The complete genome sequences of four new IncN plasmids from wastewater treatment plant effluent provide new insights into IncN plasmid diversity and evolution. - Related Documents




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996501.0000The complete genome sequences of four new IncN plasmids from wastewater treatment plant effluent provide new insights into IncN plasmid diversity and evolution. The dissemination of antibiotic resistance genes among bacteria often occurs by means of plasmids. Wastewater treatment plants (WWTP) were previously recognized as hot spots for the horizontal transfer of genetic material. One of the plasmid groups that is often associated with drug resistance is the incompatibility group IncN. The aim of this study was to gain insights into the diversity and evolutionary history of IncN plasmids by determining and comparing the complete genome sequences of the four novel multi-drug resistance plasmids pRSB201, pRSB203, pRSB205 and pRSB206 that were exogenously isolated from the final effluent of a municipal WWTP. Their sizes range between 42,875 bp and 56,488 bp and they share a common set of backbone modules that encode plasmid replication initiation, conjugative transfer, and plasmid maintenance and control. All plasmids are transferable at high rates between Escherichia coli strains, but did not show a broad host range. Different genes conferring resistances to ampicillin, streptomycin, spectinomycin, sulfonamides, tetracycline and trimethoprim were identified in accessory modules inserted in these plasmids. Comparative analysis of the four WWTP IncN plasmids and IncN plasmids deposited in the NCBI database enabled the definition of a core set of backbone genes for this group. Moreover, this approach revealed a close phylogenetic relationship between the IncN plasmids isolated from environmental and clinical samples. Phylogenetic analysis also suggests the existence of host-specific IncN plasmid subgroups. In conclusion, IncN plasmids likely contribute to the dissemination of resistance determinants between environmental bacteria and clinical strains. This is of particular importance since multi-drug resistance IncN plasmids have been previously identified in members of the Enterobacteriaceae that cause severe infections in humans.201222326849
996410.9998Diversity and Global Distribution of IncL/M Plasmids Enabling Horizontal Dissemination of β-Lactam Resistance Genes among the Enterobacteriaceae. Antibiotic resistance determinants are frequently associated with plasmids and other mobile genetic elements, which simplifies their horizontal transmission. Several groups of plasmids (including replicons of the IncL/M incompatibility group) were found to play an important role in the dissemination of resistance genes encoding β-lactamases. The IncL/M plasmids are large, broad host range, and self-transmissible replicons. We have identified and characterized two novel members of this group: pARM26 (isolated from bacteria inhabiting activated sludge from a wastewater treatment plant) and pIGT15 (originating from a clinical strain of Escherichia coli). This instigated a detailed comparative analysis of all available sequences of IncL/M plasmids encoding β-lactamases. The core genome of these plasmids is comprised of 20 genes with conserved synteny. Phylogenetic analyses of these core genes allowed clustering of the plasmids into four separate groups, which reflect their antibiotic resistance profiles. Examination of the biogeography of the IncL/M plasmids revealed that they are most frequently found in bacteria of the family Enterobacteriaceae originating from the Mediterranean region and Western Europe and that they are able to persist in various ecological niches even in the absence of direct antibiotic selection pressure.201526236726
997320.9998Spread and Persistence of Virulence and Antibiotic Resistance Genes: A Ride on the F Plasmid Conjugation Module. The F plasmid or F-factor is a large, 100-kbp, circular conjugative plasmid of Escherichia coli and was originally described as a vector for horizontal gene transfer and gene recombination in the late 1940s. Since then, F and related F-like plasmids have served as role models for bacterial conjugation. At present, more than 200 different F-like plasmids with highly related DNA transfer genes, including those for the assembly of a type IV secretion apparatus, are completely sequenced. They belong to the phylogenetically related MOB(F12)A group. F-like plasmids are present in enterobacterial hosts isolated from clinical as well as environmental samples all over the world. As conjugative plasmids, F-like plasmids carry genetic modules enabling plasmid replication, stable maintenance, and DNA transfer. In this plasmid backbone of approximately 60 kbp, the DNA transfer genes occupy the largest and mostly conserved part. Subgroups of MOB(F12)A plasmids can be defined based on the similarity of TraJ, a protein required for DNA transfer gene expression. In addition, F-like plasmids harbor accessory cargo genes, frequently embedded within transposons and/or integrons, which harness their host bacteria with antibiotic resistance and virulence genes, causing increasingly severe problems for the treatment of infectious diseases. Here, I focus on key genetic elements and their encoded proteins present on the F-factor and other typical F-like plasmids belonging to the MOB(F12)A group of conjugative plasmids.201830022749
996630.9998The A to Z of A/C plasmids. Plasmids belonging to incompatibility groups A and C (now A/C) were among the earliest to be associated with antibiotic resistance in Gram-negative bacteria. A/C plasmids are large, conjugative plasmids with a broad host range. The prevalence of A/C plasmids in collections of clinical isolates has revealed their importance in the dissemination of extended-spectrum β-lactamases and carbapenemases. They also mobilize SGI1-type resistance islands. Revived interest in the family has yielded many complete A/C plasmid sequences, revealing that RA1, designated A/C1, is different from the remainder, designated A/C2. There are two distinct A/C2 lineages. Backbones of 128-130 kb include over 120 genes or ORFs encoding proteins of at least 100 amino acids, but very few have been characterized. Genes potentially required for replication, stability and transfer have been identified, but only the replication system of RA1 and the regulation of transfer have been studied. There is enormous variety in the antibiotic resistance genes carried by A/C2 plasmids but they are usually clustered in larger regions at various locations in the backbone. The ARI-A and ARI-B resistance islands are always at a specific location but have variable content. ARI-A is only found in type 1 A/C2 plasmids, which disseminate blaCMY-2 and blaNDM-1 genes, whereas ARI-B, carrying the sul2 gene, is found in both type 1 and type 2. This review summarizes current knowledge of A/C plasmids, and highlights areas of research to be considered in the future.201525910948
