic resistance in bacterial communities represents a complex process where many factors present in real-life systems define whether or not resistance is actually lost. Mobile genetic elements such as conjugative plasmids are responsible for antibiotic resistance phenotypes in many bacterial pathogens. The ability to conjugate, the presence of antibiotics, and ecological interactions all have a notable role in the persistence of plasmids in bacterial populations. Here, we set out to investigate the contribution of these factors when the conjugation network was disturbed by a plasmid-dependent bacteriophage. Phage alone effectively caused the population to lose plasmids, thus rendering them susceptible to antibiotics. Leakiness of the antibiotic resistance mechanism allowing Black Queen evolution (i.e. a “race to the bottom”) was a more significant factor than the antibiotic concentration (lethal vs sublethal) in determining plasmid prevalence. Interestingly, plasmid loss was also prevented by protozoan predation. These results show that outcomes of attempts to resensitize bacterial communities by disrupting the conjugation network are highly dependent on ecological factors and resistance mechanisms. IMPORTANCE Bacterial antibiotic resistance is often a part of mobile genetic elements that move from one bacterium to another. By interfering with the horizontal movement and the maintenance of these elements, it is possible to remove the resistance from the population. Here, we show that a so-called plasmid-dependent bacteriophage causes the initially resistant bacterial population to become susceptible to antibiotics. However, this effect is efficiently countered when the system also contains a predator that feeds on bacteria. Moreover, when the environment contains antibiotics, the survival of resistance is dependent on the resistance mechanism. When bacteria can help their contemporaries to degrade antibiotics, resistance is maintained by only a fraction of the community. On the other hand, when bacteria cannot help others, then all bacteria remain resistant. The concentration of the antibiotic played a less notable role than the antibiotic used. This report shows that the survival of antibiotic resistance in bacterial communities represents a complex process where many factors present in real-life systems define whether or not resistance is actually lost.
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27
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Standley MS, Million-Weaver S, Alexander DL, Hu S, Camps M. Genetic control of ColE1 plasmid stability that is independent of plasmid copy number regulation. Curr Genet 2018; 65:179-192. [PMID: 29909438 DOI: 10.1007/s00294-018-0858-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 06/08/2018] [Accepted: 06/12/2018] [Indexed: 02/07/2023]
Abstract
ColE1-like plasmid vectors are widely used for expression of recombinant genes in E. coli. For these vectors, segregation of individual plasmids into daughter cells during cell division appears to be random, making them susceptible to loss over time when no mechanisms ensuring their maintenance are present. Here we use the plasmid pGFPuv in a recA relA strain as a sensitized model to study factors affecting plasmid stability in the context of recombinant gene expression. We find that in this model, plasmid stability can be restored by two types of genetic modifications to the plasmid origin of replication (ori) sequence: point mutations and a novel 269 nt duplication at the 5' end of the plasmid ori, which we named DAS (duplicated anti-sense) ori. Combinations of these modifications produce a range of copy numbers and of levels of recombinant expression. In direct contradiction with the classic random distribution model, we find no correlation between increased plasmid copy number and increased plasmid stability. Increased stability cannot be explained by reduced levels of recombinant gene expression either. Our observations would be more compatible with a hybrid clustered and free-distribution model, which has been recently proposed based on detection of individual plasmids in vivo using super-resolution fluorescence microscopy. This work suggests a role for the plasmid ori in the control of segregation of ColE1 plasmids that is distinct from replication initiation, opening the door for the genetic regulation of plasmid stability as a strategy aimed at enhancing large-scale recombinant gene expression or bioremediation.
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Affiliation(s)
- Melissa S Standley
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA, 95064, USA
| | - Samuel Million-Weaver
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA, 95064, USA
- College of Engineering, University of Wisconsin-Madison, Madison, 53706, USA
| | - David L Alexander
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA, 95064, USA
- Department of Biomolecular Engineering, UCSC, Santa Cruz, USA
| | - Shuai Hu
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA, 95064, USA
| | - Manel Camps
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA, 95064, USA.
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28
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Abstract
Plasmids mediate the horizontal transmission of genetic information between bacteria, facilitating their adaptation to multiple environmental conditions. An especially important example of the ability of plasmids to catalyze bacterial adaptation and evolution is their instrumental role in the global spread of antibiotic resistance, which constitutes a major threat to public health. Plasmids provide bacteria with new adaptive tools, but they also entail a metabolic burden that, in the absence of selection for plasmid-encoded traits, reduces the competitiveness of the plasmid-carrying clone. Although this fitness reduction can be alleviated over time through compensatory evolution, the initial cost associated with plasmid carriage is the main constraint on the vertical and horizontal replication of these genetic elements. The fitness effects of plasmids therefore have a crucial influence on their ability to associate with new bacterial hosts and consequently on the evolution of plasmid-mediated antibiotic resistance. However, the molecular mechanisms underlying plasmid fitness cost remain poorly understood. Here, we analyze the literature in the field and examine the potential fitness effects produced by plasmids throughout their life cycle in the host bacterium. We also explore the various mechanisms evolved by plasmids and bacteria to minimize the cost entailed by these mobile genetic elements. Finally, we discuss potential future research directions in the field.
