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Zhang ZJ, Cole CG, Coyne MJ, Lin H, Dylla N, Smith RC, Pappas TE, Townson SA, Laliwala N, Waligurski E, Ramaswamy R, Woodson C, Burgo V, Little JC, Moran D, Rose A, McMillin M, McSpadden E, Sundararajan A, Sidebottom AM, Pamer EG, Comstock LE. Comprehensive analyses of a large human gut Bacteroidales culture collection reveal species- and strain-level diversity and evolution. Cell Host Microbe 2024:S1931-3128(24)00323-8. [PMID: 39293438 DOI: 10.1016/j.chom.2024.08.016] [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: 03/08/2024] [Revised: 06/27/2024] [Accepted: 08/22/2024] [Indexed: 09/20/2024]
Abstract
Species of the Bacteroidales order are among the most abundant and stable bacterial members of the human gut microbiome, with diverse impacts on human health. We cultured and sequenced the genomes of 408 Bacteroidales isolates from healthy human donors representing nine genera and 35 species and performed comparative genomic, gene-specific, metabolomic, and horizontal gene transfer analyses. Families, genera, and species could be grouped based on many distinctive features. We also observed extensive DNA transfer between diverse families, allowing for shared traits and strain evolution. Inter- and intra-species diversity is also apparent in the metabolomic profiling studies. This highly characterized and diverse Bacteroidales culture collection with strain-resolved genomic and metabolomic analyses represents a valuable resource to facilitate informed selection of strains for microbiome reconstitution.
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Affiliation(s)
- Zhenrun J Zhang
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA; Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA
| | - Cody G Cole
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA; Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA
| | - Michael J Coyne
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA; Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA
| | - Huaiying Lin
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Nicholas Dylla
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Rita C Smith
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Téa E Pappas
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Shannon A Townson
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Nina Laliwala
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Emily Waligurski
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA; Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA
| | - Ramanujam Ramaswamy
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Che Woodson
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Victoria Burgo
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Jessica C Little
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - David Moran
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Amber Rose
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Mary McMillin
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Emma McSpadden
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Anitha Sundararajan
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Ashley M Sidebottom
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA
| | - Eric G Pamer
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA; Department of Medicine, Section of Infectious Diseases & Global Health, University of Chicago Medicine, 5841 South Maryland Ave., Chicago, IL 60637, USA; Department of Pathology, University of Chicago Medicine, 5841 South Maryland Ave., Chicago, IL 60637, USA; Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA.
| | - Laurie E Comstock
- Duchossois Family Institute (DFI), University of Chicago, 900 E. 57th St., Chicago, IL 60637, USA; Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA.
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Ali N, Vora C, Mathuria A, Kataria N, Mani I. Advances in CRISPR-Cas systems for gut microbiome. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2024; 208:59-81. [PMID: 39266188 DOI: 10.1016/bs.pmbts.2024.07.008] [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: 09/14/2024]
Abstract
CRISPR-Cas technology has revolutionized microbiome research by enabling precise genetic manipulation of microbial communities. This review explores its diverse applications in gut microbiome studies, probiotic development, microbiome diagnostics, pathogen targeting, and microbial community engineering. Engineered bacteriophages and conjugative probiotics exemplify CRISPR-Cas's capability for targeted bacterial manipulation, offering promising strategies against antibiotic-resistant infections and other gut-related disorders. CRISPR-Cas systems also enhance probiotic efficacy by improving stress tolerance and colonization in the gastrointestinal tract. CRISPR-based techniques in diagnostics enable early intervention by enabling fast and sensitive pathogen identification. Furthermore, CRISPR-mediated gene editing allows tailored modification of microbial populations, mitigating risks associated with horizontal gene transfer and enhancing environmental and health outcomes. Despite its transformative potential, ethical and regulatory challenges loom large, demanding robust frameworks to guide its responsible application. This chapter highlights CRISPR-Cas's pivotal role in advancing microbiome research toward personalized medicine and microbial therapeutics while emphasizing the imperative of balanced ethical deliberations and comprehensive regulatory oversight.
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Affiliation(s)
- Namra Ali
- Department of Microbiology, Gargi College, University of Delhi, New Delhi, India
| | - Chaitali Vora
- Department of Biosciences and Biomedical Engineering, Indian Institute of Technology, Indore, India
| | - Anshu Mathuria
- Department of Biochemistry, Sri Venkateswara College, University of Delhi, New Delhi, India
| | - Naina Kataria
- Department of Biochemistry, Sri Venkateswara College, University of Delhi, New Delhi, India
| | - Indra Mani
- Department of Microbiology, Gargi College, University of Delhi, New Delhi, India.
