# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 3784 | 0 | 1.0000 | Insight into the mobilome of Aeromonas strains. The mobilome is a pool of genes located within mobile genetic elements (MGE), such as plasmids, IS elements, transposons, genomic/pathogenicity islands, and integron-associated gene cassettes. These genes are often referred to as "flexible" and may encode virulence factors, toxic compounds as well as resistance to antibiotics. The phenomenon of MGE transfer between bacteria, known as horizontal gene transfer (HGT), is well documented. The genes present on MGE are subject to continuous processes of evolution and environmental changes, largely induced or significantly accelerated by man. For bacteria, the only chance of survival in an environment contaminated with toxic chemicals, heavy metals and antibiotics is the acquisition of genes providing the ability to survive in such conditions. The process of acquiring and spreading antibiotic resistance genes (ARG) is of particular significance, as it is important for the health of humans and animals. Therefore, it is important to thoroughly study the mobilome of Aeromonas spp. that is widely distributed in various environments, causing many diseases in fishes and humans. This review discusses the recently published information on MGE prevalent in Aeromonas spp. with special emphasis on plasmids belonging to different incompatibility groups, i.e., IncA/C, IncU, IncQ, IncF, IncI, and ColE-type. The vast majority of plasmids carry a number of different transposons (Tn3, Tn21, Tn1213, Tn1721, Tn4401), the 1st, 2nd, or 3rd class of integrons, IS elements (e.g., IS26, ISPa12, ISPa13, ISKpn8, ISKpn6) and encode determinants such as antibiotic and mercury resistance genes, as well as virulence factors. Although the actual role of Aeromonas spp. as a human pathogen remains controversial, species of this genus may pose a serious risk to human health. This is due to the considerable potential of their mobilome, particularly in terms of antibiotic resistance and the possibility of the horizontal transfer of resistance genes. | 2015 | 26074893 |
| 9650 | 1 | 0.9998 | Plasmid-Encoded Traits Vary across Environments. Plasmids are key mobile genetic elements in bacterial evolution and ecology as they allow the rapid adaptation of bacteria under selective environmental changes. However, the genetic information associated with plasmids is usually considered separately from information about their environmental origin. To broadly understand what kinds of traits may become mobilized by plasmids in different environments, we analyzed the properties and accessory traits of 9,725 unique plasmid sequences from a publicly available database with known bacterial hosts and isolation sources. Although most plasmid research focuses on resistance traits, such genes made up <1% of the total genetic information carried by plasmids. Similar to traits encoded on the bacterial chromosome, plasmid accessory trait compositions (including general Clusters of Orthologous Genes [COG] functions, resistance genes, and carbon and nitrogen genes) varied across seven broadly defined environment types (human, animal, wastewater, plant, soil, marine, and freshwater). Despite their potential for horizontal gene transfer, plasmid traits strongly varied with their host's taxonomic assignment. However, the trait differences across environments of broad COG categories could not be entirely explained by plasmid host taxonomy, suggesting that environmental selection acts on the plasmid traits themselves. Finally, some plasmid traits and environments (e.g., resistance genes in human-related environments) were more often associated with mobilizable plasmids (those having at least one detected relaxase) than others. Overall, these findings underscore the high level of diversity of traits encoded by plasmids and provide a baseline to investigate the potential of plasmids to serve as reservoirs of adaptive traits for microbial communities. IMPORTANCE Plasmids are well known for their role in the transmission of antibiotic resistance-conferring genes. Beyond human and clinical settings, however, they disseminate many other types of genes, including those that contribute to microbially driven ecosystem processes. In this study, we identified the distribution of traits genetically encoded by plasmids isolated from seven broadly categorized environments. We find that plasmid trait content varied with both bacterial host taxonomy and environment and that, on average, half of the plasmids were potentially mobilizable. As anthropogenic activities impact ecosystems and the climate, investigating and identifying the mechanisms of how microbial communities can adapt will be imperative for predicting the impacts on ecosystem functioning. | 2023 | 36629415 |