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Abstract
Plasmids are extrachromosomal DNA elements that can be found throughout bacteria, as well as in other domains of life. Nonetheless, the evolutionary processes underlying the persistence of plasmids are incompletely understood. Bacterial plasmids may encode genes for traits that are sometimes beneficial to their hosts, such as antimicrobial resistance, virulence, heavy metal tolerance, and the catabolism of unique nutrient sources. In the absence of selection for these traits, however, plasmids generally impose a fitness cost on their hosts. As such, plasmid persistence presents a conundrum: models predict that costly plasmids will be lost over time or that beneficial plasmid genes will be integrated into the host genome. However, laboratory and comparative studies have shown that plasmids can persist for long periods, even in the absence of positive selection. Several hypotheses have been proposed to explain plasmid persistence, including host-plasmid co-adaptation, plasmid hitchhiking, cross-ecotype transfer, and high plasmid transfer rates, but there is no clear evidence that any one model adequately resolves the plasmid paradox.
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Affiliation(s)
- Amanda C Carroll
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.,Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada
| | - Alex Wong
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.,Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada
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Zhang M, Chen L, Ye C, Yu X. Co-selection of antibiotic resistance via copper shock loading on bacteria from a drinking water bio-filter. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2018; 233:132-141. [PMID: 29059628 DOI: 10.1016/j.envpol.2017.09.084] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 09/13/2017] [Accepted: 09/26/2017] [Indexed: 06/07/2023]
Abstract
Heavy metal contamination of source water frequently occurred in developing countries as a result of accidents. To address the problems, most of the previous studies have focused on engineering countermeasures. In this study, we investigated the effects of heavy metals, particularly copper, on the development of antibiotic resistance by establishing a copper shock loading test. Results revealed that co-selection occurred rapidly within 6 h. Copper, at the levels of 10 and 100 mg/L, significantly increased bacterial resistance to the antibiotics tested, including rifampin, erythromycin, kanamycin, and a few others. A total of 117 antimicrobial-resistance genes were detected from 12 types of genes, and the relative abundance of most genes (particularly mobile genetic elements intⅠand transposons) was markedly enriched by at least one fold. Furthermore, the copper shock loading altered the bacterial community. Numerous heavy metal and antibiotic resistant strains were screened out and enriched. These strains are expected to enhance the overall level of resistance. More noticeably, the majority of the co-selected antibiotic resistance could sustain for at least 20 h in the absence of copper and antimicrobial drugs. Resistance to vancomycin, erythromycin and lincomycin even could remain for 7 days. The prominent selection pressure by the copper shock loading implies that a real accident most likely poses similar impacts on the water environment. An accidental release of heavy metals would not only cause harm to the ecological environment, but also contribute to the development of bacterial antibiotic resistance. Broader concerns should be raised about the biological risks caused by sudden releases of pollutants by accidents.
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Affiliation(s)
- Menglu Zhang
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, People's Republic of China; University of Chinese Academy of Science, Beijing 100049, People's Republic of China
| | - Lihua Chen
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, People's Republic of China; University of Chinese Academy of Science, Beijing 100049, People's Republic of China
| | - Chengsong Ye
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, People's Republic of China
| | - Xin Yu
- Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, People's Republic of China.
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31
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Lopatkin AJ, Meredith HR, Srimani JK, Pfeiffer C, Durrett R, You L. Persistence and reversal of plasmid-mediated antibiotic resistance. Nat Commun 2017; 8:1689. [PMID: 29162798 PMCID: PMC5698434 DOI: 10.1038/s41467-017-01532-1] [Citation(s) in RCA: 187] [Impact Index Per Article: 26.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 09/22/2017] [Indexed: 02/07/2023] Open
Abstract
In the absence of antibiotic-mediated selection, sensitive bacteria are expected to displace their resistant counterparts if resistance genes are costly. However, many resistance genes persist for long periods in the absence of antibiotics. Horizontal gene transfer (primarily conjugation) could explain this persistence, but it has been suggested that very high conjugation rates would be required. Here, we show that common conjugal plasmids, even when costly, are indeed transferred at sufficiently high rates to be maintained in the absence of antibiotics in Escherichia coli. The notion is applicable to nine plasmids from six major incompatibility groups and mixed populations carrying multiple plasmids. These results suggest that reducing antibiotic use alone is likely insufficient for reversing resistance. Therefore, combining conjugation inhibition and promoting plasmid loss would be an effective strategy to limit conjugation-assisted persistence of antibiotic resistance. It is unclear whether the transfer of plasmids carrying antibiotic resistance genes can explain their persistence when antibiotics are not present. Here, Lopatkin et al. show that conjugal plasmids, even when costly, are indeed transferred at sufficiently high rates to be maintained in the absence of antibiotics.