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Zhang ZJ, Cole CG, Coyne MJ, Lin H, Dylla N, Smith RC, Waligurski E, Ramaswamy R, Woodson C, Burgo V, Little JC, Moran D, Rose A, McMillin M, McSpadden E, Sundararajan A, Sidebottom AM, Pamer EG, Comstock LE. Comprehensive analyses of a large human gut Bacteroidales culture collection reveal species and strain level diversity and evolution. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.08.584156. [PMID: 38496653 PMCID: PMC10942478 DOI: 10.1101/2024.03.08.584156] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Species of the Bacteroidales order are among the most abundant and stable bacterial members of the human gut microbiome with diverse impacts on human health. While Bacteroidales strains and species are genomically and functionally diverse, order-wide comparative analyses are lacking. We cultured and sequenced the genomes of 408 Bacteroidales isolates from healthy human donors representing nine genera and 35 species and performed comparative genomic, gene-specific, mobile gene, and metabolomic analyses. Families, genera, and species could be grouped based on many distinctive features. However, we also show extensive DNA transfer between diverse families, allowing for shared traits and strain evolution. Inter- and intra-specific diversity is also apparent in the metabolomic profiling studies. This highly characterized and diverse Bacteroidales culture collection with strain-resolved genomic and metabolomic analyses can serve as a resource to facilitate informed selection of strains for microbiome reconstitution.
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Affiliation(s)
- Zhenrun J Zhang
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
- Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave, Chicago, IL, 60637, USA
| | - Cody G Cole
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
- Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave, Chicago, IL, 60637, USA
| | - Michael J Coyne
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
- Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave, Chicago, IL, 60637, USA
| | - Huaiying Lin
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Nicholas Dylla
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Rita C Smith
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Emily Waligurski
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
- Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave, Chicago, IL, 60637, USA
| | - Ramanujam Ramaswamy
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Che Woodson
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Victoria Burgo
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Jessica C Little
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - David Moran
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Amber Rose
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Mary McMillin
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Emma McSpadden
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Anitha Sundararajan
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Ashley M Sidebottom
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
| | - Eric G Pamer
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
- Department of Medicine, Section of Infectious Diseases & Global Health, University of Chicago Medicine, 5841 South Maryland Ave, Chicago, IL, 60637, USA
- Department of Pathology, University of Chicago Medicine, 5841 South Maryland Ave, Chicago, IL, 60637, USA
- Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave, Chicago, IL, 60637, USA
| | - Laurie E Comstock
- Duchossois Family Institute, University of Chicago, 900 E. 57th St, Chicago, IL, 60637, USA
- Department of Microbiology, Biological Sciences Division, University of Chicago, 5841 South Maryland Ave, Chicago, IL, 60637, USA
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Vineis JH, Reznikoff WS, Antonopoulos DA, Koval J, Chang E, Fallon BR, Paul BG, Morrison HG, Sogin ML. A novel conjugative transposon carrying an autonomously amplified plasmid. mBio 2024; 15:e0278723. [PMID: 38259081 PMCID: PMC10865816 DOI: 10.1128/mbio.02787-23] [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: 11/02/2023] [Accepted: 11/06/2023] [Indexed: 01/24/2024] Open
Abstract
Tetracyclines serve as broad-spectrum antibiotics to treat bacterial infections. The discovery of new tetracycline resistance genes has led to new questions about the underlying mechanisms of resistance, gene transfer, and their relevance to human health. We tracked changes in the abundance of a 55-kbp conjugative transposon (CTn214) carrying tetQ, a tetracycline resistance gene, within a Bacteroides fragilis metagenome-assembled genome derived from shotgun sequencing of microbial DNA extracted from the ileal pouch of a patient with ulcerative colitis. The mapping of metagenomic reads to CTn214 revealed the multi-copy nature of a 17,044-nt region containing tetQ in samples collected during inflammation and uninflamed visits. B. fragilis cultivars isolated from the same patient during periods of inflammation harbored CTn214 integrated into the chromosome or both a circular, multi-copy, extrachromosomal region of the CTn214 containing tetQ and the corresponding integrated form. The tetracycline-dependent mechanism for the transmission of CTn214 is nearly identical to a common conjugative transposon found in the genome of B. fragilis (CTnDOT), but the autonomously amplified nature of a circular 17,044-nt region of CTn214 that codes for tetQ and the integration of the same sequence in the linear chromosome within the same cell is a novel observation. Genome and transcriptome sequencing of B. fragilis cultivars grown under different concentrations of tetracycline and ciprofloxacin indicates that tetQ in strains containing the circular form remains actively expressed regardless of treatment, while the expression of tetQ in strains containing the linear form increases only in the presence of tetracycline.IMPORTANCEThe exchange of antibiotic production and resistance genes between microorganisms can lead to the emergence of new pathogens. In this study, short-read mapping of metagenomic samples taken over time from the illeal pouch of a patient with ulcerative colitis to a Bacteroides fragilis metagenome-assembled genome revealed two distinct genomic arrangements of a novel conjugative transposon, CTn214, that encodes tetracycline resistance. The autonomous amplification of a plasmid-like circular form from CTn214 that includes tetQ potentially provides consistent ribosome protection against tetracycline. This mode of antibiotic resistance offers a novel mechanism for understanding the emergence of pathobionts like B. fragilis and their persistence for extended periods of time in patients with inflammatory bowel disease.