| 3909 | 2 | 0.9998 | Biosolids as a Source of Antibiotic Resistance Plasmids for Commensal and Pathogenic Bacteria. Antibiotic resistance (AR) is a threat to modern medicine, and plasmids are driving the global spread of AR by horizontal gene transfer across microbiomes and environments. Determining the mobile resistome responsible for this spread of AR among environments is essential in our efforts to attenuate the current crisis. Biosolids are a wastewater treatment plant (WWTP) byproduct used globally as fertilizer in agriculture. Here, we investigated the mobile resistome of biosolids that are used as fertilizer. This was done by capturing resistance plasmids that can transfer to human pathogens and commensal bacteria. We used a higher-throughput version of the exogenous plasmid isolation approach by mixing several ESKAPE pathogens and a commensal Escherichia coli with biosolids and screening for newly acquired resistance to about 10 antibiotics in these strains. Six unique resistance plasmids transferred to Salmonella typhimurium, Klebsiella aerogenes, and E. coli. All the plasmids were self-transferable and carried 3-6 antibiotic resistance genes (ARG) conferring resistance to 2-4 antibiotic classes. These plasmids-borne resistance genes were further embedded in genetic elements promoting intracellular recombination (i.e., transposons or class 1 integrons). The plasmids belonged to the broad-host-range plasmid (BHR) groups IncP-1 or PromA. Several of them were persistent in their new hosts when grown in the absence of antibiotics, suggesting that the newly acquired drug resistance traits would be sustained over time. This study highlights the role of BHRs in the spread of ARG between environmental bacteria and human pathogens and commensals, where they may persist. The work further emphasizes biosolids as potential vehicles of highly mobile plasmid-borne antibiotic resistance genes. | 2021 | 33967971 |
| 4161 | 3 | 0.9998 | Integron and its role in antimicrobial resistance: A literature review on some bacterial pathogens. In recent years, different acquired resistance mechanisms, including transposons, bacteriophages, plasmids, and integrons have been identified as involved in the spread of resistance genes in bacteria. The role of integrons as mobile genetic elements playing a central role in antibiotic resistance has been well studied and documented. Integrons are the ancient structures that mediate the evolution of bacteria by acquiring, storing, disposing, and resorting to the reading frameworks in gene cassettes. The term integron describes a large family of genetic elements, all of which are able to capture gene cassettes. Integrons were classified into three important classes based on integrase intI gene sequence. Integrons can carry and spread the antibiotic resistance genes among bacteria and are among the most significant routes of distribution of resistance genes via horizontal transfer. All integrons have three essential core features. The first feature is intI, the second one is an integron-associated recombination site, attI, and an integron-associated promoter, Pc, is the last feature. Among them, the class 1 integron is a major player in the dissemination of antibiotic resistance genes across pathogens and commensals. Various classes of integrons possessing a wide variety of gene cassettes are distributed in bacteria throughout the world. This review thus focuses on the distribution of integrons among important bacteria. | 2021 | 33953851 |
| 3775 | 4 | 0.9998 | Mobile Genetic Elements Drive Antimicrobial Resistance Gene Spread in Pasteurellaceae Species. Mobile genetic elements (MGEs) and antimicrobial resistance (AMR) drive important ecological relationships in microbial communities and pathogen-host interaction. In this study, we investigated the resistome-associated mobilome in 345 publicly available Pasteurellaceae genomes, a large family of Gram-negative bacteria including major human and animal pathogens. We generated a comprehensive dataset of the mobilome integrated into genomes, including 10,820 insertion sequences, 2,939 prophages, and 43 integrative and conjugative elements. Also, we assessed plasmid sequences of Pasteurellaceae. Our findings greatly expand the diversity of MGEs for the family, including a description of novel elements. We discovered that MGEs are comparable and dispersed across species and that they also co-occur in genomes, contributing to the family's ecology via gene transfer. In addition, we investigated the impact of these elements in the dissemination and shaping of AMR genes. A total of 55 different AMR genes were mapped to 721 locations in the dataset. MGEs are linked with 77.6% of AMR genes discovered, indicating their important involvement in the acquisition and transmission of such genes. This study provides an uncharted view of the Pasteurellaceae by demonstrating the global distribution of resistance genes linked with MGEs. | 2021 | 35069478 |
