The role of conjugative transposons in spreading antibiotic resistance between bacteria that inhabit the gastrointestinal tract. - Related Documents




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417401.0000The role of conjugative transposons in spreading antibiotic resistance between bacteria that inhabit the gastrointestinal tract. There is huge potential for genetic exchange to occur within the dense, diverse anaerobic microbial population inhabiting the gastrointestinal tract (GIT) of humans and animals. However, the incidence of conjugative transposons (CTns) and the antibiotic resistance genes they carry has not been well studied among this population. Since any incoming bacteria, including pathogens, can access this reservoir of genes, this oversight would appear to be an important one. Recent evidence has shown that anaerobic bacteria native to the rumen or hindgut harbour both novel antibiotic resistance genes and novel conjugative transposons. These CTns, and previously characterized CTns, can be transferred to a wide range of commensal bacteria under laboratory and in vivo conditions. The main evidence that gene transfer occurs widely in vivo between GIT bacteria, and between GIT bacteria and pathogenic bacteria, is that identical resistance genes are present in diverse bacterial species from different hosts.200212568333
417510.9999Resistance gene transfer in anaerobes: new insights, new problems. Investigations of antibiotic-resistance gene transfer elements in Bacteroides species have generated some new insights into how bacteria transfer resistance genes and what environmental conditions foster gene transfer. Integrated gene transfer elements, called conjugative transposons, appear to be responsible for much of the transfer of resistance genes among Bacteroides species. Conjugative transposons not only transfer themselves but also mobilize coresident plasmids and excise and mobilize unlinked integrated elements. Less is known about resistance gene transfer elements of the gram-positive anaerobes, but there are some indications that similar elements may be found in them as well. An unusual feature of the Bacteroides conjugative transposons is that transfer of many of them is stimulated considerably by low concentrations of antibiotics. Thus, antibiotics not only select for resistant strains but also can stimulate transfer of the resistance gene in the first place. This finding raises questions about whether use of low-dose tetracycline therapy may have a greater effect on the resident microflora than had been previously thought. Finally, investigations of resistance genes in Bacteroides species and other genera of bacteria have begun to provide evidence that the resident microflora of the human body does indeed act as a reservoir for resistance genes, which may be acquired from and passed on the transient colonizers of the site.19968953105
417220.9999Variation on a theme; an overview of the Tn916/Tn1545 family of mobile genetic elements in the oral and nasopharyngeal streptococci. The oral and nasopharyngeal streptococci are a major part of the normal microbiota in humans. Most human associated streptococci are considered commensals, however, a small number of them are pathogenic, causing a wide range of diseases including oral infections such as dental caries and periodontitis and diseases at other body sites including sinusitis and endocarditis, and in the case of Streptococcus pneumoniae, meningitis. Both phenotypic and sequence based studies have shown that the human associated streptococci from the mouth and nasopharynx harbor a large number of antibiotic resistance genes and these are often located on mobile genetic elements (MGEs) known as conjugative transposons or integrative and conjugative elements of the Tn916/Tn1545 family. These MGEs are responsible for the spread of the resistance genes between streptococci and also between streptococci and other bacteria. In this review we describe the resistances conferred by, and the genetic variations between the many different Tn916-like elements found in recent studies of oral and nasopharyngeal streptococci and show that Tn916-like elements are important mediators of antibiotic resistance genes within this genus. We will also discuss the role of the oral environment and how this is conducive to the transfer of these elements and discuss the contribution of both transformation and conjugation on the transfer and evolution of these elements in different streptococci.201425368607
417330.9999Evidence for natural horizontal transfer of tetQ between bacteria that normally colonize humans and bacteria that normally colonize livestock. Though numerous studies have shown that gene transfer occurs between distantly related bacterial genera under laboratory conditions, the frequency and breadth of horizontal transfer events in nature remain unknown. Previous evidence for natural intergeneric transfers came from studies of genes in human pathogens, bacteria that colonize the same host. We present evidence that natural transfer of a tetracycline resistance gene, tetQ, has occurred between bacterial genera that normally colonize different hosts. A DNA sequence comparative approach was taken to examine the extent of horizontal tetQ dissemination between species of Bacteroides, the predominant genus of the human colonic microflora, and between species of Bacteroides and of the distantly related genus Prevotella, a predominant genus of the microflora of the rumens and intestinal tracts of farm animals. Virtually identical tetQ sequences were found in a number of isolate pairs differing in taxonomy and geographic origin, indicating that extensive natural gene transmission has occurred. Among the exchange events indicated by the evidence was the very recent transfer of an allele of tetQ usually found in Prevotella spp. to a Bacteroides fragilis strain.19947944364