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Affiliation(s)
- Joseph H. Vineis
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - William S. Reznikoff
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | | | - Jason Koval
- Biosciences Division, Argonne National Laboratory, Argonne, Illinois, USA
| | - Eugene Chang
- Section of Gastroenterology, Department of Medicine, Knapp Center for Biomedical Discovery, The University of Chicago, Chicago, Illinois, USA
| | - Bailey R. Fallon
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Blair G. Paul
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Hilary G. Morrison
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - Mitchell L. Sogin
- Josephine Bay Paul Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA
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Vasco KA, Carbonell S, Sloup RE, Bowcutt B, Colwell RR, Graubics K, Erskine R, Norby B, Ruegg PL, Zhang L, Manning SD. Persistent effects of intramammary ceftiofur treatment on the gut microbiome and antibiotic resistance in dairy cattle. Anim Microbiome 2023; 5:56. [PMID: 37946266 PMCID: PMC10636827 DOI: 10.1186/s42523-023-00274-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Accepted: 10/09/2023] [Indexed: 11/12/2023] Open
Abstract
BACKGROUND Intramammary (IMM) ceftiofur treatment is commonly used in dairy farms to prevent mastitis, though its impact on the cattle gut microbiome and selection of antibiotic-resistant bacteria has not been elucidated. Herein, we enrolled 40 dairy (Holstein) cows at the end of the lactation phase for dry-cow therapy: 20 were treated with IMM ceftiofur (Spectramast®DC) and a non-antibiotic internal teat sealant (bismuth subnitrate) and 20 (controls) received only bismuth subnitrate. Fecal grab samples were collected before and after treatment (weeks 1, 2, 3, 5, 7, and 9) for bacterial quantification and metagenomic next-generation sequencing. RESULTS Overall, 90% and 24% of the 278 samples had Gram-negative bacteria with resistance to ampicillin and ceftiofur, respectively. Most of the cows treated with ceftiofur did not have an increase in the number of resistant bacteria; however, a subset (25%) shed higher levels of ceftiofur-resistant bacteria for up to 2 weeks post-treatment. At week 5, the antibiotic-treated cows had lower microbiota abundance and richness, whereas a greater abundance of genes encoding extended-spectrum β-lactamases (ESBLs), CfxA, ACI-1, and CMY, was observed at weeks 1, 5 and 9. Moreover, the contig and network analyses detected associations between β-lactam resistance genes and phages, mobile genetic elements, and specific genera. Commensal bacterial populations belonging to Bacteroidetes most commonly possessed ESBL genes followed by members of Enterobacteriaceae. CONCLUSION This study highlights variable, persistent effects of IMM ceftiofur treatment on the gut microbiome and resistome in dairy cattle. Antibiotic-treated cattle had an increased abundance of specific taxa and genes encoding ESBL production that persisted for 9 weeks. Fecal shedding of ESBL-producing Enterobacteriaceae, which was classified as a serious public health threat, varied across animals. Together, these findings highlight the need for additional studies aimed at identifying factors associated with shedding levels and the dissemination and persistence of antibiotic resistance determinants on dairy farms across geographic locations.
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Affiliation(s)
- Karla A Vasco
- Department of Microbiology and Molecular Genetics, Michigan State University, E. Lansing, MI, 48824, USA
| | - Samantha Carbonell
- Department of Microbiology and Molecular Genetics, Michigan State University, E. Lansing, MI, 48824, USA
| | - Rebekah E Sloup
- Department of Microbiology and Molecular Genetics, Michigan State University, E. Lansing, MI, 48824, USA
| | - Bailey Bowcutt
- Department of Microbiology and Molecular Genetics, Michigan State University, E. Lansing, MI, 48824, USA
| | - Rita R Colwell
- University of Maryland, Institute for Advanced Computer Studies, College Park, MD, 20742, USA
- Cosmos ID, Inc, Germantown, MD, 20874, USA
| | | | - Ronald Erskine
- Department of Large Animal Clinical Sciences, Michigan State University, E. Lansing, MI, 48824, USA
| | - Bo Norby
- Department of Large Animal Clinical Sciences, Michigan State University, E. Lansing, MI, 48824, USA
| | - Pamela L Ruegg
- Department of Large Animal Clinical Sciences, Michigan State University, E. Lansing, MI, 48824, USA.
| | - Lixin Zhang
- Department of Microbiology and Molecular Genetics, Michigan State University, E. Lansing, MI, 48824, USA.