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Affiliation(s)
- Allison J Lopatkin
- Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA
| | - Hannah R Meredith
- Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA
| | - Jaydeep K Srimani
- Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA
| | - Connor Pfeiffer
- Department of Biology, Duke University, Durham, NC, 27708, USA
| | - Rick Durrett
- Department of Mathematics, Duke University, Durham, NC, 27708, USA
| | - Lingchong You
- Department of Biomedical Engineering, Duke University, Durham, NC, 27708, USA. .,Center for Genomic and Computational Biology, Duke University, Durham, NC, 27708, USA. .,Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC, 27710, USA.
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32
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Botts RT, Apffel BA, Walters CJ, Davidson KE, Echols RS, Geiger MR, Guzman VL, Haase VS, Montana MA, La Chat CA, Mielke JA, Mullen KL, Virtue CC, Brown CJ, Top EM, Cummings DE. Characterization of Four Multidrug Resistance Plasmids Captured from the Sediments of an Urban Coastal Wetland. Front Microbiol 2017; 8:1922. [PMID: 29067005 PMCID: PMC5641379 DOI: 10.3389/fmicb.2017.01922] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Accepted: 09/21/2017] [Indexed: 11/17/2022] Open
Abstract
Self-transmissible and mobilizable plasmids contribute to the emergence and spread of multidrug-resistant bacteria by enabling the horizontal transfer of acquired antibiotic resistance. The objective of this study was to capture and characterize self-transmissible and mobilizable resistance plasmids from a coastal wetland impacted by urban stormwater runoff and human wastewater during the rainy season. Four plasmids were captured, two self-transmissible and two mobilizable, using both mating and enrichment approaches. Plasmid genomes, sequenced with either Illumina or PacBio platforms, revealed representatives of incompatibility groups IncP-6, IncR, IncN3, and IncF. The plasmids ranged in size from 36 to 144 kb and encoded known resistance genes for most of the major classes of antibiotics used to treat Gram-negative infections (tetracyclines, sulfonamides, β-lactams, fluoroquinolones, aminoglycosides, and amphenicols). The mobilizable IncP-6 plasmid pLNU-11 was discovered in a strain of Citrobacter freundii enriched from the wetland sediments with tetracycline and nalidixic acid, and encodes a novel AmpC-like β-lactamase (blaWDC-1), which shares less than 62% amino acid sequence identity with the PDC class of β-lactamases found in Pseudomonas aeruginosa. Although the IncR plasmid pTRE-1611 was captured by mating wetland bacteria with P. putida KT2440 as recipient, it was found to be mobilizable rather than self-transmissible. Two self-transmissible multidrug-resistance plasmids were also captured: the small (48 kb) IncN3 plasmid pTRE-131 was captured by mating wetland bacteria with Escherichia coli HY842 where it is seemed to be maintained at nearly 240 copies per cell, while the large (144 kb) IncF plasmid pTRE-2011, which was isolated from a cefotaxime-resistant environmental strain of E. coli ST744, exists at just a single copy per cell. Furthermore, pTRE-2011 bears the globally epidemic blaCTX-M-55 extended-spectrum β-lactamase downstream of ISEcp1. Our results indicate that urban coastal wetlands are reservoirs of diverse self-transmissible and mobilizable plasmids of relevance to human health.
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Affiliation(s)
- Ryan T Botts
- Department of Mathematical, Information and Computer Sciences, Point Loma Nazarene University, San Diego, CA, United States
| | - Brooke A Apffel
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - C J Walters
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Kelly E Davidson
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Ryan S Echols
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Michael R Geiger
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Victoria L Guzman
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Victoria S Haase
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Michal A Montana
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Chip A La Chat
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Jenna A Mielke
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Kelly L Mullen
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Cierra C Virtue
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
| | - Celeste J Brown
- Department of Biological Sciences, Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID, United States
| | - Eva M Top
- Department of Biological Sciences, Institute for Bioinformatics and Evolutionary Studies, University of Idaho, Moscow, ID, United States
| | - David E Cummings
- Department of Biology, Point Loma Nazarene University, San Diego, CA, United States
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Ramsay JP, Firth N. Diverse mobilization strategies facilitate transfer of non-conjugative mobile genetic elements. Curr Opin Microbiol 2017; 38:1-9. [PMID: 28391142 DOI: 10.1016/j.mib.2017.03.003] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 03/14/2017] [Indexed: 10/19/2022]
Abstract
Conjugation is a dominant mechanism of horizontal gene transfer and substantially contributes to the plasticity and evolvability of prokaryotic genomes. The impact of conjugation on genetic flux extends well beyond self-transmissible conjugative elements, because non-conjugative 'mobilizable elements' utilize other elements' conjugative apparatus for transfer. Bacterial genome comparisons highlight plasmids as vehicles for dissemination of pathogenesis and antimicrobial-resistance determinants, but for most non-conjugative plasmids, a mobilization mechanism is not apparent. Recently we discovered many Staphylococcus aureus plasmids lacking mobilization genes carry oriT sequences that mimic those on conjugative plasmids, suggesting that significantly more elements may be mobilizable than previously recognized. Here we summarize our findings, review the diverse mobilization strategies employed by mobile genetic elements and discuss implications for future gene-transfer research.