| 4560 | 5 | 0.9998 | High-resolution genomic surveillance elucidates a multilayered hierarchical transfer of resistance between WWTP- and human/animal-associated bacteria. BACKGROUND: Our interconnected world and the ability of bacteria to quickly swap antibiotic resistance genes (ARGs) make it particularly important to establish the epidemiological links of multidrug resistance (MDR) transfer between wastewater treatment plant (WWTP)- and human/animal-associated bacteria, under the One Health framework. However, evidence of ARGs exchange and potential factors that contribute to this transfer remain limited. RESULTS: Here, by combining culture-based population genomics and genetic comparisons with publicly available datasets, we reconstructed the complete genomes of 82 multidrug-resistant isolates from WWTPs and found that most WWTP-associated isolates were genetically distinct from their closest human/animal-associated relatives currently available in the public database. Even in the minority of lineages that were closely related, WWTP-associated isolates were characterized by quite different plasmid compositions. We identified a high diversity of circular plasmids (264 in total, of which 141 were potentially novel), which served as the main source of resistance, and showed potential horizontal transfer of ARG-bearing plasmids between WWTP- and humans/animal-associated bacteria. Notably, the potentially transferred ARGs and virulence factors (VFs) with different genetic backgrounds were closely associated with flanking insertion sequences (ISs), suggesting the importance of synergy between plasmids and ISs in mediating a multilayered hierarchical transfer of MDR and potentiating the emergence of MDR-hypervirulent clones. CONCLUSION: Our findings advance the current efforts to establish potential epidemiological links of MDR transmission between WWTP- and human/animal-associated bacteria. Plasmids play an important role in mediating the transfer of ARGs and the IS-associated ARGs that are carried by conjugative plasmids should be prioritized to tackle the spread of resistance. Video Abstract. | 2022 | 35078531 |
| 4162 | 6 | 0.9998 | Gene sharing among plasmids and chromosomes reveals barriers for antibiotic resistance gene transfer. The emergence of antibiotic resistant bacteria is a major threat to modern medicine. Rapid adaptation to antibiotics is often mediated by the acquisition of plasmids carrying antibiotic resistance (ABR) genes. Nonetheless, the determinants of plasmid-mediated ABR gene transfer remain debated. Here, we show that the propensity of ABR gene transfer via plasmids is higher for accessory chromosomal ABR genes in comparison with core chromosomal ABR genes, regardless of the resistance mechanism. Analysing the pattern of ABR gene occurrence in the genomes of 2635 Enterobacteriaceae isolates, we find that 33% of the 416 ABR genes are shared between chromosomes and plasmids. Phylogenetic reconstruction of ABR genes occurring on both plasmids and chromosomes supports their evolution by lateral gene transfer. Furthermore, accessory ABR genes (encoded in less than 10% of the chromosomes) occur more abundantly in plasmids in comparison with core ABR genes (encoded in greater than or equal to 90% of the chromosomes). The pattern of ABR gene occurrence in plasmids and chromosomes is similar to that in the total Escherichia genome. Our results thus indicate that the previously recognized barriers for gene acquisition by lateral gene transfer apply also to ABR genes. We propose that the functional complexity of the underlying ABR mechanism is an important determinant of ABR gene transferability. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'. | 2022 | 34839702 |
| 4160 | 7 | 0.9998 | The association between the genetic structures of commonly incompatible plasmids in Gram-negative bacteria, their distribution and the resistance genes. Incompatible plasmids play a crucial role in the horizontal transfer of antibiotic resistance in bacteria, particularly in Gram-negative bacteria, and have thus attracted considerable attention in the field of microbiological research. In the 1970s, these plasmids, housing an array of resistance genes and genetic elements, were predominantly discovered. They exhibit a broad presence in diverse host bacteria, showcasing diversity in geographic distribution and the spectrum of antibiotic resistance genes. The complex genetic structure of plasmids further accelerates the accumulation of resistance genes in Gram-negative bacteria. This article offers a comprehensive review encompassing the discovery process, host distribution, geographic prevalence, carried resistance genes, and the genetic structure of different types incompatible plasmids, including IncA, IncC, IncF, IncL, IncM, IncH, and IncP. It serves as a valuable reference for enhancing our understanding of the role of these different types of plasmids in bacterial evolution and the dissemination of antibiotic resistance. | 2024 | 39660283 |
| 4054 | 8 | 0.9998 | Ecological impact of antibiotic use in animals on different complex microflora: environment. Different means of interaction between microecological systems in different animal hosts (including humans) and the environment may occur during the transfer of resistant bacteria and their resistance genes. Spread of resistance takes place in different ways with respect to clonal spread of resistance strains by the spread of wide host range plasmids and translocatable elements. Commensals in ecosystems have a special significance and a pronounced capacity for acquisition and transfer of resistance genes as with Enterococcus faecium and Escherichia coli in the gut flora or Pseudomonas spp. in aquatic environments. The route of transmission from animals to humans by meat products is well established. Other routes via water and food plants (vegetables) have been investigated less, although resistance genes transfer in aquatic environments as evidenced from sequence comparison of such genes (e.g. tetR, floR in Salmonella typhimurium DT104). Whether this is due to rare but important transfer events or whether there is a more frequent exchange in aquatic or terrestrial environments needs further elucidation. | 2000 | 10794954 |