- Department of Epidemiology and Biostatistics, Michigan State University, E. Lansing, MI, 48824, USA.
| | - Shannon D Manning
- Department of Microbiology and Molecular Genetics, Michigan State University, E. Lansing, MI, 48824, USA.
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Kessler C, Hou J, Neo O, Buckner MMC. In situ, in vivo, and in vitro approaches for studying AMR plasmid conjugation in the gut microbiome. FEMS Microbiol Rev 2022; 47:6807411. [PMID: 36341518 PMCID: PMC9841969 DOI: 10.1093/femsre/fuac044] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 09/23/2022] [Accepted: 11/03/2022] [Indexed: 11/09/2022] Open
Abstract
Antimicrobial resistance (AMR) is a global threat, with evolution and spread of resistance to frontline antibiotics outpacing the development of novel treatments. The spread of AMR is perpetuated by transfer of antimicrobial resistance genes (ARGs) between bacteria, notably those encoded by conjugative plasmids. The human gut microbiome is a known 'melting pot' for plasmid conjugation, with ARG transfer in this environment widely documented. There is a need to better understand the factors affecting the incidence of these transfer events, and to investigate methods of potentially counteracting the spread of ARGs. This review describes the use and potential of three approaches to studying conjugation in the human gut: observation of in situ events in hospitalized patients, modelling of the microbiome in vivo predominantly in rodent models, and the use of in vitro models of various complexities. Each has brought unique insights to our understanding of conjugation in the gut. The use and development of these systems, and combinations thereof, will be pivotal in better understanding the significance, prevalence, and manipulability of horizontal gene transfer in the gut microbiome.
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Affiliation(s)
- Celia Kessler
- Institute of Microbiology and Infection College of Medical and Dental Sciences Biosciences Building University Road West University of Birmingham, B15 2TT, United Kingdom
| | - Jingping Hou
- Institute of Microbiology and Infection College of Medical and Dental Sciences Biosciences Building University Road West University of Birmingham, B15 2TT, United Kingdom
| | - Onalenna Neo
- Institute of Microbiology and Infection College of Medical and Dental Sciences Biosciences Building University Road West University of Birmingham, B15 2TT, United Kingdom
| | - Michelle M C Buckner
- Corresponding author: Biosciences Building, University Road West, University of Birmingham, Birmingham B15 2TT, United Kingdom. Tel: +44 (0)121 415 8758; E-mail:
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Comprehensive investigation of antibiotic resistance gene content in cfiA-harboring Bacteroides fragilis isolates of human and animal origins by whole genome sequencing. Int J Med Microbiol 2022; 312:151559. [PMID: 35961233 DOI: 10.1016/j.ijmm.2022.151559] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Revised: 06/18/2022] [Accepted: 08/07/2022] [Indexed: 11/24/2022] Open
Abstract
INTRODUCTION The emergence of multidrug resistance in Bacteroides fragilis, especially the phylogenetic lineage carrying the carbapenemase gene cfiA, represents an increasing threat to human health. However, knowledge on the diversity of the multidrug-resistant strains and the genetic elements carrying the antibiotic resistance genes (ARGs) remains limited. AIM The objective of the study was to describe the resistome in cfiA-positive B. fragilis. METHODS A collection of cfiA-positive B. fragilis from diverse human (8 bacteremias, 15 wound infections) and animal (2 chickens, 2 pigs, 6 dogs, 3 cats) sources in Hong Kong, 2015-2017 was analysed by whole genome sequencing. RESULTS In the 36 isolates, 13 distinct ARGs (total number 83, median 2, range 0-7 per isolate) other than cfiA were detected. ARGs encoding resistance to aminoglycosides, β-lactams, macrolides, sulphonamides and tetracyclines were carried by CTn341-like, CTnHyb-like, Tn5220-like, Tn4555-like and Tn613-like transposons and were detected in phylogenetically diverse isolates of different host sources. Only few ARGs encoding resistance to metronidazole and tetracyclines were localized on plasmids. In two chicken isolates, a novel transposon (designated as Tn6994) was found to be involved in the dissemination of multiple ARGs mediating resistance to multiple antibiotics, including metronidazole and linezolid that are critically important for treatment of anaerobic infections. In mating experiments, Tn6994 and the associated phenotypic resistance could be transferred to Bacteroides nordii recipient. CONCLUSION This study illustrates the importance of transposons in the dissemination of ARGs in the cfiA-positive division of B. fragilis. One Health approach is necessary to track the dissemination of ARGs.
