Antimicrobial resistance acquisition via natural transformation: context is everything

Analysis of antibiotic resistance genes in livestock manure and receiving environment reveals non-negligible risk from extracellular genes

Antibiotic resistance genes (ARGs), extracellular and intracellular, collectively constitute the complete resistome within farming environments. However, a systematic analysis of extracellular ARGs (eARGs) and intracellular ARGs (iARGs) remains missing. This study characterized eARGs and iARGs in livestock manure and examined their effects on the agricultural soil receiving them. The findings indicated differences in DNA concentration and the ratios of iDNA and eDNA across various manures, with chicken manure demonstrating the highest eDNA levels (20.7-22.7%). Different ARG subtypes had distinct pollution levels in livestock manure. Generally, except for blaTEM-1 and blaOXA-1, ermC, ermB, and cfr, other ARGs were abundant in eDNA (beyond 104 copies per g DW in each sample) and iDNA (beyond 107 copies per g DW) of animal manure. The copy numbers of eARGs and iARGs differed in different manures, with swine manure having the highest, ranging from 6.08 × 103 to 4.30 × 108 and from 3.21 × 107 to 9.51 × 1010 copies per g DW, respectively. Both iARGs and eARGs were more abundant in soil when manure was applied. The impacts of the various manures varied, with chicken manure having the most significant influence. Interestingly, several eARGs were much more abundant in soil than their intracellular counterparts, highlighting the need to regulate and manage both eARGs and iARGs.

Plastic-mediated transformation: A new route to navigate plasmid-borne antibiotic resistance genes

Among the anthropogenic sources of pollution, accumulation of plastic polymers in aquatic ecosystems is scaling at unprecedented rates and emerging as a new niche for bacterial colonization and horizontal gene transfer (HGT). The current study focuses on determining the ability of bacteria to acquire plasmid DNA from the extracellular environment under exposure to different treatments (soil, CaCl2 salt solution, soil plus CaCl2, Escherichia coli cell-free extract, and plastic debris) that simulate possible conditions experienced by microorganisms in natural environments. The transformation frequency of two plasmids (pACYC:Hyg and pBAV-1k) was tested following two experimental approaches: single species microcosm of E. coli cells (SSM) and bacterial consortium microcosm (BCM) of strains isolated from freshwater ecosystems. Plastic fragments (with consistent results obtained using polypropylene) proved to be remarkably efficient in increasing the bacterial competence towards plasmid DNA uptake as compared to the other conditions. Moreover, the effects of different plastic polymers and four incubation conditions on bacterial DNA transformation were analyzed to gain deeper insight into the exchange of genetic material. Our findings from both experimental approaches demonstrate that simultaneous incubation of microorganisms, plasmids, and plastic fragments enhances the bacterial ability to uptake plasmids and to express genes required for survival under stress conditions. The two microcosm models prove to be promising tools to mimic natural transformation events leading to the dissemination of antibiotic-resistant genes via HGT in the environment.

pH-gated activation of nematodes-secreted NUC-1 accelerates extracellular antibiotic resistance gene degradation in aquatic environments

The global dissemination of extracellular antibiotic resistance genes (eARGs) in environmental matrices necessitates urgent development of mitigation approaches. Although nematodes exhibit potential as biological agents for eARG degradation, significant research gaps exist in understanding their performance under diverse environmental conditions and strategies for enhancing degradation efficiency through systematic parameter optimization. Here, we systematically evaluated the degradation of plasmid-borne tetM by Caenorhabditis elegans across eight high nematodes-prevalent habitats, revealing a remarkable 38-fold variation in efficacy. Solution pH was identified as the pivotal regulatory parameter through controlled experiments. Acidification to pH 6 enhanced nematodes-mediated eARG degradation by 25-fold, effectively reducing the transformation efficiency below the detectable limit within 15 min. Through multidisciplinary analyses incorporating gene mutation analysis, mRNA quantification, capillary electrophoresis, and zymographic analysis, we demonstrate that environmental pH specifically modulates NUC-1 activity rather than expression. Structural modeling and pKa calculation reveal this pH-dependent regulation operates through protonation state change in the NUC-1 catalytic center, achieving maximal enzymatic activity at pH 6. Remarkably, this pH-gated regulatory mechanism is conserved across five nematode species spanning two distinct families, highlighting its broad biological significance and biotechnological potential. Our study establishes the first comprehensive environmental assessment framework for nematodes-mediated eARG degradation and elucidates a pH-gated regulation mechanism at the molecular level, providing a novel foundation for developing biotechnologies to control AR dissemination with spatiotemporal accuracy.

Enterococci for human health: A friend or foe?

Enterococci are widely distributed in nature and exhibit good temperature and pH tolerance, making them suitable for industrial fermentation. It can produce bacteriocins, natural antibacterial substances utilized in food preservation. Some Enterococci are employed as probiotics to regulate human immunity and maintain healthy intestinal environments. However, recent scientific studies have highlighted the pathogenicity and multidrug resistance of Enterococci, classifying it as an important pathogen in clinical infections. Moreover, increasing evidence has linked Enterococcus sp., particularly Enterococcus faecalis and Enterococcus faecium, to clinical diseases, raising concerns about their safety and posing the question, how should we approach the conflicting nature of the pathogenic and beneficial effects of Enterococci? This review provides the recent advancements in Enterococci research and incorporates the perspectives of international authoritative organizations and institutions to comprehensively analyze the beneficial and harmful characteristics of Enterococci in the fields of science, clinical and industrial applications, aiming to address three important questions: whether Enterococci are beneficial or harmful to humans, their potential use in medical treatments, and the criteria to evaluate their safety. The goal is to explore the feasibility of the standardized use of Enterococci and provide guidance on the scientific selection and utilization of probiotics.

Jellyfish blooms-an overlooked hotspot and potential vector for the transmission of antimicrobial resistance in marine environments

Gelatinous zooplankton (GZ) represents an important component of marine food webs, capable of generating massive blooms with severe environmental impact. When these blooms collapse, considerable amounts of organic matter (GZ-OM) either sink to the seafloor or can be introduced into the ocean's interior, promoting bacterial growth and providing a colonizable surface for microbial interactions. We hypothesized that GZ-OM is an overlooked marine hotspot for transmitting antimicrobial resistance genes (ARGs). To test this, we first re-analyzed metagenomes from two previous studies that experimentally evolved marine microbial communities in the presence and absence of OM from Aurelia aurita and Mnemiopsis leidyi recovered from bloom events and thereafter performed additional time-resolved GZ-OM degradation experiments to improve sample size and statistical power of our analysis. We analyzed these communities for composition, ARG, and mobile genetic element (MGE) content. Communities exposed to GZ-OM displayed up to fourfold increased relative ARG and up to 10-fold increased MGE abundance per 16S rRNA gene copy compared to the controls. This pattern was consistent across ARG and MGE classes and independent of the GZ species, indicating that nutrient influx and colonizable surfaces drive these changes. Potential ARG carriers included genera containing potential pathogens raising concerns of ARG transfer to pathogenic strains. Vibrio was pinpointed as a key player associated with elevated ARGs and MGEs. Whole-genome sequencing of a Vibrio isolate revealed the genetic capability for ARG mobilization and transfer. This study establishes the first link between two emerging issues of marine coastal zones, jellyfish blooms and ARG spread, both likely increasing with future ocean change. Hence, jellyfish blooms are a quintessential "One Health" issue where decreasing environmental health directly impacts human health.IMPORTANCEJellyfish blooms are, in the context of human health, often seen as mainly problematic for oceanic bathing. Here we demonstrate that they may also play a critical role as marine environmental hotspots for the transmission of antimicrobial resistance (AMR). This study employed (re-)analyses of microcosm experiments to investigate how particulate organic matter introduced to the ocean from collapsed jellyfish blooms, specifically Aurelia aurita and Mnemiopsis leidyi, can significantly increase the presence of antimicrobial resistance genes and mobile genetic elements in marine microbial communities by up to one order of magnitude. By providing abundant nutrients and surfaces for bacterial colonization, organic matter from these blooms enhances ARG proliferation, including transfer to and mobility in potentially pathogenic bacteria like Vibrio. Understanding this connection highlights the importance of monitoring jellyfish blooms as part of marine health assessments and developing strategies to mitigate the spread of AMR in coastal ecosystems.