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Affiliation(s)
- Joshua P Ramsay
- School of Biomedical Sciences and Curtin Health Innovation Research Institute, Curtin University, Perth, Western Australia, Australia.
| | - Neville Firth
- School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia
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34
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The effect of competition and horizontal trait inheritance on invasion, fixation, and polymorphism. J Theor Biol 2016; 411:48-58. [DOI: 10.1016/j.jtbi.2016.10.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Revised: 09/19/2016] [Accepted: 10/06/2016] [Indexed: 11/19/2022]
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35
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Paterson IK, Hoyle A, Ochoa G, Baker-Austin C, Taylor NGH. Optimising Antibiotic Usage to Treat Bacterial Infections. Sci Rep 2016; 6:37853. [PMID: 27892497 PMCID: PMC5124968 DOI: 10.1038/srep37853] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Accepted: 11/02/2016] [Indexed: 12/23/2022] Open
Abstract
The increase in antibiotic resistant bacteria poses a threat to the continued use of antibiotics to treat bacterial infections. The overuse and misuse of antibiotics has been identified as a significant driver in the emergence of resistance. Finding optimal treatment regimens is therefore critical in ensuring the prolonged effectiveness of these antibiotics. This study uses mathematical modelling to analyse the effect traditional treatment regimens have on the dynamics of a bacterial infection. Using a novel approach, a genetic algorithm, the study then identifies improved treatment regimens. Using a single antibiotic the genetic algorithm identifies regimens which minimise the amount of antibiotic used while maximising bacterial eradication. Although exact treatments are highly dependent on parameter values and initial bacterial load, a significant common trend is identified throughout the results. A treatment regimen consisting of a high initial dose followed by an extended tapering of doses is found to optimise the use of antibiotics. This consistently improves the success of eradicating infections, uses less antibiotic than traditional regimens and reduces the time to eradication. The use of genetic algorithms to optimise treatment regimens enables an extensive search of possible regimens, with previous regimens directing the search into regions of better performance.
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Affiliation(s)
- Iona K Paterson
- University of Stirling, Computing Science and Mathematics, Faculty of Natural Sciences, Stirling, FK9 4LA, United Kingdom
| | - Andy Hoyle
- University of Stirling, Computing Science and Mathematics, Faculty of Natural Sciences, Stirling, FK9 4LA, United Kingdom
| | - Gabriela Ochoa
- University of Stirling, Computing Science and Mathematics, Faculty of Natural Sciences, Stirling, FK9 4LA, United Kingdom
| | - Craig Baker-Austin
- Centre for Environment, Fisheries and Aquaculture Science (Cefas), Weymouth Laboratory, Weymouth, DT4 8UB, United Kingdom
| | - Nick G H Taylor
- Centre for Environment, Fisheries and Aquaculture Science (Cefas), Weymouth Laboratory, Weymouth, DT4 8UB, United Kingdom
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36
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Medaney F, Ellis RJ, Raymond B. Ecological and genetic determinants of plasmid distribution inEscherichia coli. Environ Microbiol 2016; 18:4230-4239. [DOI: 10.1111/1462-2920.13552] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2016] [Revised: 08/19/2016] [Accepted: 09/26/2016] [Indexed: 01/07/2023]
Affiliation(s)
- Frances Medaney
- School of Biological Science; Royal Holloway University of London; Egham Surrey TW20 0EX UK
| | - Richard J. Ellis
- Specialist Scientific Support Department; Animal and Plant Health Agency, APHA Weybridge, Addlestone; Surrey KT15 3NB UK
| | - Ben Raymond
- School of Biological Science; Royal Holloway University of London; Egham Surrey TW20 0EX UK
- University of Exeter, Penryn Campus; Penryn Cornwall TR10 9FE UK
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37
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Mao J, Lu T. Population-Dynamic Modeling of Bacterial Horizontal Gene Transfer by Natural Transformation. Biophys J 2016; 110:258-68. [PMID: 26745428 PMCID: PMC4806214 DOI: 10.1016/j.bpj.2015.11.033] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 11/07/2015] [Accepted: 11/24/2015] [Indexed: 11/18/2022] Open
Abstract
Natural transformation is a major mechanism of horizontal gene transfer (HGT) and plays an essential role in bacterial adaptation, evolution, and speciation. Although its molecular underpinnings have been increasingly revealed, natural transformation is not well characterized in terms of its quantitative ecological roles. Here, by using Neisseria gonorrhoeae as an example, we developed a population-dynamic model for natural transformation and analyzed its dynamic characteristics with nonlinear tools and simulations. Our study showed that bacteria capable of natural transformation can display distinct population behaviors ranging from extinction to coexistence and to bistability, depending on their HGT rate and selection coefficient. With the model, we also illustrated the roles of environmental DNA sources-active secretion and passive release-in impacting population dynamics. Additionally, by constructing and utilizing a stochastic version of the model, we examined how noise shapes the steady and dynamic behaviors of the system. Notably, we found that distinct waiting time statistics for HGT events, namely a power-law distribution, an exponential distribution, and a mix of the both, are associated with the dynamics in the regimes of extinction, coexistence, and bistability accordingly. This work offers a quantitative illustration of natural transformation by revealing its complex population dynamics and associated characteristics, therefore advancing our ecological understanding of natural transformation as well as HGT in general.