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Time for Some Group Therapy: Update on Identification, Antimicrobial Resistance, Taxonomy, and Clinical Significance of the Bacteroides fragilis Group. J Clin Microbiol 2022; 60:e0236120. [PMID: 35700139 DOI: 10.1128/jcm.02361-20] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacteroides fragilis group (BFG) species are common members of the human microbiota that provide several benefits to healthy hosts, yet BFG are also the most common anaerobes isolated from human infections, including intra-abdominal infections, abscesses, and bloodstream infection. Compared to many other anaerobes associated with disease, members of the BFG are more likely to be resistant to commonly used antimicrobials, including penicillin (>90% resistant), carbapenems (2 to 20% resistant), and metronidazole (0.2 to 4% resistant). As a result, infection with BFG bacteria can be associated with poor clinical outcomes. Here, we discuss the role of BFG in human health and disease, proposed taxonomic reclassifications within the BFG, and updates in methods for species-level identification. The increasing availability of whole-genome sequencing (WGS) supports recent proposals that the BFG now span two families (Bacteroidaceae and "Tannerellaceae") and multiple genera (Bacteroides, Parabacteroides, and Phocaeicola) within the phylum Bacteroidota. While members of the BFG are often reported to "group" rather than "species" level in many clinical settings, new reports of species-specific trends in antimicrobial resistance profiles and improved resolution of identification tools support routine species-level reporting in clinical practice. Empirical therapy may not be adequate for treatment of serious infections with BFG, warranting susceptibility testing for serious infections. We summarize methods for antimicrobial susceptibility testing and resistance prediction for BFG, including broth microdilution, agar dilution, WGS, and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). We examine global trends in BFG antimicrobial resistance and review genomics of BFG, revealing insights into rapid activation and dissemination of numerous antimicrobial resistance mechanisms.
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Frye KA, Piamthai V, Hsiao A, Degnan PH. Mobilization of vitamin B12 transporters alters competitive dynamics in a human gut microbe. Cell Rep 2021; 37:110164. [PMID: 34965410 PMCID: PMC8759732 DOI: 10.1016/j.celrep.2021.110164] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 06/29/2021] [Accepted: 12/02/2021] [Indexed: 02/07/2023] Open
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The shared resistome of human and pig microbiota is mobilized by distinct genetic elements. Appl Environ Microbiol 2021; 87:AEM.01910-20. [PMID: 33310720 PMCID: PMC8090867 DOI: 10.1128/aem.01910-20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The extensive use of antibiotics in hospitals and in the animal breeding industry has promoted antibiotic resistance in bacteria, which resulted in the emergence of a large number of antibiotic resistance genes in the intestinal tract of human and farmed animals. Genetic exchange of resistance genes between the two ecosystems is now well documented for pathogenic bacteria, but the repertoire of shared resistance genes in the commensal bacterial community and by which genetic modules they are disseminated are still unclear. By analyzing metagenomics data of human and pig intestinal samples both collected in Shenzhen, China, a set of 27 highly prevalent antibiotic resistance genes was found to be shared between human and pig intestinal microbiota. The mobile genetic context for 11 of these core antibiotic resistance genes could be identified by mining their carrying scaffolds constructed from the two datasets, leading to the detection of seven integrative and conjugative/mobilizable elements and two IS-related transposons. The comparison of the relative abundances between these detected mobile genetic elements and their associated antibiotic resistance genes revealed that for many genes, the estimated contribution of the mobile elements to the gene abundance differs strikingly depending on the host. These findings indicate that although some antibiotic resistance genes are ubiquitous across microbiota of human and pig populations, they probably relied on different genetic elements for their dissemination within each population.IMPORTANCE There is growing concern that antibiotic resistance genes could spread from the husbandry environment to human pathogens through dissemination mediated by mobile genetic elements. In this study, we investigated the contribution of mobile genetic elements to the abundance of highly prevalent antibiotic resistance genes found in commensal bacteria of both human and pig intestinal microbiota originating from the same region. Our results reveal that for most of these antibiotic resistance genes, the abundance is not explained by the same mobile genetic element in each host, suggesting that the human and pig microbial communities promoted a different set of mobile genetic carriers for the same antibiotic resistance genes. These results deepen our understanding of the dissemination of antibiotic resistance genes among and between human and pig gut microbiota.