416540.9999A 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.200919464182
413450.9998Plasmid-Mediated Antimicrobial Resistance in Staphylococci and Other Firmicutes. In staphylococci and other Firmicutes, resistance to numerous classes of antimicrobial agents, which are commonly used in human and veterinary medicine, is mediated by genes that are associated with mobile genetic elements. The gene products of some of these antimicrobial resistance genes confer resistance to only specific members of a certain class of antimicrobial agents, whereas others confer resistance to the entire class or even to members of different classes of antimicrobial agents. The resistance mechanisms specified by the resistance genes fall into any of three major categories: active efflux, enzymatic inactivation, and modification/replacement/protection of the target sites of the antimicrobial agents. Among the mobile genetic elements that carry such resistance genes, plasmids play an important role as carriers of primarily plasmid-borne resistance genes, but also as vectors for nonconjugative and conjugative transposons that harbor resistance genes. Plasmids can be exchanged by horizontal gene transfer between members of the same species but also between bacteria belonging to different species and genera. Plasmids are highly flexible elements, and various mechanisms exist by which plasmids can recombine, form cointegrates, or become integrated in part or in toto into the chromosomal DNA or into other plasmids. As such, plasmids play a key role in the dissemination of antimicrobial resistance genes within the gene pool to which staphylococci and other Firmicutes have access. This chapter is intended to provide an overview of the current knowledge of plasmid-mediated antimicrobial resistance in staphylococci and other Firmicutes.201426104453
416860.9998Various pathways leading to the acquisition of antibiotic resistance by natural transformation. Natural transformation can lead to exchange of DNA between taxonomically diverse bacteria. In the case of chromosomal DNA, homology-based recombination with the recipient genome is usually necessary for heritable stability. In our recent study, we have shown that natural transformation can promote the transfer of transposons, IS elements, and integrons and gene cassettes, largely independent of the genetic relationship between the donor and recipient bacteria. Additional results from our study suggest that natural transformation with species-foreign DNA might result in the uptake of a wide range of DNA fragments; leading to changes in the antimicrobial susceptibility profile and contributing to the generation of antimicrobial resistance in bacteria.201223482877
983670.9998Staphylococcus 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.201424728610
417080.9998The 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.202540098486
930990.9998Plasmid encoded antibiotic resistance: acquisition and transfer of antibiotic resistance genes in bacteria. Bacteria have existed on Earth for three billion years or so and have become adept at protecting themselves against toxic chemicals. Antibiotics have been in clinical use for a little more than 6 decades. That antibiotic resistance is now a major clinical problem all over the world attests to the success and speed of bacterial adaptation. Mechanisms of antibiotic resistance in bacteria are varied and include target protection, target substitution, antibiotic detoxification and block of intracellular antibiotic accumulation. Acquisition of genes needed to elaborate the various mechanisms is greatly aided by a variety of promiscuous gene transfer systems, such as bacterial conjugative plasmids, transposable elements and integron systems, that move genes from one DNA system to another and from one bacterial cell to another, not necessarily one related to the gene donor. Bacterial plasmids serve as the scaffold on which are assembled arrays of antibiotic resistance genes, by transposition (transposable elements and ISCR mediated transposition) and site-specific recombination mechanisms (integron gene cassettes).The evidence suggests that antibiotic resistance genes in human bacterial pathogens originate from a multitude of bacterial sources, indicating that the genomes of all bacteria can be considered as a single global gene pool into which most, if not all, bacteria can dip for genes necessary for survival. In terms of antibiotic resistance, plasmids serve a central role, as the vehicles for resistance gene capture and their subsequent dissemination. These various aspects of bacterial resistance to antibiotics will be explored in this presentation.200818193080
4045100.9998Bacterial resistance to antimicrobial agents and its impact on veterinary and human medicine. BACKGROUND: Antimicrobial resistance has become a major challenge in veterinary medicine, particularly in the context of bacterial pathogens that play a role in both humans and animals. OBJECTIVES: This review serves as an update on acquired resistance mechanisms in bacterial pathogens of human and animal origin, including examples of transfer of resistant pathogens between hosts and of resistance genes between bacteria. RESULTS: Acquired resistance is based on resistance-mediating mutations or on mobile resistance genes. Although mutations are transferred vertically, mobile resistance genes are also transferred horizontally (by transformation, transduction or conjugation/mobilization), contributing to the dissemination of resistance. Mobile genes specifying any of the three major resistance mechanisms - enzymatic inactivation, reduced intracellular accumulation or modification of the cellular target sites - have been found in a variety of bacteria that may be isolated from animals. Such resistance genes are associated with plasmids, transposons, gene cassettes, integrative and conjugative elements or other mobile elements. Bacteria, including zoonotic pathogens, can be exchanged between animals and humans mainly via direct contact, but also via dust, aerosols or foods. Proof of the direction of transfer of resistant bacteria can be difficult and depends on the location of resistance genes or mutations in the chromosomal DNA or on a mobile element. CONCLUSION: The wide variety in resistance and resistance transfer mechanisms will continue to ensure the success of bacterial pathogens in the future. Our strategies to counteract resistance and preserve the efficacy of antimicrobial agents need to be equally diverse and resourceful.201727581211