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Affiliation(s)
- Junwen Mao
- Department of Physics, Huzhou University, Zhejiang, China; Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois
| | - Ting Lu
- Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Illinois; Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois; Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois.
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38
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Qiu Z, Shen Z, Qian D, Jin M, Yang D, Wang J, Zhang B, Yang Z, Chen Z, Wang X, Ding C, Wang D, Li JW. Effects of nano-TiO2on antibiotic resistance transfer mediated by RP4 plasmid. Nanotoxicology 2015; 9:895-904. [DOI: 10.3109/17435390.2014.991429] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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39
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O'Brien FG, Yui Eto K, Murphy RJT, Fairhurst HM, Coombs GW, Grubb WB, Ramsay JP. Origin-of-transfer sequences facilitate mobilisation of non-conjugative antimicrobial-resistance plasmids in Staphylococcus aureus. Nucleic Acids Res 2015; 43:7971-83. [PMID: 26243776 PMCID: PMC4652767 DOI: 10.1093/nar/gkv755] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Accepted: 07/14/2015] [Indexed: 11/17/2022] Open
Abstract
Staphylococcus aureus is a common cause of hospital, community and livestock-associated infections and is increasingly resistant to multiple antimicrobials. A significant proportion of antimicrobial-resistance genes are plasmid-borne, but only a minority of S. aureus plasmids encode proteins required for conjugative transfer or Mob relaxase proteins required for mobilisation. The pWBG749 family of S. aureus conjugative plasmids can facilitate the horizontal transfer of diverse antimicrobial-resistance plasmids that lack Mob genes. Here we reveal that these mobilisable plasmids carry copies of the pWBG749 origin-of-transfer (oriT) sequence and that these oriT sequences facilitate mobilisation by pWBG749. Sequences resembling the pWBG749 oriT were identified on half of all sequenced S. aureus plasmids, including the most prevalent large antimicrobial-resistance/virulence-gene plasmids, pIB485, pMW2 and pUSA300HOUMR. oriT sequences formed five subfamilies with distinct inverted-repeat-2 (IR2) sequences. pWBG749-family plasmids encoding each IR2 were identified and pWBG749 mobilisation was found to be specific for plasmids carrying matching IR2 sequences. Specificity of mobilisation was conferred by a putative ribbon-helix-helix-protein gene smpO. Several plasmids carried 2–3 oriT variants and pWBG749-mediated recombination occurred between distinct oriT sites during mobilisation. These observations suggest this relaxase-in trans mechanism of mobilisation by pWBG749-family plasmids is a common mechanism of plasmid dissemination in S. aureus.