Genetic compatibility and ecological connectivity drive the dissemination of antibiotic resistance genes

The dissemination of mobile antibiotic resistance genes (ARGs) via horizontal gene transfer is a significant threat to public health globally. The flow of ARGs into and between pathogens, however, remains poorly understood, limiting our ability to develop strategies for managing the antibiotic resistance crisis. Therefore, we aim to identify genetic and ecological factors that are fundamental for successful horizontal ARG transfer. We used a phylogenetic method to identify instances of horizontal ARG transfer in ~1 million bacterial genomes. This data was then integrated with >20,000 metagenomes representing animal, human, soil, water, and wastewater microbiomes to develop random forest models that can reliably predict horizontal ARG transfer between bacteria. Our results suggest that genetic incompatibility, measured as nucleotide composition dissimilarity, negatively influences the likelihood of transfer of ARGs between evolutionarily divergent bacteria. Conversely, environmental co-occurrence increases the likelihood, especially in humans and wastewater, in which several environment-specific dissemination patterns are observed. This study provides data-driven ways to predict the spread of ARGs and provides insights into the mechanisms governing this evolutionary process.

The Spread of Antibiotic Resistance Is Driven by Plasmids Among the Fastest Evolving and of Broadest Host Range

Microorganisms endure novel challenges for which other microorganisms in other biomes may have already evolved solutions. This is the case of nosocomial bacteria under antibiotic therapy because antibiotics are of ancient natural origin and resistances to them have previously emerged in environmental bacteria. In such cases, the rate of adaptation crucially depends on the acquisition of genes by horizontal transfer of plasmids from distantly related bacteria in different biomes. We hypothesized that such processes should be driven by plasmids among the most mobile and evolvable. We confirmed these predictions by showing that plasmid species encoding antibiotic resistance are very mobile, have broad host ranges, while showing higher rates of homologous recombination and faster turnover of gene repertoires than the other plasmids. These characteristics remain outstanding when we remove resistance plasmids from our dataset, suggesting that antibiotic resistance genes are preferentially acquired and carried by plasmid species that are intrinsically very mobile and plastic. Evolvability and mobility facilitate the transfer of antibiotic resistance, and presumably of other phenotypes, across distant taxonomic groups and biomes. Hence, plasmid species, and possibly those of other mobile genetic elements, have differentiated and predictable roles in the spread of novel traits.

Neglected contributors to the transmission of bacterial antibiotic resistance in drinking water: Extracellular antibiotic resistance genes and the natural transformation

Antibiotic resistance genes (ARGs) have increasingly gained recognition as an "emerging contaminant" that poses a threat to the biosafety of drinking water. However, previous researches have primarily focused on the intracellular state of ARGs and rarely investigated the ecological characteristics (e.g., distribution and origin), environmental behavior (spread), and risks of extracellular form (eARGs) within drinking water systems. Therefore, this review evaluated isolation strategies and extraction methods for recovering eARGs from drinking water, elucidated the distribution characteristics of eARGs, and examined their impact on the antibiotic resistome from source water to tap water. We emphasized that chlorination and biological treatments significantly contribute to the prevalence and persistence of eARGs in drinking water. Moreover, we highlighted the role of biological reactors (e.g., biofilter, biological activated carbon) and drinking water distribution systems in facilitating the natural transformation of eARGs while significantly contributing to bacterial antibiotic resistance (BAR) propagation. Finally, we summarized the current risk assessment systems for ARGs and critically address remaining challenging questions necessary for better forecasting health risks associated with eARGs in drinking water environments. Collectively, this review enhances the understanding of ecological characteristics and environmental behavior of eARGs in drinking water while providing important implications for controlling and reducing BAR contamination not only in drinking water but also in other aquatic environments.

The role of bacteriophages in facilitating the horizontal transfer of antibiotic resistance genes in municipal wastewater treatment plants

Bacteriophages play integral roles in the ecosystem; however, their precise involvement in horizontal gene transfer and the spread of antibiotic resistance genes (ARGs) are not fully understood. In this study, a coculture system involving consortia of bacteriophages and multidrug-resistant bacteria from an aerobic tank in a municipal wastewater treatment plant (WWTP) was established to investigate the functions of bacteriophages in ARG transfer and spread. The results of the cocultivation of the MRB and bacteriophage consortia indicated that the bacterial community remained stable throughout the whole process, but the addition of bacteriophages significantly increased ARG abundance, especially in bacteriophage DNA. Nine out of the 11 identified ARGs significantly increased, indicating that more bacteriophage particles carried ARGs in the system after cocultivation. In addition, 686 plasmids were detected during cocultivation, of which only 3.36 % were identified as conjugative plasmids, which is significantly lower than the proportion found among previously published plasmids (25.2 %, totaling 14,029 plasmids). Our findings revealed that bacteriophages may play important roles in the horizontal transfer of ARGs through both bacteriophage-mediated conduction and an increase in extracellular ARGs; however, conjugative transfer may not be the main mechanism by which multidrug-resistant bacteria acquire and spread ARGs. Unlike in most previous reports, a coculture system of diverse bacteria and bacteriophages was established in this study to assess bacteriophage functions in ARG transfer and dissemination in the environment, overcoming the limitations associated with the isolation of bacteria and bacteriophages, as well as the specificity of bacteriophage hosts.

Non-antibiotic compounds associated with humans and the environment can promote horizontal transfer of antimicrobial resistance genes

Horizontal gene transfer plays a key role in the global dissemination of antimicrobial resistance (AMR). AMR genes are often carried on self-transmissible plasmids, which are shared amongst bacteria primarily by conjugation. Antibiotic use has been a well-established driver of the emergence and spread of AMR. However, the impact of commonly used non-antibiotic compounds and environmental pollutants on AMR spread has been largely overlooked. Recent studies found common prescription and over-the-counter drugs, artificial sweeteners, food preservatives, and environmental pollutants, can increase the conjugative transfer of AMR plasmids. The potential mechanisms by which these compounds promote plasmid transmission include increased membrane permeability, upregulation of plasmid transfer genes, formation of reactive oxygen species, and SOS response gene induction. Many questions remain around the impact of most non-antibiotic compounds on AMR plasmid conjugation in clinical isolates and the long-term impact on AMR dissemination. By elucidating the role of routinely used pharmaceuticals, food additives, and pollutants in the dissemination of AMR, action can be taken to mitigate their impact by closely monitoring use and disposal. This review will discuss recent progress on understanding the influence of non-antibiotic compounds on plasmid transmission, the mechanisms by which they promote transfer, and the level of risk they pose.