4041110.9998The human gut resistome. In recent decades, the emergence and spread of antibiotic resistance among bacterial pathogens has become a major threat to public health. Bacteria can acquire antibiotic resistance genes by the mobilization and transfer of resistance genes from a donor strain. The human gut contains a densely populated microbial ecosystem, termed the gut microbiota, which offers ample opportunities for the horizontal transfer of genetic material, including antibiotic resistance genes. Recent technological advances allow microbiota-wide studies into the diversity and dynamics of the antibiotic resistance genes that are harboured by the gut microbiota ('the gut resistome'). Genes conferring resistance to antibiotics are ubiquitously present among the gut microbiota of humans and most resistance genes are harboured by strictly anaerobic gut commensals. The horizontal transfer of genetic material, including antibiotic resistance genes, through conjugation and transduction is a frequent event in the gut microbiota, but mostly involves non-pathogenic gut commensals as these dominate the microbiota of healthy individuals. Resistance gene transfer from commensals to gut-dwelling opportunistic pathogens appears to be a relatively rare event but may contribute to the emergence of multi-drug resistant strains, as is illustrated by the vancomycin resistance determinants that are shared by anaerobic gut commensals and the nosocomial pathogen Enterococcus faecium.201525918444
4255120.9998Oral biofilms: a reservoir of transferable, bacterial, antimicrobial resistance. Oral microbes are responsible for dental caries and periodontal diseases and have also been implicated in a range of other diseases beyond the oral cavity. These bacteria live primarily as complex, polymicrobial biofilms commonly called dental plaque. Cells growing within a biofilm often exhibit altered phenotypes, such as increased antibiotic resistance. The stable structural properties and close proximity of the bacterial cells within the biofilm appears to be an excellent environment for horizontal gene transfer, which can lead to the spread of antibiotic resistance genes amongst the biofilm inhabitants. This article will present an overview of the different types and amount of resistance to antibiotics that have been found in the human oral microbiota and will discuss the oral inhabitants' role as a reservoir of antimicrobial resistance genes. In addition, data on the genetic support for these resistance genes will be detailed and the evidence for horizontal gene transfer reviewed, demonstrating that the bacteria inhabiting the oral cavity are a reservoir of transferable antibiotic resistance.201021133668
9652130.9998Transfer and Persistence of a Multi-Drug Resistance Plasmid in situ of the Infant Gut Microbiota in the Absence of Antibiotic Treatment. The microbial ecosystem residing in the human gut is believed to play an important role in horizontal exchange of virulence and antibiotic resistance genes that threatens human health. While the diversity of gut-microorganisms and their genetic content has been studied extensively, high-resolution insight into the plasticity, and selective forces shaping individual genomes is scarce. In a longitudinal study, we followed the dynamics of co-existing Escherichia coli lineages in an infant not receiving antibiotics. Using whole genome sequencing, we observed large genomic deletions, bacteriophage infections, as well as the loss and acquisition of plasmids in these lineages during their colonization of the human gut. In particular, we captured the exchange of multidrug resistance genes, and identified a clinically relevant conjugative plasmid mediating the transfer. This resistant transconjugant lineage was maintained for months, demonstrating that antibiotic resistance genes can disseminate and persist in the gut microbiome; even in absence of antibiotic selection. Furthermore, through in vivo competition assays, we suggest that the resistant transconjugant can persist through a fitness advantage in the mouse gut in spite of a fitness cost in vitro. Our findings highlight the dynamic nature of the human gut microbiota and provide the first genomic description of antibiotic resistance gene transfer between bacteria in the unperturbed human gut. These results exemplify that conjugative plasmids, harboring resistance determinants, can transfer and persists in the gut in the absence of antibiotic treatment.201729018426