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Affiliation(s)
- Frances G O'Brien
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia
| | - Karina Yui Eto
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia
| | - Riley J T Murphy
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia
| | - Heather M Fairhurst
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia
| | - Geoffrey W Coombs
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia PathWest Laboratory Medicine, Fiona Stanley Hospital, Perth, Western Australia, Australia
| | - Warren B Grubb
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia
| | - Joshua P Ramsay
- CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia
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40
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Abstract
Bacteriophages are a major cause of bacterial mortality and impose strong selection on natural bacterial populations, yet their effects on the dynamics of conjugative plasmids have rarely been tested. We combined experimental evolution, mathematical modeling, and individual-based simulations to explain how the ecological and population genetics effects of bacteriophages upon bacteria interact to determine the dynamics of conjugative plasmids and their persistence. The ecological effects of bacteriophages on bacteria are predicted to limit the existence conditions for conjugative plasmids, preventing persistence under weak selection for plasmid accessory traits. Experiments showed that phages drove faster extinction of plasmids in environments where the plasmid conferred no benefit, but they also revealed more complex effects of phages on plasmid dynamics under these conditions, specifically, the temporary maintenance of plasmids at fixation followed by rapid loss. We hypothesized that the population genetic effects of bacteriophages, specifically, selection for phage resistance mutations, may have caused this. Further mathematical modeling and individual-based simulations supported our hypothesis, showing that conjugative plasmids may hitchhike with phage resistance mutations in the bacterial chromosome. Conjugative plasmids are infectious loops of DNA capable of transmitting DNA between bacterial cells and between species. Because plasmids often carry extra genes that allow bacteria to live in otherwise-inhospitable environments, their dynamics are central to understanding bacterial adaptive evolution. The plasmid-bacterium interaction has typically been studied in isolation, but in natural bacterial communities, bacteriophages, viruses that infect bacteria, are ubiquitous. Using experiments, mathematical models, and computer simulations we show that bacteriophages drive plasmid dynamics through their ecological and evolutionary effects on bacteria and ultimately limit the conditions allowing plasmid existence. These results advance our understanding of bacterial adaptation and show that bacteriophages could be used to select against plasmids carrying undesirable traits, such as antibiotic resistance.
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41
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Abstract
Mobile genetic elements such as plasmids are important for the evolution of prokaryotes. It has been suggested that there are differences between functions coded for by mobile genes and those in the "core" genome and that these differences can be seen between plasmids and chromosomes. In particular, it has been suggested that essential genes, such as those involved in the formation of structural proteins or in basic metabolic functions, are rarely located on plasmids. We model competition between genotypically varying bacteria within a single population to investigate whether selection favors a chromosomal location for essential genes. We find that in general, chromosomal locations for essential genes are indeed favored. This is because the inheritance of chromosomes is more stable than that for plasmids. We define the "degradation" rate as the rate at which chance genetic processes, for example, mutation, deletion, or translocation, render essential genes nonfunctioning. The only way in which plasmids can be a location for functioning essential genes is if chromosomal genes degrade faster than plasmid genes. If the two degradation rates are equal, or if plasmid genes degrade faster than chromosomal genes, functioning essential genes will be found only on chromosomes.
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Affiliation(s)
- Samuel J Tazzyman
- Theoretical Biology, Institute of Integrative Biology (IBZ), ETH Zürich, CH 8092, Zürich, Switzerland
| | - Sebastian Bonhoeffer
- Theoretical Biology, Institute of Integrative Biology (IBZ), ETH Zürich, CH 8092, Zürich, Switzerland
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42
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San Millan A, Peña-Miller R, Toll-Riera M, Halbert ZV, McLean AR, Cooper BS, MacLean RC. Positive selection and compensatory adaptation interact to stabilize non-transmissible plasmids. Nat Commun 2014; 5:5208. [PMID: 25302567 PMCID: PMC4208098 DOI: 10.1038/ncomms6208] [Citation(s) in RCA: 148] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Accepted: 09/10/2014] [Indexed: 12/30/2022] Open
Abstract
Plasmids are important drivers of bacterial evolution, but it is challenging to understand how plasmids persist over the long term because plasmid carriage is costly. Classical models predict that horizontal transfer is necessary for plasmid persistence, but recent work shows that almost half of plasmids are non-transmissible. Here we use a combination of mathematical modelling and experimental evolution to investigate how a costly, non-transmissible plasmid, pNUK73, can be maintained in populations of Pseudomonas aeruginosa. Compensatory adaptation increases plasmid stability by eliminating the cost of plasmid carriage. However, positive selection for plasmid-encoded antibiotic resistance is required to maintain the plasmid by offsetting reductions in plasmid frequency due to segregational loss. Crucially, we show that compensatory adaptation and positive selection reinforce each other’s effects. Our study provides a new understanding of how plasmids persist in bacterial populations, and it helps to explain why resistance can be maintained after antibiotic use is stopped. Plasmids are important for bacterial evolution but the evolutionary mechanisms behind their maintenance are unclear. Here the authors show that the interplay between compensatory adaptation and positive selection for plasmid-encoded antibiotic resistance determines plasmid persistence in P. aeruginosa.