An Overview of the Recent Advances in Antimicrobial Resistance

Antimicrobial resistance (AMR), frequently considered a major global public health threat, requires a comprehensive understanding of its emergence, mechanisms, advances, and implications. AMR's epidemiological landscape is characterized by its widespread prevalence and constantly evolving patterns, with multidrug-resistant organisms (MDROs) creating new challenges every day. The most common mechanisms underlying AMR (i.e., genetic mutations, horizontal gene transfer, and selective pressure) contribute to the emergence and dissemination of new resistant strains. Therefore, mitigation strategies (e.g., antibiotic stewardship programs-ASPs-and infection prevention and control strategies-IPCs) emphasize the importance of responsible antimicrobial use and surveillance. A One Health approach (i.e., the interconnectedness of human, animal, and environmental health) highlights the necessity for interdisciplinary collaboration and holistic strategies in combating AMR. Advancements in novel therapeutics (e.g., alternative antimicrobial agents and vaccines) offer promising avenues in addressing AMR challenges. Policy interventions at the international and national levels also promote ASPs aiming to regulate antimicrobial use. Despite all of the observed progress, AMR remains a pressing concern, demanding sustained efforts to address emerging threats and promote antimicrobial sustainability. Future research must prioritize innovative approaches and address the complex socioecological dynamics underlying AMR. This manuscript is a comprehensive resource for researchers, policymakers, and healthcare professionals seeking to navigate the complex AMR landscape and develop effective strategies for its mitigation.

Mechanism of antibacterial resistance, strategies and next-generation antimicrobials to contain antimicrobial resistance: a review

Antibacterial drug resistance poses a significant challenge to modern healthcare systems, threatening our ability to effectively treat bacterial infections. This review aims to provide a comprehensive overview of the types and mechanisms of antibacterial drug resistance. To achieve this aim, a thorough literature search was conducted to identify key studies and reviews on antibacterial resistance mechanisms, strategies and next-generation antimicrobials to contain antimicrobial resistance. In this review, types of resistance and major mechanisms of antibacterial resistance with examples including target site modifications, decreased influx, increased efflux pumps, and enzymatic inactivation of antibacterials has been discussed. Moreover, biofilm formation, and horizontal gene transfer methods has also been included. Furthermore, measures (interventions) taken to control antimicrobial resistance and next-generation antimicrobials have been discussed in detail. Overall, this review provides valuable insights into the diverse mechanisms employed by bacteria to resist the effects of antibacterial drugs, with the aim of informing future research and guiding antimicrobial stewardship efforts.

Anthropogenic pollution may enhance natural transformation in water, favouring the spread of antibiotic resistance genes

Aquatic ecosystems are crucial in the antimicrobial resistance cycle. While intracellular DNA has been extensively studied to understand human activity's impact on antimicrobial resistance gene (ARG) dissemination, extracellular DNA is frequently overlooked. This study examines the effect of anthropogenic water pollution on microbial community diversity, the resistome, and ARG dissemination. We analyzed intracellular and extracellular DNA from wastewater treatment plant effluents and lake surface water by shotgun sequencing. We also conducted experiments to evaluate anthropogenic pollution's effect on transforming extracellular DNA (using Gfp-plasmids carrying ARGs) within a natural microbial community. Chemical analysis showed treated wastewater had higher anthropogenic pollution-related parameters than lake water. The richness of microbial community, antimicrobial resistome, and high-risk ARGs was greater in treated wastewaters than in lake waters both for intracellular and extracellular DNA. Except for the high-risk ARGs, richness was significantly higher in intracellular than in extracellular DNA. Several ARGs were associated with mobile genetic elements and located on plasmids. Furthermore, Gfp-plasmid transformation within a natural microbial community was enhanced by anthropogenic pollution levels. Our findings underscore anthropogenic pollution's pivotal role in shaping microbial communities and their antimicrobial resistome. Additionally, it may facilitate ARG dissemination through extracellular DNA plasmid uptake.

ComI inhibits transformation in Bacillus subtilis by selectively killing competent cells

Many bacteria build elaborate molecular machines to import DNA via natural competence, yet this activity is often not identified until strains have been handled and domesticated in laboratory settings. For example, one of the best studied Gram-positive model organisms, Bacillus subtilis, has a poorly transformable ancestor. Transformation in the ancestral strain is inhibited by a transmembrane peptide, ComI, which is encoded on an extrachromosomal plasmid. Although ComI was shown to be necessary and sufficient to inhibit transformation when produced at high levels under an inducible promoter, the mechanism by which ComI inhibits transformation is unknown. Here, we examine the native regulation and mechanism of transformation inhibition by ComI. We find that under native regulation, ComI expression is restricted in the absence of the plasmid. In the presence of the plasmid, we find that ComI is expressed at higher levels in cells that are differentiating into a competent state. The subcellular localization of ComI, however, does not depend on any other competence proteins, and permeabilization activity is concentration-dependent. Time-lapse microscopy reveals that competent cells producing ComI are first permeabilized and then die. Based on these observations, we propose a new model for the mechanism of ComI in which response to competence activation leads to selective elimination of the competent subpopulation.

IMPORTANCE

Natural transformation mechanisms have been studied across several bacterial systems, but few examples of inhibition exist. This work investigates the mechanism of action of a plasmid-encoded transmembrane inhibitor of natural transformation. The data reveal that the peptide can cause cell permeabilization. Permeabilization is synergistic with entry of Bacillus subtilis into the "competent" state, such that cells with the ability to be transformed are preferentially killed. These findings reveal a self-preservation mechanism coupled to the physiological state of the cells that ensures that the population can maintain an unaltered plasmid and its predicted prophage.

Effect of chemotherapeutic agents on natural transformation frequency in Acinetobacter baylyi

Natural transformation is the ability of a bacterial cell to take up extracellular DNA which is subsequently available for recombination into the chromosome (or maintenance as an extrachromosomal element). Like other mechanisms of horizontal gene transfer, natural transformation is a significant driver for the dissemination of antimicrobial resistance. Recent studies have shown that many pharmaceutical compounds such as antidepressants and anti-inflammatory drugs can upregulate transformation frequency in the model species Acinetobacter baylyi. Chemotherapeutic compounds have been shown to increase the abundance of antimicrobial resistance genes and increase colonization rates of potentially pathogenic bacteria in patient gastrointestinal tracts, indicating an increased risk of infection and providing a pool of pathogenicity or resistance genes for transformable commensal bacteria. We here test for the effect of six cancer chemotherapeutic compounds on A. baylyi natural transformation frequency, finding two compounds, docetaxel and daunorubicin, to significantly decrease transformation frequency, and daunorubicin to also decrease growth rate significantly. Enhancing our understanding of the effect of chemotherapeutic compounds on the frequency of natural transformation could aid in preventing the horizontal spread of antimicrobial resistance genes.

RATA: A novel class A carbapenemase with broad geographic distribution and potential for global spread

Carbapenem resistance's global proliferation poses a significant public health challenge. The primary resistance mechanism is carbapenemase production. In this study, we discovered a novel carbapenemase, RATA, located on the chromosome of Riemerella anatipestifer isolates. This enzyme shares ≤52 % amino acid sequence identity with other known β-lactamases. Antimicrobial susceptibility tests and kinetic assays demonstrated that RATA could hydrolyze not only penicillins and extended-spectrum cephalosporins but also monobactams, cephamycins, and carbapenems. Furthermore, its activity was readily inhibited by β-lactamase inhibitors. Bioinformatic analysis revealed 46 blaRATA-like genes encoding 27 variants in the NCBI database, involving 21 different species, including pathogens, host-associated bacteria, and environmental isolates. Notably, blaRATA-positive strains were globally distributed and primarily collected from marine environments. Concurrently, taxonomic analysis and GC content analysis indicated that blaRATA orthologue genes were predominantly located on the chromosomes of Flavobacteriaceae and shared a similar GC content as Flavobacteriaceae. Although no explicit mobile genetic elements were identified by genetic environment analysis, blaRATA-2 possessed the ability of horizontal transfer in R. anatipestifer via natural transformation. This work's data suggest that RATA is a new chromosome-encoded class A carbapenemase, and Flavobacteriaceae from marine environments could be the primary reservoir of the blaRATA gene.

