# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 9824 | 0 | 1.0000 | Transposons: the agents of antibiotic resistance in bacteria. Transposons are a group of mobile genetic elements that are defined as a DNA sequence. Transposons can jump into different places of the genome; for this reason, they are called jumping genes. However, some transposons are always kept at the insertion site in the genome. Most transposons are inactivated and as a result, cannot move. Transposons are divided into two main groups: retrotransposons (class І) and DNA transposons (class ІІ). Retrotransposons are often found in eukaryotes. DNA transposons can be found in both eukaryotes and prokaryotes. The bacterial transposons belong to the DNA transposons and the Tn family, which are usually the carrier of additional genes for antibiotic resistance. Transposons can transfer from a plasmid to other plasmids or from a DNA chromosome to plasmid and vice versa that cause the transmission of antibiotic resistance genes in bacteria. The treatment of bacterial infectious diseases is difficult because of existing antibiotic resistance that part of this antibiotic resistance is caused by transposons. Bacterial infectious diseases are responsible for the increasing rise in world mortality rate. In this review, transposons and their roles have been studied in bacterial antibiotic resistance, in detail. | 2018 | 30113080 |
| 4134 | 1 | 0.9998 | Plasmid-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. | 2014 | 26104453 |
| 9828 | 2 | 0.9998 | Antibiotic resistance: genetic mechanisms and mobility. Based on the current knowledge, resistance genes seems mainly to originate in the organisms which produce antibiotics (Davies 1994). We lack considerably in the understanding of how these genes were transferred to pathogenic bacteria, and due to the enormous diversity of e.g. the soil flora, it is doubtful that we will ever obtain more that a faint picture of this. In Gram negative bacteria, more and more resistance genes are demonstrated to be located in integrons (e.g. beta-lactamase and streptomycin resistance genes in Salmonella Typhimurium DT104 (Sandvang et al. in press)). Integrons seem primarily to act as insertion sites for resistance genes. The origin of integrons as well as the resistance gene cassettes that are the other essential element of this system, is largely unknown (Hall & Collis 1995). Integrons can be located in the chromosome, in transposons, which have the ability to copy them themselves to other DNA molecules, or on plasmids. The emergence of resistant bacteria normally happens because of selection for a resistant clone of bacteria. Several mechanisms, however, exists by which the resistance genes can be transferred from one bacteria to another. Conjugation, mediated by plasmids or conjugative transposons, is currently the most well established of these mechanisms. Still, however, the selection pressure created by the use of antibiotics determines whether bacteria that have newly acquired a resistance gene expand to dominate in the population or remains a blink in history. | 1999 | 10783713 |
| 9820 | 3 | 0.9998 | The Tn21 subgroup of bacterial transposable elements. The Tn3 family of transposable elements is probably the most successful group of mobile DNA elements in bacteria: there are many different but related members and they are widely distributed in gram-negative and gram-positive bacteria. The Tn21 subgroup of the Tn3 family contains closely related elements that provide most of the currently known variation in Tn3-like elements in gram-negative bacteria and that are largely responsible for the problem of multiple resistance to antibiotics in these organisms. This paper reviews the structure, the mechanism of transposition, the mode of acquisition of accessory genes, and the evolution of these elements. | 1990 | 1963947 |
| 4165 | 4 | 0.9998 | 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 |
| 9829 | 5 | 0.9998 | Promiscuous transfer of drug resistance in gram-negative bacteria. Bacterial conjugation is a major mechanism for the spread of antibiotic-resistance genes in pathogenic organisms. In gram-negative bacteria, broad-host-range drug-resistance plasmids mediate genetic exchange between many unrelated species. The mechanism of conjugation encoded by the broad-host-range IncP plasmid RK2 has been studied in detail. The location and sequence of the transfer origin of RK2 has been determined. Several barriers limit plasmid transfer between unrelated bacteria: interactions at the cell surface may prevent effective mating contact, restriction systems may degrade foreign DNA, or the plasmid may not replicate in the new host. RK2 has evolved specific mechanisms by which it overcomes these barriers; this plasmid can mediate the transfer of resistance to most gram-negative bacteria. | 1984 | 6143782 |
| 4133 | 6 | 0.9998 | Importance of integrons in the diffusion of resistance. Horizontal transfer of resistance genes is a successful mechanism for the transmission and dissemination of multiple drug resistance among bacterial pathogens. The impact of horizontally transmitted genetic determinants in the evolution of resistance is particularly evident when resistance genes are physically associated in clusters and transferred en bloc to the recipient cell. Recent advances in the molecular characterisation of antibiotic resistance mechanisms have highlighted the existence of genetic structures. called integrons, involved in the acquisition of resistance genes. These DNA elements have frequently been reported in multi-drug resistant strains isolated from animals and humans, and are located either on the bacterial chromosome or on broad-host-range plasmids. The role of integrons in the development of multiple resistance relies on their unique capacity to cluster and express drug resistance genes. Moreover, the spread of resistance genes among different replicons and their exchange between plasmid and bacterial chromosome are facilitated by the integration of integrons into transposable elements. The association of a highly efficient gene capture and expression system, together with the capacity for vertical and horizontal transmission of resistance genes represents a powerful weapon used by bacteria to combat the assault of antibiotics. | 2001 | 11432416 |