| 3341 | 9 | 0.9998 | The shared resistome of human and pig microbiota is mobilized by distinct genetic elements. 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. | 2021 | 33310720 |
| 3902 | 10 | 0.9997 | Integrons and antibiotic resistance genes in water-borne pathogens: threat detection and risk assessment. Antibiotic-resistant genes (ARGs) are regarded as emerging environmental pollutants and pose a serious health risk to the human population. Integrons are genetic elements that are involved in the spread of ARGs amongst bacterial species. They also act as reservoirs of these resistance traits, further contributing to the development of multi-drug resistance in several water-borne pathogens. Due to inter- and intra-species transfer, integrons are now commonly reported in important water-borne pathogens such as Vibrio, Campylobacter, Salmonella, Shigella, Escherichia coli and other opportunistic pathogens. These pathogens exhibit immense diversity in their resistance gene cassettes. The evolution of multiple novel and complex gene cassettes in integrons further suggests the selection and horizontal transfer of ARGs in multi-drug resistant bacteria. Thus, the detection and characterization of these integrons in water-borne pathogens, especially in epidemic and pandemic strains, is of the utmost importance. It will provide a framework in which health authorities can conduct improved surveillance of antibiotic resistance in our natural water bodies. Such a study will also be helpful in developing better strategies for the containment and cure of infections caused by these bacteria. | 2019 | 30990401 |
| 3915 | 11 | 0.9997 | Phylogenetic signature of lateral exchange of genes for antibiotic production and resistance among bacteria highlights a pattern of global transmission of pathogens between humans and livestock. The exchange of bacterial virulence factors driven by lateral gene transfer (LGT) can help indicate possible bacterial transmission among different hosts. Specifically, overlaying the phylogenetic signal of LGT among bacteria onto the distribution of respective isolation sources (hosts) can indicate patterns of transmission among these hosts. Here, we apply this approach towards a better understanding of patterns of bacterial transmission between humans and livestock. We utilize comparative genomics to trace patterns of LGT for an 11-gene operon responsible for the production of the antibiotic nisin and infer transmission of bacteria among respective host species. A total of 147 bacterial genomes obtained from NCBI were determined to contain the complete operon. Isolated from human, porcine and bovine hosts, these genomes represented six Streptococcus and one Staphylococcus species. Phylogenetic analyses of the operon sequences revealed a signature of frequent and recent lateral gene transfer that indicated extensive bacterial transmission between humans and pigs. For 11 isolates, we detected a Tn916-like transposon inserted into the operon. The transposon contained the tetM gene (tetracycline resistance) and additional phylogenetic analyses indicated transmission among human and animal hosts. The bacteria possessing the nisin operon and transposon were isolated from hosts distributed globally. These findings possibly reflect both the globalization of the food industry and an increasingly mobile and expanding human population. In addition to concerns regarding zoonosis, these findings also highlight the potential threat to livestock worldwide due to reverse zoonosis. | 2018 | 29631053 |
| 3914 | 12 | 0.9997 | Genomic Insights into Drug Resistance and Virulence Platforms, CRISPR-Cas Systems and Phylogeny of Commensal E. coli from Wildlife. Commensal bacteria act as important reservoirs of virulence and resistance genes. However, existing data are generally only focused on the analysis of human or human-related bacterial populations. There is a lack of genomic studies regarding commensal bacteria from hosts less exposed to antibiotics and other selective forces due to human activities, such as wildlife. In the present study, the genomes of thirty-eight E. coli strains from the gut of various wild animals were sequenced. The analysis of their accessory genome yielded a better understanding of the role of the mobilome on inter-bacterial dissemination of mosaic virulence and resistance plasmids. The study of the presence and composition of the CRISPR/Cas systems in E. coli from wild animals showed some viral and plasmid sequences among the spacers, as well as the relationship between CRISPR/Cas and E. coli phylogeny. Further, we constructed a single nucleotide polymorphisms-based core tree with E. coli strains from different sources (humans, livestock, food and extraintestinal environments). Bacteria from humans or highly human-influenced settings exhibit similar genetic patterns in CRISPR-Cas systems, plasmids or virulence/resistance genes-carrying modules. These observations, together with the absence of significant genetic changes in their core genome, suggest an ongoing flow of both mobile elements and E. coli lineages between human and natural ecosystems. | 2021 | 34063152 |