DNA binding is rate-limiting for natural transformation

Bacteria take up environmental DNA using dynamic appendages called type IV pili (T4P) to elicit horizontal gene transfer in a process called natural transformation. Natural transformation is widespread amongst bacteria yet determining how different factors universally contribute to or limit this process across species has remained challenging. Here we show that Acinetobacter baylyi, the most naturally transformable species, is highly transformable due to its ability to robustly bind nonspecific DNA via a dedicated orphan minor pilin, FimT. We show that, compared to its homologues, A. baylyi FimT contains multiple positively charged residues that additively promote DNA binding efficiency. Expression of A. baylyi FimT in a closely related Acinetobacter pathogen is sufficient to substantially improve its capacity for natural transformation, demonstrating that T4P-DNA binding is a rate-limiting step in this process. These results demonstrate the importance of T4P-DNA binding efficiency in driving natural transformation, establishing a key factor limiting horizontal gene transfer.

A Broad-Spectrum Horizontal Transfer Inhibitor Prevents Transmission of Plasmids Carrying Multiple Antibiotic Resistance Genes

The dissemination of antimicrobial resistance (AMR) severely degrades the performance of antibiotics and constantly paralyzes the global health system. In particular, plasmid-mediated transfer of antibiotic resistance genes (ARGs) across bacteria is recognized as the primary driver. Therefore, antiplasmid transfer approaches are urgently warranted to resolve this intractable problem. Herein, we demonstrated the potential of azidothymidine (AZT), an FDA-approved anti-HIV drug, as a broad-spectrum horizontal transfer inhibitor to effectively prevent the transmission of multiple ARGs, including mcr-1, bla NDM-5, and tet(X4), both in vitro and in vivo. It was also noteworthy that the inhibitory effect of AZT was proved to be valid within and across bacterial genera under different mating conditions. Mechanistic studies revealed that AZT dissipated bacterial proton motive force, which was indispensable for ATP synthesis and flagellar motility. In addition, AZT downregulated bacterial secretion systems involving general and type IV secretion systems (T4SS). Furthermore, the thymidine kinase, which is associated with DNA synthesis, turned out to be the potential target of AZT. Collectively, our work demonstrates the broad inhibitory effect of AZT in preventing ARGs transmission, opening new horizons for controlling AMR.

Pannonibacter anstelovis sp. nov. Isolated from Two Cases of Bloodstream Infections in Paediatric Patients

This study describes two cases of bacteraemia sustained by a new putative Pannonibacter species isolated at the U.O.C. of Microbiology and Virology of the Policlinico of Bari (Bari, Italy) from the blood cultures of two patients admitted to the Paediatric Oncohaematology Unit. Pannonibacter spp. is an environmental Gram-negative bacterium not commonly associated with nosocomial infections. Species identification was performed using Sanger sequencing of the 16S rRNA gene and Whole-Genome Sequencing (WGS) for both strains. Genomic analyses for the two isolates, BLAST similarity search, and phylogeny for the 16S rDNA sequences lead to an assignment to the species Pannonibacter phragmitetus. However, by performing ANIb, ANIm, tetranucleotide correlation, and DNA-DNA digital hybridization, analyses of the two draft genomes showed that they were very different from those of the species P. phragmitetus. MALDI-TOF analysis, assessment of antimicrobial susceptibility by E-test method, and Analytical Profile Index (API) tests were also performed. This result highlights how environmental bacterial species can easily adapt to the human host and, especially in nosocomial environments, also gain pathogenic potential through antimicrobial resistance.

Does Environmental Exposure to Pharmaceutical and Personal Care Product Residues Result in the Selection of Antimicrobial-Resistant Microorganisms, and is this Important in Terms of Human Health Outcomes?

The environment plays a critical role in the development, dissemination, and transmission of antimicrobial resistance (AMR). Pharmaceuticals and personal care products (PPCPs) enter the environment through direct application to the environment and through anthropogenic pollution. Although there is a growing body of evidence defining minimal selective concentrations (MSCs) of antibiotics and the role antibiotics play in horizontal gene transfer (HGT), there is limited evidence on the role of non-antibiotic PPCPs. Existing data show associations with the development of resistance or effects on bacterial growth rather than calculating selective endpoints. Research has focused on laboratory-based systems rather than in situ experiments, although PPCP concentrations found throughout wastewater, natural water, and soil environments are often within the range of laboratory-derived MSCs and at concentrations shown to promote HGT. Increased selection and HGT of AMR by PPCPs will result in an increase in total AMR abundance in the environment, increasing the risk of exposure and potential transmission of environmental AMR to humans. There is some evidence to suggest that humans can acquire resistance from environmental settings, with water environments being the most frequently studied. However, because this is currently limited, we recommend that more evidence be gathered to understand the risk the environment plays in regard to human health. In addition, we recommend that future research efforts focus on MSC-based experiments for non-antibiotic PPCPS, particularly in situ, and investigate the effect of PPCP mixtures on AMR. Environ Toxicol Chem 2024;43:623-636. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Combating antimicrobial resistance: the silent war

Once hailed as miraculous solutions, antibiotics no longer hold that status. The excessive use of antibiotics across human healthcare, agriculture, and animal husbandry has given rise to a broad array of multidrug-resistant (MDR) pathogens, posing formidable treatment challenges. Antimicrobial resistance (AMR) has evolved into a pressing global health crisis, linked to elevated mortality rates in the modern medical era. Additionally, the absence of effective antibiotics introduces substantial risks to medical and surgical procedures. The dwindling interest of pharmaceutical industries in developing new antibiotics against MDR pathogens has aggravated the scarcity issue, resulting in an exceedingly limited pipeline of new antibiotics. Given these circumstances, the imperative to devise novel strategies to combat perilous MDR pathogens has become paramount. Contemporary research has unveiled several promising avenues for addressing this challenge. The article provides a comprehensive overview of these innovative therapeutic approaches, highlighting their mechanisms of action, benefits, and drawbacks.

Urban wastewater disinfection by iron chelates mediated solar photo-Fenton: Effects on seven pathogens and antibiotic resistance transfer potential

The effects of solar photo-Fenton (SPF) process mediated by the iron chelate Fe3+ imminodisuccinic acid (Fe:IDS) on both the inactivation of seven relevant pathogens and the potential for antibiotic resistance transfer (degradation of antibiotic resistance genes (ARGs) and after treatment regrowth), in real secondary treated urban wastewater, were investigated for the first time. A comparison with results obtained by sunlight/H2O2 process and Fe3+ ethylenediaminedisuccinic acid (Fe:EDDS) SPF was also carried out. ARGs were quantified by polymerase chain reaction (PCR) in samples before and after (3 h) the treatment. The persistence of the selected pathogens and ARGs was also evaluated in regrowth tests (72 h) under environmentally mimicking conditions. Fe:IDS SPF resulted to be more effective (from 1.4 log removal for Staphylococcus spp. to 4.3 log removal for Escherichia coli) than Fe:EDDS SPF (from 0.8 log removal for Pseudomonas aeruginosa to 2.0 log removal for Total coliphages) and sunlight/H2O2 (from 1.2 log removal for Clostridium perfringens to 3.3 log removal for E. coli) processes for the seven pathogens investigated. Potential pathogens regrowth was also severely affected, as no substantial regrowth was observed, both in presence and absence of catalase. A similar trend was observed for ARGs removal too (until 0.001 fold change expression for qnrS after 3 h). However, a poor effect and a slight increase in fold change was observed after treatment especially for gyrA, mefA and intl1. Overall, the effect of the investigated processes on ARGs was found to be ARG dependent. Noteworthy, coliphages can regrow after sunlight/H2O2 treatment unlike SPF processes, increasing the risk of antibiotic resistance transfer by transduction mechanism. In conclusion, Fe:IDS SPF is an attractive solution for tertiary treatment of urban wastewater in small wastewater treatment plants as it can provide effective disinfection and a higher protection against antibiotic resistance transfer than the other investigated processes.