| 9309 | 7 | 0.9997 | Plasmid 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. | 2008 | 18193080 |
| 9825 | 8 | 0.9997 | Intercontinental spread of promiscuous mercury-resistance transposons in environmental bacteria. We demonstrate that horizontal spread of mer operons similar to worldwide spread of antibiotic-resistance genes in medically important bacteria occurred in bacteria found in ores, soils and waters. The spread was mediated by different transposons and plasmids. Some of the spreading transposons were damaged in different ways but this did not prevent their further spread. Certain transposons are mosaics composed of segments belonging to distinct sequence types. These mosaics arose as a result of homologous and site-specific recombination. Our data suggest that the mercury-resistance operons of Gram-negative environmental bacteria can be considered as a worldwide population composed of a relatively small number of distinct recombining clones shared, at least partially, by environmental and clinical bacteria. | 1997 | 9159519 |
| 9295 | 9 | 0.9997 | Biological activities specified by antibiotic resistance plasmids. Bacteria can display resistance to a wide spectrum of noxious agents and environmental conditions, and these properties are often mediated by genes located on extrachromosomal DNA elements called plasmids. Replication, vertical and horizontal transmission and evolution of these elements are discussed, and examples of the genes responsible for the resistance phenotypes are given. Selective forces that drive the evolution of new combinations of bacterial properties of particular importance in clinical situations are analysed. | 1986 | 3542928 |
| 4131 | 10 | 0.9997 | R plasmid transfer. This paper is a brief survey of the systems of genetic exchange in bacteria relevant to the spread of antibiotic resistance genes. Emphasis is given to those systems most likely to be important in nature, particularly conjugation. Several recently described examples of conjugation in Gram-positive bacteria are discussed and contrasted with the better studied examples in Gram-negative bacteria. | 1986 | 3542931 |
| 4164 | 11 | 0.9997 | Broad-host-range IncP-1 plasmids and their resistance potential. The plasmids of the incompatibility (Inc) group IncP-1, also called IncP, as extrachromosomal genetic elements can transfer and replicate virtually in all Gram-negative bacteria. They are composed of backbone genes that encode a variety of essential functions and accessory genes that have implications for human health and environmental bioremediation. Broad-host-range IncP plasmids are known to spread genes between distinct phylogenetic groups of bacteria. These genes often code for resistances to a broad spectrum of antibiotics, heavy metals, and quaternary ammonium compounds used as disinfectants. The backbone of these plasmids carries modules that enable them to effectively replicate, move to a new host via conjugative transfer and to be stably maintained in bacterial cells. The adaptive, resistance, and virulence genes are mainly located on mobile genetic elements integrated between the functional plasmid backbone modules. Environmental studies have demonstrated the wide distribution of IncP-like replicons in manure, soils and wastewater treatment plants. They also are present in strains of pathogenic or opportunistic bacteria, which can be a cause for concern, because they may encode multiresistance. Their broad distribution suggests that IncP plasmids play a crucial role in bacterial adaptation by utilizing horizontal gene transfer. This review summarizes the variety of genetic information and physiological functions carried by IncP plasmids, which can contribute to the spread of antibiotic and heavy metal resistance while also mediating the process of bioremediation of pollutants. Due to the location of the resistance genes on plasmids with a broad-host-range and the presence of transposons carrying these genes it seems that the spread of these genes would be possible and quite hazardous in infection control. Future studies are required to determine the level of risk of the spread of resistance genes located on these plasmids. | 2013 | 23471189 |
| 4175 | 12 | 0.9997 | Resistance 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. | 1996 | 8953105 |
| 4170 | 13 | 0.9997 | 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. | 2025 | 40098486 |
| 9308 | 14 | 0.9997 | Integrons: natural tools for bacterial genome evolution. Integrons were first identified as the primary mechanism for antibiotic resistance gene capture and dissemination among Gram-negative bacteria. More recently, their role in genome evolution has been extended with the discovery of larger integron structures, the super-integrons, as genuine components of the genomes of many species throughout the gamma-proteobacterial radiation. The functional platforms of these integrons appear to be sedentary, whereas their gene cassette contents are highly variable. Nevertheless, the gene cassettes for which an activity has been experimentally demonstrated encode proteins related to simple adaptive functions and their recruitment is seen as providing the bacterial host with a selective advantage. The widespread occurrence of the integron system among Gram-negative bacteria is discussed, with special focus on the super-integrons. Some of the adaptive functions encoded by these genes are also reviewed, and implications of integron-mediated genome evolution in the emergence of novel bacterial species are highlighted. | 2001 | 11587934 |