| 4165 | 13 | 0.9997 | A modular master on the move: the Tn916 family of mobile genetic elements. The Tn916 family is a group of mobile genetic elements that are widespread among many commensal and pathogenic bacteria. These elements are found primarily, but not exclusively, in the Firmicutes. They are integrated into the bacterial genome and are capable of conjugative transfer to a new host and, often, intracellular transposition to a different genomic site - hence their name: 'conjugative transposons', or 'integrative conjugative elements'. An increasing variety of Tn916 relatives are being reported from different bacteria, harbouring genes coding for resistance to various antibiotics and the potential to encode other functions, such as lantibiotic immunity. This family of mobile genetic elements has an extraordinary ability to acquire accessory genes, making them important vectors in the dissemination of various traits among environmental, commensal and clinical bacteria. These elements are also responsible for genome rearrangements, providing considerable raw material on which natural selection can act. Therefore, the study of this family of mobile genetic elements is essential for a better understanding and control of the current rise of antibiotic resistance among pathogenic bacteria. | 2009 | 19464182 |
| 3335 | 14 | 0.9997 | Population genomics and antimicrobial resistance dynamics of Escherichia coli in wastewater and river environments. Aquatic environments are key niches for the emergence, evolution and dissemination of antimicrobial resistance. However, the population diversity and the genetic elements that drive the dynamics of resistant bacteria in different aquatic environments are still largely unknown. The aim of this study was to understand the population genomics and evolutionary events of Escherichia coli resistant to clinically important antibiotics including aminoglycosides, in anthropogenic and natural water ecosystems. Here we show that less different E. coli sequence types (STs) are identified in wastewater than in rivers, albeit more resistant to antibiotics, and with significantly more plasmids/cell (6.36 vs 3.72). However, the genomic diversity within E. coli STs in both aquatic environments is similar. Wastewater environments favor the selection of conserved chromosomal structures associated with diverse flexible plasmids, unraveling promiscuous interplasmidic resistance genes flux. On the contrary, the key driver for river E. coli adaptation is a mutable chromosome along with few plasmid types shared between diverse STs harboring a limited resistance gene content. | 2021 | 33846529 |
| 3337 | 15 | 0.9997 | Evidence for wastewaters as environments where mobile antibiotic resistance genes emerge. The emergence and spread of mobile antibiotic resistance genes (ARGs) in pathogens have become a serious threat to global health. Still little is known about where ARGs gain mobility in the first place. Here, we aimed to collect evidence indicating where such initial mobilization events of clinically relevant ARGs may have occurred. We found that the majority of previously identified origin species did not carry the mobilizing elements that likely enabled intracellular mobility of the ARGs, suggesting a necessary interplay between different bacteria. Analyses of a broad range of metagenomes revealed that wastewaters and wastewater-impacted environments had by far the highest abundance of both origin species and corresponding mobilizing elements. Most origin species were only occasionally detected in other environments. Co-occurrence of origin species and corresponding mobilizing elements were rare in human microbiota. Our results identify wastewaters and wastewater-impacted environments as plausible arenas for the initial mobilization of resistance genes. | 2023 | 36966231 |
| 4562 | 16 | 0.9997 | The Dynamics of the Antimicrobial Resistance Mobilome of Salmonella enterica and Related Enteric Bacteria. The foodborne pathogen Salmonella enterica is considered a global public health risk. Salmonella enterica isolates can develop resistance to several antimicrobial drugs due to the rapid spread of antimicrobial resistance (AMR) genes, thus increasing the impact on hospitalization and treatment costs, as well as the healthcare system. Mobile genetic elements (MGEs) play key roles in the dissemination of AMR genes in S. enterica isolates. Multiple phenotypic and molecular techniques have been utilized to better understand the biology and epidemiology of plasmids including DNA sequence analyses, whole genome sequencing (WGS), incompatibility typing, and conjugation studies of plasmids from S. enterica and related species. Focusing on the dynamics of AMR genes is critical for identification and verification of emerging multidrug resistance. The aim of this review is to highlight the updated knowledge of AMR genes in the mobilome of Salmonella and related enteric bacteria. The mobilome is a term defined as all MGEs, including plasmids, transposons, insertion sequences (ISs), gene cassettes, integrons, and resistance islands, that contribute to the potential spread of genes in an organism, including S. enterica isolates and related species, which are the focus of this review. | 2022 | 35432284 |