Combating Aminoglycoside Resistance: From Structural and Functional Characterisation to Therapeutic Challenges with RKAAT

A comprehensive knowledge of aminoglycoside-modifying enzymes (AMEs) and their role in bacterial resistance mechanisms is urgently required due to the rising incidence of antibiotic resistance, particularly in Klebsiella pneumoniae infections. This study explores the essential features of AMEs, including their structural and functional properties, the processes by which they contribute to antibiotic resistance, and the therapeutic importance of aminoglycosides. The study primarily examines the Recombinant Klebsiella pneumoniae Aminoglycoside Adenylyl Transferase (RKAAT), particularly emphasizing its biophysical characteristics and the sorts of resistance it imparts. Furthermore, this study examines the challenges presented by RKAAT-mediated resistance, an evaluation of treatment methods and constraints, and options for controlling infection. The analysis provides a prospective outlook on strategies to address and reduce antibiotic resistance. This extensive investigation seeks to provide vital insights into the continuing fight against bacterial resistance, directing future research efforts and medicinal approaches.

Natural transformation and cell division delay in competent Staphylococcus aureus

IMPORTANCE

Natural transformation, considered one of the three main mechanisms leading to horizontal gene transfer in bacteria, is able to promote genomic plasticity and foster antibiotic resistance spreading. Conserved machinery and actors required to perform natural transformation have been shown to accumulate at different cellular localizations depending on the model organism considered. Here, we show in the human pathogen Staphylococcus aureus that DNA binding, uptake, and recombination are spatially and temporally coordinated to ensure S. aureus natural transformation. We also reveal that localization of natural transformation proteins occurs in the vicinity of the division septum allowing S. aureus competent cells to block cell division to ensure the success of natural transformation before the final constriction of the cytokinetic ring.

Occurrence, fate and potential health risks of antibiotic resistomes in a constructed wetlands-reservoir ecosystem for drinking water source improvement

The development of effective and feasible engineering technologies to control the transmission of antibiotic resistance genes (ARGs) and pathogenic antibiotic-resistant bacteria (PARB) form drinking water sources is urgently needed for ensuring drinking water safety. In this study, metagenomic analysis was applied to systematically explore the full profiles, removal, and potential health risks of antibiotic resistomes in a large constructed wetlands-reservoir ecosystem (CWs-R) for drinking water source improvement. A total of 343 ARG subtypes belonging to 18 ARG types were identified from water and sediment samples in the CWs-R ecosystem, with an average abundance of 0.339 copies/cell, and bacitracin and multidrug resistance genes were the predominant ARG types in the water and sediment, respectively. The CWs-R ecosystem showed an excellent removal efficiency of ARGs and mobile genetic elements (MGEs) in water, with the total removal rate reaching 64.82 % and 77.09 %, respectively, among which the emergent plant zone and ecological storage unit played major roles. The metagenomic assembly tracked many mobile ARGs and opportunistic pathogens in the CWs-R ecosystem and identified 19 contigs as ARG-carrying pathogens, including Staphylococcus aureus, Salmonella enterica, Escherichia coli, and Klebsiella pneumonia. Overall, the CWs-R ecosystem has an important role in reducing the potential public health risks posed by antibiotic resistomes in drinking water sources but still cannot fully eliminate them. Therefore, we further classified water and sediment samples in the CWs-R ecosystem and identified potential ARGs and PARB indicators based on the metagenomic analysis results by considering the potential for horizontal transfer of ARGs to opportunistic pathogens. Taken together, this work demonstrates the CWs-R ecosystem as an economical and feasible engineering technology to reduce the dissemination of antibiotic resistomes in the drinking water source, provides useful information for monitoring and controlling antibiotic resistance in similar water sources, and ensures biosafety of drinking water.

Comprehensive insights into antibiotic resistance gene migration in microalgal-bacterial consortia: Mechanisms, factors, and perspectives

With the overuse of antibiotics, antibiotic resistance gene (ARG) prevalence is gradually increasing. ARGs are considered emerging contaminants that are broadly concentrated and dispersed in most aquatic environments. Recently, interest in microalgal-bacterial biotreatment of antibiotics has increased, as eukaryotes are not the primary target of antimicrobial drugs. Moreover, research has shown that microalgal-bacterial consortia can minimize the transmission of antibiotic resistance in the environment. Unfortunately, reviews surrounding the ARG migration mechanism in microalgal-bacterial consortia have not yet been performed. This review briefly introduces the migration of ARGs in aquatic environments. Additionally, an in-depth summary of horizontal gene transfer (HGT) between cyanobacteria and bacteria and from bacteria to eukaryotic microalgae is presented. Factors influencing gene transfer in microalgal-bacterial consortia are discussed systematically, including bacteriophage abundance, environmental conditions (temperature, pH, and nutrient availability), and other selective pressure conditions including nanomaterials, heavy metals, and pharmaceuticals and personal care products. Furthermore, considering that quorum sensing could be involved in DNA transformation by affecting secondary metabolites, current knowledge surrounding quorum sensing regulation of HGT of ARGs is summarized. In summary, this review gives valuable information to promote the development of practical and innovative techniques for ARG removal by microalgal-bacterial consortia.

Visualizing dynamic competence pili and DNA capture throughout the long axis of Bacillus subtilis

The first step in the process of bacterial natural transformation is DNA capture. Although long hypothesized based on genetics and functional experiments, the pilus structure responsible for initial DNA binding had not yet been visualized for Bacillus subtilis. Here, we visualize functional competence pili in Bacillus subtilis using fluorophore-conjugated maleimide labeling in conjunction with epifluorescence microscopy. In strains that produce pilin monomers within tenfold of wild-type levels, the median length of detectable pili is 300 nm. These pili are retractile and associate with DNA. The analysis of pilus distribution at the cell surface reveals that they are predominantly located along the long axis of the cell. The distribution is consistent with localization of proteins associated with subsequent transformation steps, DNA binding, and DNA translocation in the cytosol. These data suggest a distributed model for B. subtilis transformation machinery, in which initial steps of DNA capture occur throughout the long axis of the cell and subsequent steps may also occur away from the cell poles. IMPORTANCE This work provides novel visual evidence for DNA translocation across the cell wall during Bacillus subtilis natural competence, an essential step in the natural transformation process. Our data demonstrate the existence of natural competence-associated retractile pili that can bind exogenous DNA. Furthermore, we show that pilus biogenesis occurs throughout the cell long axis. These data strongly support DNA translocation occurring all along the lateral cell wall during natural competence, wherein pili are produced, bind to free DNA in the extracellular space, and finally retract to pull the bound DNA through the gap in the cell wall created during pilus biogenesis.

Restriction-methylation systems regulate transformation in Acinetobacter baumannii

Antimicrobial resistance in Acinetobacter baumannii is a major concern. Natural transformation remains understudied as a horizontal gene transfer (HGT) mechanism for the spread of resistance genes. Recent work (Vesel et al.) reveals a profound impact of the state of donor DNA methylation with strong implications for HGT of resistance determinants in this worrisome pathogen.