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The uroS and yifB Genes Conserved among Tetrapyrrole Synthesizing-Deficient Bacteroidales Are Involved in Bacteroides fragilis Heme Assimilation and Survival in Experimental Intra-abdominal Infection and Intestinal Colonization. Infect Immun 2020; 88:IAI.00103-20. [PMID: 32457103 DOI: 10.1128/iai.00103-20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 05/15/2020] [Indexed: 01/01/2023] Open
Abstract
The human intestinal anaerobic commensal and opportunistic pathogen Bacteroides fragilis does not synthesize the tetrapyrrole protoporphyrin IX in order to form heme that is required for growth stimulation and survival in vivo Consequently, B. fragilis acquires essential heme from host tissues during extraintestinal infection. The absence of several genes necessary for de novo heme biosynthesis is a common characteristic of many anaerobic bacteria; however, the uroS gene, encoding a uroporphyrinogen III synthase for an early step of heme biosynthesis, is conserved among the heme-requiring Bacteroidales that inhabit the mammalian gastrointestinal tract. In this study, we show that the ability of B. fragilis to utilize heme or protoporphyrin IX for growth was greatly reduced in a ΔuroS mutant. This growth defect appears to be linked to the suppression of reverse chelatase and ferrochelatase activities in the absence of uroS In addition, this ΔuroS suppressive effect was enhanced by the deletion of the yifB gene, which encodes an Mg2+-chelatase protein belonging to the ATPases associated with various cellular activities (AAA+) superfamily of proteins. Furthermore, the ΔuroS mutant and the ΔuroS ΔyifB double mutant had a severe survival defect compared to the parent strain in competitive infection assays using animal models of intra-abdominal infection and intestinal colonization. This shows that the presence of the uroS and yifB genes in B. fragilis seems to be linked to pathophysiological and nutritional competitive fitness for survival in host tissues. Genetic complementation studies and enzyme kinetics assays indicate that B. fragilis UroS is functionally different from canonical bacterial UroS proteins. Taken together, these findings show that heme assimilation and metabolism in the anaerobe B. fragilis have diverged from those of aerobic and facultative anaerobic pathogenic bacteria.
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Jiang X, Hall AB, Arthur TD, Plichta DR, Covington CT, Poyet M, Crothers J, Moses PL, Tolonen AC, Vlamakis H, Alm EJ, Xavier RJ. Invertible promoters mediate bacterial phase variation, antibiotic resistance, and host adaptation in the gut. Science 2019; 363:181-187. [PMID: 30630933 DOI: 10.1126/science.aau5238] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Accepted: 12/03/2018] [Indexed: 12/20/2022]
Abstract
Phase variation, the reversible alternation between genetic states, enables infection by pathogens and colonization by commensals. However, the diversity of phase variation remains underexplored. We developed the PhaseFinder algorithm to quantify DNA inversion-mediated phase variation. A systematic search of 54,875 bacterial genomes identified 4686 intergenic invertible DNA regions (invertons), revealing an enrichment in host-associated bacteria. Invertons containing promoters often regulate extracellular products, underscoring the importance of surface diversity for gut colonization. We found invertons containing promoters regulating antibiotic resistance genes that shift to the ON orientation after antibiotic treatment in human metagenomic data and in vitro, thereby mitigating the cost of antibiotic resistance. We observed that the orientations of some invertons diverge after fecal microbiota transplant, potentially as a result of individual-specific selective forces.
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Affiliation(s)
- Xiaofang Jiang
- Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - A Brantley Hall
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Center for Computational and Integrative Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | | | - Damian R Plichta
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Center for Computational and Integrative Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Christian T Covington
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Center for Computational and Integrative Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Mathilde Poyet
- Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.,Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
| | - Jessica Crothers
- Department of Pathology and Laboratory Medicine, University of Vermont Medical Center, Burlington, VT 05401, USA
| | - Peter L Moses
- Division of Gastroenterology and Hepatology, University of Vermont, Burlington, VT 05401, USA
| | - Andrew C Tolonen
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Center for Computational and Integrative Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Hera Vlamakis
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Center for Computational and Integrative Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
| | - Eric J Alm
- Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. .,Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
| | - Ramnik J Xavier
- Center for Microbiome Informatics and Therapeutics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. .,Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.,Center for Computational and Integrative Biology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.,Gastrointestinal Unit and Center for the Study of Inflammatory Bowel Disease, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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13
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Husain F, Tang K, Veeranagouda Y, Boente R, Patrick S, Blakely G, Wexler HM. Novel large-scale chromosomal transfer in Bacteroides fragilis contributes to its pan-genome and rapid environmental adaptation. Microb Genom 2019; 3. [PMID: 29208130 PMCID: PMC5729914 DOI: 10.1099/mgen.0.000136] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Bacteroides fragilis, an important component of the human gastrointestinal microbiota, can cause lethal extra-intestinal infection upon escape from the gastrointestinal tract. We demonstrated transfer and recombination of large chromosomal segments from B. fragilis HMW615, a multidrug resistant clinical isolate, to B. fragilis 638R. In one example, the transfer of a segment of ~435 Kb/356 genes replaced ~413 Kb/326 genes of the B. fragilis 638R chromosome. In addition to transfer of antibiotic resistance genes, these transfers (1) replaced complete divergent polysaccharide biosynthesis loci; (2) replaced DNA inversion-controlled intergenic shufflons (that control expression of genes encoding starch utilization system outer membrane proteins) with more complex, divergent shufflons; and (3) introduced additional intergenic shufflons encoding divergent Type 1 restriction/modification systems. Conjugative transposon-like genes within a transferred segment and within a putative integrative conjugative element (ICE5) ~45 kb downstream from the transferred segment both encode proteins that may be involved in the observed transfer. These data indicate that chromosomal transfer is a driver of antigenic diversity and nutrient adaptation in Bacteroides that (1) contributes to the dissemination of the extensive B. fragilis pan-genome, (2) allows rapid adaptation to a changing environment and (3) can confer pathogenic characteristics to host symbionts.