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Affiliation(s)
- A San Millan
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
| | - R Peña-Miller
- 1] Department of Zoology, University of Oxford, Oxford OX1 3PS, UK [2] Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca 62210, México
| | - M Toll-Riera
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
| | - Z V Halbert
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
| | - A R McLean
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
| | - B S Cooper
- 1] Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, Oxford OX3 7BN, UK [2] Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand
| | - R C MacLean
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
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43
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Na G, Zhang W, Zhou S, Gao H, Lu Z, Wu X, Li R, Qiu L, Cai Y, Yao Z. Sulfonamide antibiotics in the Northern Yellow Sea are related to resistant bacteria: implications for antibiotic resistance genes. MARINE POLLUTION BULLETIN 2014; 84:70-75. [PMID: 24928456 DOI: 10.1016/j.marpolbul.2014.05.039] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 05/07/2014] [Accepted: 05/14/2014] [Indexed: 06/03/2023]
Abstract
Antibiotic resistance gene (ARG) residues and the mode of transmission in marine environments remain unclear. The sulfonamide (SAs) concentrations, different genes and total bacterial abundance in seawater and sediment of the Northern Yellow Sea were analyzed. Results showed the genes sul I and sul II were present at relatively high concentrations in all samples, whereas the gene sul III was detected fewer. The ARGs concentrations in the sediment were 10(3) times higher than those in water, which indicated sediment was essential ARG reservoir. Statistical analysis revealed the total antibiotic concentration was positively correlated with the relative abundance of the gene sul I and sul II. The relative abundances of the gene sul I and the gene sul II were also correlated positively with those of the gene int1. This correlation demonstrated that SAs exerted selective pressure on these ARGs, whereas the gene int1 could be implicated in the propagation of the genes sul I and sul II in marine environments.
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Affiliation(s)
- Guangshui Na
- Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian, China; Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
| | - Wanru Zhang
- Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian, China; Dalian Polytechnic University, Dalian, China
| | - Shiyao Zhou
- Dalian Institute of Science and Technology, Dalian, China
| | - Hui Gao
- Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian, China
| | - Zihao Lu
- Dalian Polytechnic University, Dalian, China
| | - Xian Wu
- Dalian Polytechnic University, Dalian, China
| | | | - Lina Qiu
- Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian, China
| | - Yaqi Cai
- Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
| | - Ziwei Yao
- Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian, China
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44
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Tazzyman SJ, Bonhoeffer S. PLASMIDS AND EVOLUTIONARY RESCUE BY DRUG RESISTANCE. Evolution 2014; 68:2066-78. [DOI: 10.1111/evo.12423] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 04/04/2014] [Indexed: 01/21/2023]
Affiliation(s)
- Samuel J. Tazzyman
- Theoretical Biology Group; Institute of Integrative Biology (IBZ); ETH Zürich, Universitätstrasse 16, 8092 Zürich Switzerland
| | - Sebastian Bonhoeffer
- Theoretical Biology Group; Institute of Integrative Biology (IBZ); ETH Zürich, Universitätstrasse 16, 8092 Zürich Switzerland
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45
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Modelling dynamics of plasmid-gene mediated antimicrobial resistance in enteric bacteria using stochastic differential equations. Sci Rep 2014; 3:2463. [PMID: 23982723 PMCID: PMC3755285 DOI: 10.1038/srep02463] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 07/30/2013] [Indexed: 11/25/2022] Open
Abstract
The ubiquitous commensal bacteria harbour genes of antimicrobial resistance (AMR), often on conjugative plasmids. Antimicrobial use in food animals subjects their enteric commensals to antimicrobial pressure. A fraction of enteric Escherichia coli in cattle exhibit plasmid-gene mediated AMR to a third-generation cephalosporin ceftiofur. We adapted stochastic differential equations with diffusion approximation (a compartmental stochastic mathematical model) to research the sources and roles of stochasticity in the resistance dynamics, both during parenteral antimicrobial therapy and in its absence. The results demonstrated that demographic stochasticity among enteric E. coli in the occurrence of relevant events was important for the AMR dynamics only when bacterial numbers were depressed during therapy. However, stochasticity in the parameters of enteric E. coli ecology, whether externally or intrinsically driven, contributed to a wider distribution of the resistant E. coli fraction, both during therapy and in its absence, with stochasticities in individual parameters interacting in their contribution.
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46
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47
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Positive epistasis between co-infecting plasmids promotes plasmid survival in bacterial populations. ISME JOURNAL 2013; 8:601-612. [PMID: 24152711 PMCID: PMC3930321 DOI: 10.1038/ismej.2013.182] [Citation(s) in RCA: 111] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 09/16/2013] [Accepted: 09/17/2013] [Indexed: 11/09/2022]
Abstract
Plasmids have a key role in the horizontal transfer of genes among bacteria. Although plasmids are catalysts for bacterial evolution, it is challenging to understand how they can persist in bacterial populations over the long term because of the burden they impose on their hosts (the ‘plasmid paradox'). This paradox is especially perplexing in the case of ‘small' plasmids, which are unable to self-transfer by conjugation. Here, for the first time, we investigate how interactions between co-infecting plasmids influence plasmid persistence. Using an experimental model system based on interactions between a diverse assemblage of ‘large' plasmids and a single small plasmid, pNI105, in the pathogenic bacterium Pseudomonas aeruginosa, we demonstrate that positive epistasis minimizes the cost associated with carrying multiple plasmids over the short term and increases the stability of the small plasmid over a longer time scale. In support of these experimental data, bioinformatic analysis showed that associations between small and large plasmids are more common than would be expected owing to chance alone across a range of families of bacteria; more generally, we find that co-infection with multiple plasmids is more common than would be expected owing to chance across a wide range of bacterial phyla. Collectively, these results suggest that positive epistasis promotes plasmid stability in bacterial populations. These findings pave the way for future mechanistic studies aimed at elucidating the molecular mechanisms of plasmid–plasmid interaction, and evolutionary studies aimed at understanding how the coevolution of plasmids drives the spread of plasmid-encoded traits.