Nematodes Degrade Extracellular Antibiotic Resistance Genes by Secreting DNase II Encoded by the nuc-1 Gene

This study investigated the degradation performance and mechanism of extracellular antibiotic resistance genes (eARGs) by nematodes using batch degradation experiments, mutant strain validation, and phylogenetic tree construction. Caenorhabditis elegans, a representative nematode, effectively degraded approximately 99.999% of eARGs (tetM and kan) in 84 h and completely deactivated them within a few hours. Deoxyribonuclease (DNase) II encoded by nuc-1 in the excretory and secretory products of nematodes was the primary mechanism. A neighbor-joining phylogenetic tree indicated the widespread presence of homologs of the NUC-1 protein in other nematodes, such as Caenorhabditis remanei and Caenorhabditis brenneri, whose capabilities of degrading eARGs were then experimentally confirmed. C. elegans remained effective in degrading eARGs under the effects of natural organic matter (5, 10, and 20 mg/L, 5.26-6.22 log degradation), cation (2.0 mM Mg2+ and 2.5 mM Ca2+, 5.02-5.04 log degradation), temperature conditions (1, 20, and 30 °C, 1.21-5.26 log degradation), and in surface water and wastewater samples (4.78 and 3.23 log degradation, respectively). These findings highlight the pervasive but neglected role of nematodes in the natural decay of eARGs and provide novel approaches for antimicrobial resistance mitigation biotechnology by introducing nematodes to wastewater, sludge, and biosolids.

Testing for the fitness benefits of natural transformation during community-embedded evolution

Natural transformation is a process where bacteria actively take up DNA from the environment and recombine it into their genome or reconvert it into extra-chromosomal genetic elements. The evolutionary benefits of transformation are still under debate. One main explanation is that foreign allele and gene uptake facilitates natural selection by increasing genetic variation, analogous to meiotic sex. However, previous experimental evolution studies comparing fitness gains of evolved transforming- and isogenic non-transforming strains have yielded mixed support for the 'sex hypothesis.' Previous studies testing the sex hypothesis for natural transformation have largely ignored species interactions, which theory predicts provide conditions favourable to sex. To test for the adaptive benefits of bacterial transformation, the naturally transformable wild-type Acinetobacter baylyi and a transformation-deficient ∆comA mutant were evolved for 5 weeks. To provide strong and potentially fluctuating selection, A. baylyi was embedded in a community of five other bacterial species. DNA from a pool of different Acinetobacter strains was provided as a substrate for transformation. No effect of transformation ability on the fitness of evolved populations was found, with fitness increasing non-significantly in most treatments. Populations showed fitness improvement in their respective environments, with no apparent costs of adaptation to competing species. Despite the absence of fitness effects of transformation, wild-type populations evolved variable transformation frequencies that were slightly greater than their ancestor which potentially could be caused by genetic drift.

Combined bisdemethoxycurcumin and potassium iodide-mediated antimicrobial photodynamic therapy

Antimicrobial photodynamic therapy is emerging as a promising way to treat infections with minimal side effects. Typically, a single photosensitizer used in photodynamic therapy is capable of generating only one type of reactive oxygen species, which may have inadequate capability to eradicate certain types of microbes, especially Candida species. Thus, the use of combined photosensitizers is examined as a means of achieving superior antimicrobial results. We postulate that bisdemethoxycurcumin, a type I reactive oxygen species generator, combined with potassium iodide, an antimicrobial iodide molecule, might exhibit superior antimicrobial effects compared to a single photosensitizer-mediated photodynamic therapy. The effects of bisdemethoxycurcumin + potassium iodide + dental blue light on Candida albicans reduction were examined. Candida biofilms were treated with 20, 40 or 80 μM bisdemethoxycurcumin, 100 mM potassium iodide or a combination of these species for 20 min before irradiation with a dental blue light (90 J/cm²). The negative and positive controls were phosphate buffer saline and nystatin at 1 : 100,000 units/ml, respectively. Candidal numbers were quantified at 0, 1, 6 and 24 h. Hydroxyl radicals were spectrophotometrically measured using 2-[6-(4'amino phynoxyl-3H-xanthen-3-on-9-yl)] benzoic acid or APF probe-mediated fluorescence intensity (Varioskan) at 490/515 nm (excitation/emission). Candidal counts and hydroxyl radical comparisons were performed using the Kruskal-Wallis test and one-way ANOVA, respectively. Correlations between candidal numbers and hydroxyl radical levels were done with a Pearson correlation test. Forty μM bisdemethoxycurcumin+100 mM KI could provide a 3.5 log₁₀ CFU/ml reduction after 6 h. Bisdemethoxycurcumin alone generated OH levels that were strongly correlated with candidal reduction. In conclusion, 40 μM bisdemethoxycurcumin+100 mM KI could reduce C. albicans biofilm.

The ComRS-SigX Pathway Regulates Natural Transformation in Streptococcus ferus

The ability to take up and incorporate foreign DNA via natural transformation is a well-known characteristic of some species of Streptococcus, and is a mechanism that rapidly allows for the acquisition of antibacterial resistance. Here, we describe that the understudied species Streptococcus ferus is also capable of natural transformation and uses a system analogous to that identified in Streptococcus mutans. S. mutans natural transformation is under the control of the alternative sigma factor sigX (also known as comX), whose expression is induced by two types of peptide signals: CSP (competence stimulating peptide, encoded by comC) and XIP (sigX-inducing peptide, encoded by comS). These systems induce competence via either the two-component signal-transduction system ComDE or the RRNPP transcriptional regulator ComR, respectively. Protein and nucleotide homology searches identified putative orthologs of comRS and sigX in S. ferus, but not homologs of S. mutans blpRH (also known as comDE). We demonstrate that natural transformation in S. ferus is induced by a small, double-tryptophan containing sigX-inducing peptide (XIP), akin to that of S. mutans, and requires the presence of the comR and sigX orthologs for efficient transformation. Additionally, we find that natural transformation is induced in S. ferus by both the native XIP and the XIP variant of S. mutans, implying that cross talk between the two species is possible. This process has been harnessed to construct gene deletions in S. ferus and provides a method to genetically manipulate this understudied species. IMPORTANCE Natural transformation is the process by which bacteria take up DNA and allows for acquisition of new genetic traits, including those involved in antibiotic resistance. This study demonstrates that the understudied species Streptococcus ferus is capable of natural transformation using a peptide-pheromone system like that previously identified in Streptococcus mutans and provides a framework for future studies concerning this organism.

Environmental concentrations of surfactants as a trigger for climax of horizonal gene transfer of antibiotic resistance

Ubiquitous antibiotic resistance genes (ARGs) is a significant global human health concern. Surfactants have been extensively used worldwide, and the consumption of surfactants containing hygiene, cleaning agents and disinfectants was multiplied during COVID-19 pandemic, which have caused significantly increased pollution of surfactants in aquatic environment. Whether such ever-increasing surfactant concentration boost dissemination risk of ARGs still remains unknown. Here the effects of three typical surfactants such as sodium dodecyl sulfate, cetyltrimethylammonium bromide and benzalkonium chloride on the transformation of pUC19 plasmid (2686 bp)-borne ARGs to recipient bacteria E. coli DH5ɑ were investigated. It was found that these surfactants at environmental concentrations facilitated horizonal gene transfer (HGT) via transformation. The transformation triggering concentrations for the three surfactants were 0.25-0.34 mg/L with a maximum increased transformation frequency of 13.51-22.93-fold. The mechanisms involved in activated HGT of ARGs via transformation triggered by surfactants could be mainly attributed to the increased production of reactive oxygen species, which further enhanced cell membrane permeability. These findings provide new sights for understanding of ARG propagation and also imply that the drastic rise of surfactant concentration in aquatic environment may significantly increase the dissemination risk of antibiotic resistance.