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Affiliation(s)
- Fasahath Husain
- Brentwood Biomedical Research Institute, Los Angeles, CA, USA
| | | | | | | | | | | | - Hannah M. Wexler
- Research, GLAVAHCS, 11301 Wilshire Blvd., 691/151J Bldg. 115, Room 312, Los Angeles, CA, USA
- *Correspondence: Hannah M. Wexler,
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14
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Tajkarimi M, Wexler HM. CRISPR-Cas Systems in Bacteroides fragilis, an Important Pathobiont in the Human Gut Microbiome. Front Microbiol 2017; 8:2234. [PMID: 29218031 PMCID: PMC5704556 DOI: 10.3389/fmicb.2017.02234] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2017] [Accepted: 10/31/2017] [Indexed: 12/29/2022] Open
Abstract
Background: While CRISPR-Cas systems have been identified in bacteria from a wide variety of ecological niches, there are no studies to describe CRISPR-Cas elements in Bacteroides species, the most prevalent anaerobic bacteria in the lower intestinal tract. Microbes of the genus Bacteroides make up ~25% of the total gut microbiome. Bacteroides fragilis comprises only 2% of the total Bacteroides in the gut, yet causes of >70% of Bacteroides infections. The factors causing it to transition from benign resident of the gut microbiome to virulent pathogen are not well understood, but a combination of horizontal gene transfer (HGT) of virulence genes and differential transcription of endogenous genes are clearly involved. The CRISPR-Cas system is a multi-functional system described in prokaryotes that may be involved in control both of HGT and of gene regulation. Results: Clustered regularly interspaced short palindromic repeats (CRISPR) elements in all strains of B. fragilis (n = 109) with publically available genomes were identified. Three different CRISPR-Cas types, corresponding most closely to Type IB, Type IIIB, and Type IIC, were identified. Thirty-five strains had two CRISPR-Cas types, and three strains included all three CRISPR-Cas types in their respective genomes. The cas1 gene in the Type IIIB system encoded a reverse-transcriptase/Cas1 fusion protein rarely found in prokaryotes. We identified a short CRISPR (3 DR) with no associated cas genes present in most of the isolates; these CRISPRs were found immediately upstream of a hipA/hipB operon and we speculate that this element may be involved in regulation of this operon related to formation of persister cells during antimicrobial exposure. Also, blood isolates of B. fragilis did not have Type IIC CRISPR-Cas systems and had atypical Type IIIB CRISPR-Cas systems that were lacking adjacent cas genes. Conclusions: This is the first systematic report of CRISPR-Cas systems in a wide range of B. fragilis strains from a variety of sources. There are four apparent CRISPR-Cas systems in B. fragilis-three systems have adjacent cas genes. Understanding CRISPR/Cas function in B. fragilis will elucidate their role in gene expression, DNA repair and ability to survive exposure to antibiotics. Also, based on their unique CRISPR-Cas arrays, their phylogenetic clustering and their virulence potential, we are proposing that blood isolates of B. fragilis be viewed a separate subgroup.
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Affiliation(s)
- Mehrdad Tajkarimi
- Brentwood Biomedical Research Institute, Los Angeles, CA, United States
| | - Hannah M. Wexler
- Brentwood Biomedical Research Institute, Los Angeles, CA, United States
- University of California, Los Angeles, Los Angeles, CA, United States
- GLAVA Health Care System, Los Angeles, CA, United States
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15
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Abstract
UNLABELLED Antibiotic resistance is a worldwide health risk, but the influence of animal agriculture on the genetic context and enrichment of individual antibiotic resistance alleles remains unclear. Using quantitative PCR followed by amplicon sequencing, we quantified and sequenced 44 genes related to antibiotic resistance, mobile genetic elements, and bacterial phylogeny in microbiomes from U.S. laboratory swine and from swine farms from three Chinese regions. We identified highly abundant resistance clusters: groups of resistance and mobile genetic element alleles that cooccur. For example, the abundance of genes conferring resistance to six classes of antibiotics together with class 1 integrase and the abundance of IS6100-type transposons in three Chinese regions are directly correlated. These resistance cluster genes likely colocalize in microbial genomes in the farms. Resistance cluster alleles were dramatically enriched (up to 1 to 10% as abundant as 16S rRNA) and indicate that multidrug-resistant bacteria are likely the norm rather than an exception in these communities. This enrichment largely occurred independently of phylogenetic composition; thus, resistance clusters are likely present in many bacterial taxa. Furthermore, resistance clusters contain resistance genes that confer resistance to antibiotics independently of their particular use on the farms. Selection for these clusters is likely due to the use of only a subset of the broad range of chemicals to which the clusters confer resistance. The scale of animal agriculture and its wastes, the enrichment and horizontal gene transfer potential of the clusters, and the vicinity of large human populations suggest that managing this resistance reservoir is important for minimizing human risk. IMPORTANCE Agricultural antibiotic use results in clusters of cooccurring resistance genes that together confer resistance to multiple antibiotics. The use of a single antibiotic could select for an entire suite of resistance genes if they are genetically linked. No links to bacterial membership were observed for these clusters of resistance genes. These findings urge deeper understanding of colocalization of resistance genes and mobile genetic elements in resistance islands and their distribution throughout antibiotic-exposed microbiomes. As governments seek to combat the rise in antibiotic resistance, a balance is sought between ensuring proper animal health and welfare and preserving medically important antibiotics for therapeutic use. Metagenomic and genomic monitoring will be critical to determine if resistance genes can be reduced in animal microbiomes, or if these gene clusters will continue to be coselected by antibiotics not deemed medically important for human health but used for growth promotion or by medically important antibiotics used therapeutically.