| 9836 | 17 | 0.9997 | Staphylococcus aureus mobile genetic elements. Among the bacteria groups, most of them are known to be beneficial to human being whereas only a minority is being recognized as harmful. The pathogenicity of bacteria is due, in part, to their rapid adaptation in the presence of selective pressures exerted by the human host. In addition, through their genomes, bacteria are subject to mutations, various rearrangements or horizontal gene transfer among and/or within bacterial species. Bacteria's essential metabolic functions are generally encoding by the core genes. Apart of the core genes, there are several number of mobile genetic elements (MGE) acquired by horizontal gene transfer that might be beneficial under certain environmental conditions. These MGE namely bacteriophages, transposons, plasmids, and pathogenicity islands represent about 15% Staphylococcus aureus genomes. The acquisition of most of the MGE is made by horizontal genomic islands (GEI), recognized as discrete DNA segments between closely related strains, transfer. The GEI contributes to the wide spread of microorganisms with an important effect on their genome plasticity and evolution. The GEI are also involve in the antibiotics resistance and virulence genes dissemination. In this review, we summarize the mobile genetic elements of S. aureus. | 2014 | 24728610 |
| 4658 | 18 | 0.9997 | Class 1 integrons potentially predating the association with tn402-like transposition genes are present in a sediment microbial community. Integrons are genetic elements that contribute to lateral gene transfer in bacteria as a consequence of possessing a site-specific recombination system. This system facilitates the spread of genes when they are part of mobile cassettes. Most integrons are contained within chromosomes and are confined to specific bacterial lineages. However, this is not the case for class 1 integrons, which were the first to be identified and are one of the single biggest contributors to multidrug-resistant nosocomial infections, carrying resistance to many antibiotics in diverse pathogens on a global scale. The rapid spread of class 1 integrons in the last 60 years is partly a result of their association with a specific suite of transposition functions, which has facilitated their recruitment by plasmids and other transposons. The widespread use of antibiotics has acted as a positive selection pressure for bacteria, especially pathogens, which harbor class 1 integrons and their associated antibiotic resistance genes. Here, we have isolated bacteria from soil and sediment in the absence of antibiotic selection. Class 1 integrons were recovered from four different bacterial species not known to be human pathogens or commensals. All four integrons lacked the transposition genes previously considered to be a characteristic of this class. At least two of these integrons were located on a chromosome, and none of them possessed antibiotic resistance genes. We conclude that novel class 1 integrons are present in a sediment environment in various bacteria of the beta-proteobacterial class. These data suggest that the dispersal of this class may have begun before the "antibiotic era." | 2006 | 16885440 |
| 4659 | 19 | 0.9997 | Evidence for dynamic exchange of qac gene cassettes between class 1 integrons and other integrons in freshwater biofilms. Class 1 integrons carried by pathogens have acquired over 100 different gene cassettes encoding resistance to antimicrobial compounds, helping to generate a crisis in the management of infectious disease. It is presumed that these cassettes originated from environmental bacteria, but exchange of gene cassettes has surprisingly never been demonstrated outside laboratory or clinical contexts. We aimed to identify a natural environment where such exchanges might occur, and determine the phylogenetic range of participating integrons. Here we examine freshwater biofilms and show that families of cassettes conferring resistance to quaternary ammonium compounds (qac) are found on class 1 integrons identical to those from clinical contexts, on sequence variants of class 1 integrons only known from natural environments, and on other diverse classes of integrons only known from the chromosomes of soil and freshwater Proteobacteria. We conclude that gene cassettes might be readily shared between different integron classes found in environmental, commensal and pathogenic bacteria. This suggests that class 1 integrons in pathogens have access to a vast pool of gene cassettes, any of which could confer a phenotype of clinical relevance. Exploration of this resource might allow identification of resistance or virulence genes before they become part of multi-drug-resistant human pathogens. | 2009 | 19459951 |