4222140.9998Conjugal Transfer of Antibiotic Resistances in Lactobacillus spp. Lactic acid bacteria (LAB) are a heterogeneous group of bacteria which are Gram-positive, facultative anaerobes and non-motile, non-spore forming, with varied shapes from cocci to coccobacilli and bacilli. Lactobacillus is the largest and most widely used bacterial species amongst LAB in fermented foods and beverages. The genus is a common member of human gut microbiome. Several species are known to provide benefits to the human gut via synergistic interactions with the gut microbiome and their ability to survive the gut environment. This ability to confer positive health effects provide them a status of generally recognized as safe (GRAS) microorganisms. Due to their various beneficial characteristics, other factors such as their resistance acquisition were overlooked. Overuse of antibiotics has made certain bacteria develop resistance against these drugs. Antibiotic resistance was found to be acquired mainly through conjugation which is a type of lateral gene transfer. Several in vitro methods of conjugation have been discussed previously depending on their success to transfer resistance. In this review, we have addressed methods that are employed to study the transfer of resistance genes using the conjugation phenomenon in lactobacilli.202134076710
4044150.9998Antibiotic resistance in food-related bacteria--a result of interfering with the global web of bacterial genetics. A series of antibiotic resistance genes have been sequenced and found to be identical or nearly identical in various ecological environments. Similarly, genetic vectors responsible for assembly and mobility of antibiotic resistance genes, such as transposons, integrons and R plasmids of similar or identical type are also widespread in various niches of the environment. Many zoonotic bacteria carry antibiotic resistance genes directly from different food-producing environments to the human being. These circumstances may have a major impact on the degree for success in treating infectious diseases in man. Several recent examples demonstrate that use of antibiotics in all parts of the food production chain contributes to the increasing level of antibiotic resistance among the food-borne pathogenic bacteria. Modern industrialized food production adds extra emphasis on lowering the use of antibiotics in all parts of agriculture, husbandry and fish farming because these food products are distributed to very large numbers of humans compared to more traditional smaller scale niche production.200212222637
4038160.9998Environmental macrolide-lincosamide-streptogramin and tetracycline resistant bacteria. Bacteria can become resistant to antibiotics by mutation, transformation, and/or acquisition of new genes which are normally associated with mobile elements (plasmids, transposons, and integrons). Mobile elements are the main driving force in horizontal gene transfer between strains, species, and genera and are responsible for the rapid spread of particular elements throughout a bacterial community and between ecosystems. Today, antibiotic resistant bacteria are widely distributed throughout the world and have even been isolated from environments that are relatively untouched by human civilization. In this review macrolides, lincosamides, streptogramins, and tetracycline resistance genes and bacteria will be discussed with an emphasis on the resistance genes which are unique to environmental bacteria which are defined for this review as species and genera that are primarily found outside of humans and animals.201121833302
3834170.9998What antimicrobial resistance has taught us about horizontal gene transfer. Horizontal gene transfer (HGT) has been responsible for the dissemination of numerous antimicrobial-resistance determinants throughout diverse bacterial species. The rapid and broad dissemination of resistance determinants by HGT, and subsequent selection for resistance imposed by the use of antimicrobials, threatens to undermine the usefulness of antimicrobials. However, vigilant surveillance of the emerging antimicrobial resistance in clinical settings and subsequent studies of resistant isolates create a powerful system for studying HGT and detecting rare events. Two of the most closely monitored phenotypes are resistance to beta-lactams and resistance to fluoroquinolones. Studies of resistance to these antimicrobials have revealed that (1) transformation occurs between different species of bacteria including some recipient species that were not previously known to be competent for natural transformation; (2) transduction may be playing an important role in generating novel methicillin-resistant Staphylococcus aureus (MRSA) strains, although the details of transferring the SCCmec element are not yet fully understood; (3) Resistance genes are probably moving to plasmids from chromosomes more rapidly than in the past; and (4) Resistance genes are aggregating upon plasmids. The linkage of numerous resistance genes on individual plasmids may underlie the persistence of resistance to specific antimicrobials even when use of those antimicrobials is discontinued. Further studies of HGT and methods for controlling HGT may be necessary to maintain the usefulness of antimicrobials.200919271198
4054180.9998Ecological 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.200010794954
4034190.9998Environmental and clinical antibiotic resistomes, same only different. The history of antibiotic use in the clinic is one of initial efficacy followed inevitably by the emergence of resistance. Often this resistance is the result of the capture and mobilization of genes that have their origins in environmental reservoirs. Both antibiotic production and resistance are ancient and widely distributed among microbes in the environment. This deep reservoir of resistance offers the opportunity for gene flow into susceptible disease-causing bacteria. Not all resistance genes are equally successfully mobilized, and some dominate in the clinic. The differences and similarities in resistance mechanisms and associated genes among environments reveal a complex interplay between gene capture and mobilization that requires study of gene diversity and gene product function to fully understand the breadth and depth of resistance and the risk to human health.201931330416