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Thiemann S, Smit N, Strowig T. Antibiotics and the Intestinal Microbiome : Individual Responses, Resilience of the Ecosystem, and the Susceptibility to Infections. Curr Top Microbiol Immunol 2016; 398:123-146. [PMID: 27738912 DOI: 10.1007/82_2016_504] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The intestinal microbiota is a diverse ecosystem containing thousands of microbial species, whose metabolic activity affects many aspects of human physiology. Large-scale surveys have demonstrated that an individual's microbiota composition is shaped by factors such as diet and the use of medications, including antibiotics. Loss of overall diversity and in some cases loss of single groups of bacteria as a consequence of antibiotic treatment in humans has been associated with enhanced susceptibility toward gastrointestinal infections and with enhanced weight gain and obesity in young children. Moreover, the extensive use of antibiotics has led to an increased abundance of antibiotic resistance genes (ARGs) within commensal bacteria that can be transferred to invading pathogens, which complicates the treatment of bacterial infections. In this review, we provide insight into the complex interplay between the microbiota and antibiotics focussing on (i) the effect of antibiotics on the composition of the microbiota, (ii) the impact of antibiotics on gastrointestinal infections, and (iii) finally the role of the microbiota as reservoir for ARGs. We also discuss how targeted manipulation of the microbiota may be used as an innovative therapeutic approach to reduce the incidence of bacterial infections as well as resulting complications.
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Affiliation(s)
| | - Nathiana Smit
- Helmholtz Centre for Infection Research, Brunswick, Germany
| | - Till Strowig
- Helmholtz Centre for Infection Research, Brunswick, Germany.
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Li XZ, Plésiat P, Nikaido H. The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria. Clin Microbiol Rev 2015; 28:337-418. [PMID: 25788514 PMCID: PMC4402952 DOI: 10.1128/cmr.00117-14] [Citation(s) in RCA: 924] [Impact Index Per Article: 102.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The global emergence of multidrug-resistant Gram-negative bacteria is a growing threat to antibiotic therapy. The chromosomally encoded drug efflux mechanisms that are ubiquitous in these bacteria greatly contribute to antibiotic resistance and present a major challenge for antibiotic development. Multidrug pumps, particularly those represented by the clinically relevant AcrAB-TolC and Mex pumps of the resistance-nodulation-division (RND) superfamily, not only mediate intrinsic and acquired multidrug resistance (MDR) but also are involved in other functions, including the bacterial stress response and pathogenicity. Additionally, efflux pumps interact synergistically with other resistance mechanisms (e.g., with the outer membrane permeability barrier) to increase resistance levels. Since the discovery of RND pumps in the early 1990s, remarkable scientific and technological advances have allowed for an in-depth understanding of the structural and biochemical basis, substrate profiles, molecular regulation, and inhibition of MDR pumps. However, the development of clinically useful efflux pump inhibitors and/or new antibiotics that can bypass pump effects continues to be a challenge. Plasmid-borne efflux pump genes (including those for RND pumps) have increasingly been identified. This article highlights the recent progress obtained for organisms of clinical significance, together with methodological considerations for the characterization of MDR pumps.
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Affiliation(s)
- Xian-Zhi Li
- Human Safety Division, Veterinary Drugs Directorate, Health Products and Food Branch, Health Canada, Ottawa, Ontario, Canada
| | - Patrick Plésiat
- Laboratoire de Bactériologie, Faculté de Médecine-Pharmacie, Centre Hospitalier Régional Universitaire, Université de Franche-Comté, Besançon, France
| | - Hiroshi Nikaido
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
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18
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Identification of antimicrobial resistance genes in multidrug-resistant clinical Bacteroides fragilis isolates by whole genome shotgun sequencing. Anaerobe 2015; 31:59-64. [DOI: 10.1016/j.anaerobe.2014.10.009] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 09/29/2014] [Accepted: 10/31/2014] [Indexed: 11/22/2022]
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