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48
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Tazzyman SJ, Bonhoeffer S. Fixation probability of mobile genetic elements such as plasmids. Theor Popul Biol 2013; 90:49-55. [PMID: 24080312 DOI: 10.1016/j.tpb.2013.09.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Revised: 09/09/2013] [Accepted: 09/15/2013] [Indexed: 11/17/2022]
Abstract
Mobile genetic elements such as plasmids are increasingly becoming thought of as evolutionarily important. Being horizontally transmissible is generally assumed to be beneficial for a gene. Using several simple modelling approaches we show that in fact being horizontally transferable is just as important for fixation as being beneficial to the host, in line with other results. We find fixation probability is approximately 2(s+β), where s is the increased (vertical) fitness provided by the gene, and β the rate of horizontal transfer when rare. This result comes about because when the gene is rare, almost all individuals in the population are possible recipients of horizontal transfer. The ability to horizontally transfer could thus cause a deleterious gene to become fixed in a population even without hitchhiking. Our findings provide further evidence for the importance and ubiquity of mobile genetic elements, particularly in microorganisms.
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Affiliation(s)
- Samuel J Tazzyman
- Theoretical Biology, Institute of Integrative Biology (INZ), ETH Zürich, CH 8092, Zürich, Switzerland.
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49
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Mc Ginty SÉ, Lehmann L, Brown SP, Rankin DJ. The interplay between relatedness and horizontal gene transfer drives the evolution of plasmid-carried public goods. Proc Biol Sci 2013; 280:20130400. [PMID: 23760639 PMCID: PMC3652439 DOI: 10.1098/rspb.2013.0400] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 04/09/2013] [Indexed: 12/22/2022] Open
Abstract
Plasmids carry a wide range of genes that are often involved in bacterial social behaviour. The question of why such genes are frequently mobile has received increasing attention. Here, we use an explicit population genetic approach to model the evolution of plasmid-borne bacterial public goods production. Our findings highlight the importance of both transmission and relatedness as factors driving the evolution of plasmid-borne public goods production. We partition the effects of plasmid transfer of social traits into those of infectivity and the effect of increased relatedness. Our results demonstrate that, owing to its effect on relatedness, plasmid mobility increases the invasion and stability of public goods, in a way not seen in individually beneficial traits. In addition, we show that plasmid transfer increases relatedness when public goods production is rare but this effect declines when production is common, with both scenarios leading to an increase in the frequency of plasmid-borne public goods. Plasmids remain important vectors for the spread of social genes involved in bacterial virulence thus an understanding of their dynamics is highly relevant from a public health perspective.
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Affiliation(s)
- Sorcha É Mc Ginty
- Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Building Y27, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
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50
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Bao X, Roossinck MJ. A life history view of mutualistic viral symbioses: quantity or quality for cooperation? Curr Opin Microbiol 2013; 16:514-8. [PMID: 23796963 DOI: 10.1016/j.mib.2013.05.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2013] [Revised: 05/27/2013] [Accepted: 05/28/2013] [Indexed: 12/29/2022]
Abstract
Mutualistic symbioses between viruses and their hosts do not employ a straightforward rule by viral genome characteristics, transmission mechanisms or host genotypes. In this review we propose that reproduction rates and environmental carrying capacity of hosts may play a major role in maintaining the mutualism. Depending on how host life history shifts following establishment of the symbiosis, a symbiosis can be classified as quality-selected mutualism or quantity-selected mutualism. Quality-selected mutualism is described with modified Lotka-Volterra models. Both our models and previous empirical examples support the hypothesis that quality-selected mutualism can reach stable equilibrium under certain conditions. Quantity-selected mutualism is rare and is not supported by our model. With increasing attention to mutualistic viral ecology, we will have a better understanding of how viruses drive evolution.
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Affiliation(s)
- Xiaodong Bao
- The Pennsylvania State University, Department of Plant Pathology and Environmental Microbiology, Center for Infectious Disease Dynamics, University Park, PA 16802, United States
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