| 4132 | 15 | 0.9997 | Mobilization of transposons : rationale and techniques for detection. The ability to share genetic information with other bacteria represents one of the most important adaptive mechanisms available to bacteria pathogenic for humans. The exchange of many different types of genetic information appears to occur frequently and exchange of determinants responsible for antimicrobial resistance is the best studied, since the movements of resistance determinants are easy to follow and the clinical importance of resistance dissemination is so great. The most common vehicles by which bacteria exchange resistance determinants are plasmids and transposons. | 2001 | 21374427 |
| 9307 | 16 | 0.9997 | Integrons. Integrons are genetic elements able to acquire and rearrange open reading frames (ORFs) embedded in gene cassette units and convert them to functional genes by ensuring their correct expression. They were originally identified as a mechanism used by Gram-negative bacteria to collect antibiotic resistance genes and express multiple resistance phenotypes in synergy with transposons. More recently, their role has been broadened with the discovery of chromosomal integron (CI) structures in the genomes of hundreds of bacterial species. This review focuses on the resources carried in these elements, on their unique recombination mechanisms, and on the different mechanisms controlling the cassette dynamics. We discuss the role of the toxin/antitoxin (TA) cassettes for the stabilization of the large cassette arrays carried in the larger CIs, known as superintegrons. Finally, we explore the central role played by single-stranded DNA in the integron cassette dynamics in light of the recent discovery that the integron integrase expression is controlled by the SOS response. | 2010 | 20707672 |
| 9849 | 17 | 0.9997 | Analysis of antibiotic resistance regions in Gram-negative bacteria. Antibiotic resistance in Gram-negative bacteria is often due to the acquisition of resistance genes from a shared pool. In multiresistant isolates these genes, together with associated mobile elements, may be found in complex conglomerations on plasmids or on the chromosome. Analysis of available sequences reveals that these multiresistance regions (MRR) are modular, mosaic structures composed of different combinations of components from a limited set arranged in a limited number of ways. Components common to different MRR provide targets for homologous recombination, allowing these regions to evolve by combinatorial evolution, but our understanding of this process is far from complete. Advances in technology are leading to increasing amounts of sequence data, but currently available automated annotation methods usually focus on identifying ORFs and predicting protein function by homology. In MRR, where the genes are often well characterized, the challenge is to identify precisely which genes are present and to define the boundaries of complete and fragmented mobile elements. This review aims to summarize the types of mobile elements involved in multiresistance in Gram-negative bacteria and their associations with particular resistance genes, to describe common components of MRR and to illustrate methods for detailed analysis of these regions. | 2011 | 21564142 |
| 9827 | 18 | 0.9997 | Evolution of bacterial resistance to antibiotics during the last three decades. Bacterial resistance to antibiotics is often plasmid-mediated and the associated genes encoded by transposable elements. These elements play a central role in evolution by providing mechanisms for the generation of diversity and, in conjunction with DNA transfer systems, for the dissemination of resistances to other bacteria. At the University Hospital of Zaragoza, extensive efforts have been made to define both the dissemination and evolution of antibiotic resistance by studying the transferable R plasmids and transposable elements. Here we describe the research on bacterial resistance to antibiotics in which many authors listed in the references have participated. The aspects of bacterial resistance dealt with are: (i) transferable resistance mediated by R plasmids in Gram-negative bacteria, (ii) R plasmid-mediated resistance to apramycin and hygromycin in clinical strains, (iii) the transposon Tn1696 and the integron In4, (iv) expression of Escherichia coli resistance genes in Haemophilus influenzae, (v) aminoglycoside-modifying-enzymes in the genus Mycobacterium with no relation to resistance, and (vi) macrolide-resistance and new mechanisms developed by Gram-positive bacteria. | 1998 | 10943375 |
| 9310 | 19 | 0.9997 | Bacterial resistance to antibiotics. Effective antibacterial drugs have been available for nearly 50 years. After the introduction of each new such drug, whether chemically synthesized or a naturally occurring antibiotic, bacterial resistance to it has emerged. The genetic mechanisms by which bacteria have acquired resistance were quite unexpected; a new evolutionary pathways has been revealed. Although some antibiotic resistance has resulted from mutational changes in structural proteins--targets for the drugs' action--most has resulted from the acquisition of new, ready-made genes from an external source--that is, from another bacterium. Vectors of the resistance genes are plasmids--heritable DNA molecules that are transmissible between bacterial cells. Plasmids without antibiotic-resistance genes are common in all kinds of bacteria. Resistance plasmids have resulted from the insertion of new DNA sequences into previously existing plasmids. Thus, the spread of antibiotic resistance is at three levels: bacteria between people or animals; plasmids between bacteria; and transposable genes between plasmids. | 1984 | 6319093 |