Visualizing dynamic competence pili and DNA capture throughout the long axis of Bacillus subtilis

The first step in the process of bacterial natural transformation is DNA capture. Although long-hypothesized based on genetics and functional experiments, the pilus structure responsible for initial DNA-binding had not yet been visualized for Bacillus subtilis. Here, we visualize functional competence pili in Bacillus subtilis using fluorophore-conjugated maleimide labeling in conjunction with epifluorescence microscopy. In strains that produce pilin monomers within ten-fold of wild type levels, the median length of detectable pili is 300nm. These pili are retractile and associate with DNA. Analysis of pilus distribution at the cell surface reveals that they are predominantly located along the long axis of the cell. The distribution is consistent with localization of proteins associated with subsequent transformation steps, DNA-binding and DNA translocation in the cytosol. These data suggest a distributed model for B. subtilis transformation machinery, in which initial steps of DNA capture occur throughout the long axis of the cell and subsequent steps may also occur away from the cell poles.

Catch me if you can: capturing microbial community transformation by extracellular DNA using Hi-C sequencing

The transformation of environmental microorganisms by extracellular DNA is an overlooked mechanism of horizontal gene transfer and evolution. It initiates the acquisition of exogenous genes and propagates antimicrobial resistance alongside vertical and conjugative transfers. We combined mixed-culture biotechnology and Hi-C sequencing to elucidate the transformation of wastewater microorganisms with a synthetic plasmid encoding GFP and kanamycin resistance genes, in the mixed culture of chemostats exposed to kanamycin at concentrations representing wastewater, gut and polluted environments (0.01-2.5-50-100 mg L^-1). We found that the phylogenetically distant Gram-negative Runella (102 Hi-C links), Bosea (35), Gemmobacter (33) and Zoogloea (24) spp., and Gram-positive Microbacterium sp. (90) were transformed by the foreign plasmid, under high antibiotic exposure (50 mg L^-1). In addition, the antibiotic pressure shifted the origin of aminoglycoside resistance genes from genomic DNA to mobile genetic elements on plasmids accumulating in microorganisms. These results reveal the power of Hi-C sequencing to catch and surveil the transfer of xenogenetic elements inside microbiomes.

Evaluation of Efflux-Mediated Resistance and Biofilm formation in Virulent Pseudomonas aeruginosa Associated with Healthcare Infections

Pseudomonas aeruginosa is a significant pathogen identified with healthcare-associated infections. The present study evaluates the role of biofilm and efflux pump activities in influencing high-level resistance in virulent P. aeruginosa strains in clinical infection. Phenotypic resistance in biotyped Pseudomonas aeruginosa (n = 147) from diagnosed disease conditions was classified based on multiple antibiotic resistance (MAR) indices and analysed with logistic regression for risk factors. Efflux pump activity, biofilm formation, and virulence factors were analysed for optimal association in Pseudomonas infection using receiver operation characteristics (ROC). Age-specificity (OR [CI] = 0.986 [0.946-1.027]), gender (OR [CI] = 1.44 [0.211-9.827]) and infection sources (OR [CI] = 0.860 [0.438-1.688]) were risk variables for multidrug resistance (MDR)-P. aeruginosa infection (p < 0.05). Biofilm formers caused 48.2% and 18.5% otorrhea and wound infections (95% CI = 0.820-1.032; p = 0.001) respectively and more than 30% multidrug resistance (MDR) strains demonstrated high-level efflux pump activity (95% CI = 0.762-1.016; p = 0.001), protease (95% CI = 0.112-0.480; p = 0.003), lipase (95% CI = 0.143-0.523; p = 0.001), and hemolysin (95% CI = 1.109-1.780; p = 0.001). Resistance relatedness of more than 80% and 60% to cell wall biosynthesis inhibitors (ceftazidime, ceffproxil, augumentin, ampicillin) and, DNA translational and transcriptional inhibitors (gentamicin, ciprofloxacin, ofloxacin, nitrofurantoin) were observed (p < 0.05). Strong efflux correlation (r = 0.85, p = 0.034) with MDR strains, with high predictive performances in efflux pump activity (ROC-AUC 0.78), biofilm formation (ROC-AUC 0.520), and virulence hierarchical-clustering. Combine activities of the expressed efflux pump and biofilm formation in MDR-P. aeruginosa pose risk to clinical management and infection control.

The ComRS-SigX pathway regulates natural transformation in Streptococcus ferus

The ability to take up and incorporate foreign DNA via natural transformation is a well-known characteristic of some species of Streptococcus, and is a mechanism that rapidly allows for the acquisition of antibacterial resistance. Here, we describe that the understudied species Streptococcus ferus is also capable of natural transformation and uses a system analogous to that identified in Streptococcus mutans . S. mutans natural transformation is under the control of the alternative sigma factor sigX (also known as comX ), whose expression is induced by two types of peptide signals: CSP ( c ompetence s timulating p eptide, encoded by comC ) and XIP ( sig X -inducing p eptide, encoded by comS ). These systems induce competence via either the two-component signal-transduction system ComDE or the RRNPP transcriptional regulator ComR, respectively. Protein and nucleotide homology searches identified putative orthologs of comRS and sigX in S. ferus , but not homologs of S. mutans blpRH (also known as comDE ). We demonstrate that natural transformation in S. ferus is induced by a small, double-tryptophan containing competence-inducing peptide (XIP), akin to that of S. mutans , and requires the presence of the comR and sigX orthologs for efficient transformation. Additionally, we find that natural transformation is induced in S. ferus by both the native XIP and the XIP variant of S. mutans , implying that crosstalk between the two species is possible. This process has been harnessed to construct gene deletions in S. ferus and provides a method to genetically manipulate this understudied species.

IMPORTANCE

Natural transformation is the process by which bacteria take up DNA and allows for acquisition of new genetic traits, including those involved in antibiotic resistance. This study demonstrates that the understudied species Streptococcus ferus is capable of natural transformation using a peptide-pheromone system like that previously identified in Streptococcus mutans and provides a framework for future studies concerning this organism.

Dominance of phage particles carrying antibiotic resistance genes in the viromes of retail food sources

The growth of antibiotic resistance has stimulated interest in understanding the mechanisms by which antibiotic resistance genes (ARG) are mobilized. Among them, studies analyzing the presence of ARGs in the viral fraction of environmental, food and human samples, and reporting bacteriophages as vehicles of ARG transmission, have been the focus of increasing research. However, it has been argued that in these studies the abundance of phages carrying ARGs has been overestimated due to experimental contamination with non-packaged bacterial DNA or other elements such as outer membrane vesicles (OMVs). This study aims to shed light on the extent to which phages, OMVs or contaminating non-packaged DNA contribute as carriers of ARGs in the viromes. The viral fractions of three types of food (chicken, fish, and mussels) were selected as sources of ARG-carrying phage particles, whose ability to infect and propagate in an Escherichia coli host was confirmed after isolation. The ARG-containing fraction was further purified by CsCl density gradient centrifugation and, after removal of DNA outside the capsids, ARGs inside the particles were confirmed. The purified fraction was stained with SYBR Gold, which allowed the visualization of phage capsids attached to and infecting E. coli cells. Phages with Myoviridae and Siphoviridae morphology were observed by electron microscopy. The proteins in the purified fraction belonged predominantly to phages (71.8% in fish, 52.9% in mussels, 78.7% in chicken sample 1, and 64.1% in chicken sample 2), mainly corresponding to tail, capsid, and other structural proteins, whereas membrane proteins, expected to be abundant if OMVs were present, accounted for only 3.8-21.4% of the protein content. The predominance of phage particles in the viromes supports the reliability of the protocols used in this study and in recent findings on the abundance of ARG-carrying phage particles.

Explaining the resistomes in a megacity's water supply catchment: Roles of microbial assembly-dominant taxa, niched environments and pathogenic bacteria

Antibiotic resistance genes (ARGs) in drinking water sources suggest the possible presence of resistant microorganisms that jeopardize human health. However, explanations for the presence of specific ARGs in situ are largely unknown, especially how their prevalence is affected by local microbial ecology, taxa assembly and community-wide gene transfer. Here, we characterized resistomes and bacterial communities in the Taipu River catchment, which feeds a key drinking water reservoir to a global megacity, Shanghai. Overall, ARG abundances decreased significantly as the river flowed downstream towards the reservoir (P < 0.01), whereas the waterborne bacteria assembled deterministically (|βNRI| > 2.0) as a function of temperature and dissolved oxygen conditions with the assembly-dominant taxa (e.g. Ilumatobacteraceae and Cyanobiaceae) defining local resistomes (P < 0.01, Cohen's D = 4.22). Bacterial hosts of intragenomic ARGs stayed at the same level across the catchment (60 ∼ 70 genome copies per million reads). Among them, the putative resistant pathogens (e.g. Burkholderiaceae) carried mixtures of ARGs that exhibited high transmission probability (transfer counts = 126, P < 0.001), especially with the microbial assembly-dominant taxa. These putative resistant pathogens had densities ranging form 3.0 to 4.0 × 10⁶ cell/L, which was more pronouncedly affected by resistome and microbial assembly structures than environmental factors (SEM, std-coeff β = 0.62 vs. 0.12). This work shows that microbial assembly and resistant pathogens play predominant roles in prevelance and dissemination of resistomes in receiving water, which deserves greater attention in devisng control strategies for reducing in-situ ARGs and resistant strains in a catchment.

Emerging issues in probiotic safety: 2023 perspectives

Probiotics are used for both generally healthy consumers and in clinical settings. However, theoretical and proven adverse events from probiotic consumption exist. New probiotic strains and products, as well as expanding use of probiotics into vulnerable populations, warrants concise, and actionable recommendations on how to work toward their safe and effective use. The International Scientific Association for Probiotics and Prebiotics convened a meeting to discuss and produce evidence-based recommendations on potential acute and long-term risks, risks to vulnerable populations, the importance for probiotic product quality to match the needs of vulnerable populations, and the need for adverse event reporting related to probiotic use. The importance of whole genome sequencing, which enables determination of virulence, toxin, and antibiotic resistance genes, as well as clear assignment of species and strain identity, is emphasized. We present recommendations to guide the scientific and medical community on judging probiotic safety.

Deciphering the genetic network and programmed regulation of antimicrobial resistance in bacterial pathogens

Antimicrobial resistance (AMR) in bacteria is an important global health problem affecting humans, animals, and the environment. AMR is considered as one of the major components in the "global one health". Misuse/overuse of antibiotics in any one of the segments can impact the integrity of the others. In the presence of antibiotic selective pressure, bacteria tend to develop several defense mechanisms, which include structural changes of the bacterial outer membrane, enzymatic processes, gene upregulation, mutations, adaptive resistance, and biofilm formation. Several components of mobile genetic elements (MGEs) play an important role in the dissemination of AMR. Each one of these components has a specific function that lasts long, irrespective of any antibiotic pressure. Integrative and conjugative elements (ICEs), insertion sequence elements (ISs), and transposons carry the antimicrobial resistance genes (ARGs) on different genetic backbones. Successful transfer of ARGs depends on the class of plasmids, regulons, ISs proximity, and type of recombination systems. Additionally, phage-bacterial networks play a major role in the transmission of ARGs, especially in bacteria from the environment and foods of animal origin. Several other functional attributes of bacteria also get successfully modified to acquire ARGs. These include efflux pumps, toxin-antitoxin systems, regulatory small RNAs, guanosine pentaphosphate signaling, quorum sensing, two-component system, and clustered regularly interspaced short palindromic repeats (CRISPR) systems. The metabolic and virulence state of bacteria is also associated with a range of genetic and phenotypic resistance mechanisms. In spite of the availability of a considerable information on AMR, the network associations between selection pressures and several of the components mentioned above are poorly understood. Understanding how a pathogen resists and regulates the ARGs in response to antimicrobials can help in controlling the development of resistance. Here, we provide an overview of the importance of genetic network and regulation of AMR in bacterial pathogens.

Effective antibiotic dosing in the presence of resistant strains

Mathematical models can be very useful in determining efficient and successful antibiotic dosing regimens. In this study, we consider the problem of determining optimal antibiotic dosing when bacteria resistant to antibiotics are present in addition to susceptible bacteria. We consider two different models of resistance acquisition, both involve the horizontal transfer (HGT) of resistant genes from a resistant to a susceptible strain. Modeling studies on HGT and study of optimal antibiotic dosing protocols in the literature, have been mostly focused on transfer of resistant genes via conjugation, with few studies on HGT via transformation. We propose a deterministic ODE based model of resistance acquisition via transformation, followed by a model that takes into account resistance acquisition through conjugation. Using a numerical optimization algorithm to determine the 'best' antibiotic dosing strategy. To illustrate our optimization method, we first consider optimal dosing when all the bacteria are susceptible to the antibiotic. We then consider the case where resistant strains are present. We note that constant periodic dosing may not always succeed in eradicating the bacteria while an optimal dosing protocol is successful. We determine the optimal dosing strategy in two different scenarios: one where the total bacterial population is to be minimized, and the next where we want to minimize the bacterial population at the end of the dosing period. We observe that the optimal strategy in the first case involves high initial dosing with dose tapering as time goes on, while in the second case, the optimal dosing strategy is to increase the dosing at the beginning of the dose cycles followed by a possible dose tapering. As a follow up study we intend to look at models where 'persistent' bacteria may be present in additional to resistant and susceptible strain and determine the optimal dosing protocols in this case.

The Spread of Antibiotic Resistance Genes In Vivo Model

Infections caused by antibiotic-resistant bacteria are a major public health threat. The emergence and spread of antibiotic resistance genes (ARGs) in the environment or clinical setting pose a serious threat to human and animal health worldwide. Horizontal gene transfer (HGT) of ARGs is one of the main reasons for the dissemination of antibiotic resistance in vitro and in vivo environments. There is a consensus on the role of mobile genetic elements (MGEs) in the spread of bacterial resistance. Most drug resistance genes are located on plasmids, and the spread of drug resistance genes among microorganisms through plasmid-mediated conjugation transfer is the most common and effective way for the spread of multidrug resistance. Experimental studies of the processes driving the spread of antibiotic resistance have focused on simple in vitro model systems, but the current in vitro protocols might not correctly reflect the HGT of antibiotic resistance genes in realistic conditions. This calls for better models of how resistance genes transfer and disseminate in vivo. The in vivo model can better mimic the situation that occurs in patients, helping study the situation in more detail. This is crucial to develop innovative strategies to curtail the spread of antibiotic resistance genes in the future. This review aims to give an overview of the mechanisms of the spread of antibiotic resistance genes and then demonstrate the spread of antibiotic resistance genes in the in vivo model. Finally, we discuss the challenges in controlling the spread of antibiotic resistance genes and their potential solutions.