446540.9998Genetic analyses of sulfonamide resistance and its dissemination in gram-negative bacteria illustrate new aspects of R plasmid evolution. In contrast to what has been observed for many other antibiotic resistance mechanisms, there are only two known genes encoding plasmid-borne sulfonamide resistance. Both genes, sulI and sulII, encode a drug-resistant dihydropteroate synthase enzyme. In members of the family Enterobacteriaceae isolated from several worldwide sources, plasmid-mediated resistance to sulfonamides could be identified by colony hybridization as being encoded by sulI, sulII, or both. The sulI gene was in all cases found to be located in the newly defined, mobile genetic element, recently named an integron, which has been shown to contain a site-specific recombination system for the integration of various antibiotic resistance genes. The sulII gene was almost exclusively found as part of a variable resistance region on small, nonconjugative plasmids. Colony hybridization to an intragenic probe, restriction enzyme digestion, and nucleotide sequence analysis of small plasmids indicated that the sulII gene and contiguous sequences represent an independently occurring region disseminated in the bacterial population. The sulII resistance region was bordered by direct repeats, which in some plasmids were totally or partially deleted. The prevalence of sulI and sulII could thus be accounted for by their stable integration in transposons and in plasmids that are widely disseminated among gram-negative bacteria.19911952855
997450.9998Role of Plasmids in Co-Selection of Antimicrobial Resistances Among Escherichia coli Isolated from Pigs. Co-selection is thought to occur when resistance genes are located on the same mobile genetic element. However, this mechanism is currently poorly understood. In this study, complete circular plasmids from swine-derived Escherichia coli were sequenced with short and long reads to confirm that resistance genes involved in co-resistance were co-transferred by the same plasmid. Conjugative transfer tests were performed, and multiple resistance genes were transmitted. The genes possessed by the donor, transconjugant, and plasmid of the donor were highly similar. In addition, the sequences of the plasmid of the donor and the plasmid of the transconjugant were almost identical. Resistance genes associated with statistically significant combinations of antimicrobial use and resistance were co-transmitted by the same plasmid. These results suggest that resistance genes may be involved in co-selection by their transfer between bacteria on the same plasmid.202337540099
988760.9998PCR-Based Analysis of ColE1 Plasmids in Clinical Isolates and Metagenomic Samples Reveals Their Importance as Gene Capture Platforms. ColE1 plasmids are important vehicles for the spread of antibiotic resistance in the Enterobacteriaceae and Pasteurellaceae families of bacteria. Their monitoring is essential, as they harbor important resistant determinants in humans, animals and the environment. In this work, we have analyzed ColE1 replicons using bioinformatic and experimental approaches. First, we carried out a computational study examining the structure of different ColE1 plasmids deposited in databases. Bioinformatic analysis of these ColE1 replicons revealed a mosaic genetic structure consisting of a host-adapted conserved region responsible for the housekeeping functions of the plasmid, and a variable region encoding a wide variety of genes, including multiple antibiotic resistance determinants. From this exhaustive computational analysis we developed a new PCR-based technique, targeting a specific sequence in the conserved region, for the screening, capture and sequencing of these small plasmids, either specific for Enterobacteriaceae or specific for Pasteurellaceae. To validate this PCR-based system, we tested various collections of isolates from both bacterial families, finding that ColE1 replicons were not only highly prevalent in antibiotic-resistant isolates, but also present in susceptible bacteria. In Pasteurellaceae, ColE1 plasmids carried almost exclusively antibiotic resistance genes. In Enterobacteriaceae, these plasmids encoded a large range of traits, including not only antibiotic resistance determinants, but also a wide variety of genes, showing the huge genetic plasticity of these small replicons. Finally, we also used a metagenomic approach in order to validate this technique, performing this PCR system using total DNA extractions from fecal samples from poultry, turkeys, pigs and humans. Using Illumina sequencing of the PCR products we identified a great diversity of genes encoded by ColE1 replicons, including different antibiotic resistance determinants, supporting the previous results achieved with the collections of bacterial isolates. In addition, we detected cryptic ColE1 plasmids in both families with no known genes in their variable region, which we have named sentinel plasmids. In conclusion, in this work we present a useful genetic tool for the detection and analysis of ColE1 plasmids, and confirm their important role in the dissemination of antibiotic resistance, especially in the Pasteurellaceae family of bacteria.201829615998
996870.9998Antibiotic Resistance, Core-Genome and Protein Expression in IncHI1 Plasmids in Salmonella Typhimurium. Conjugative plasmids from the IncHI1 incompatibility group play an important role in transferring antibiotic resistance in Salmonella Typhimurium. However, knowledge of their genome structure or gene expression is limited. In this study, we determined the complete nucleotide sequences of four IncHI1 plasmids transferring resistance to antibiotics by two different next generation sequencing protocols and protein expression by mass spectrometry. Sequence data including additional 11 IncHI1 plasmids from GenBank were used for the definition of the IncHI1 plasmid core-genome and pan-genome. The core-genome consisted of approximately 123 kbp and 122 genes while the total pan-genome represented approximately 600 kbp. When the core-genome sequences were used for multiple alignments, the 15 tested IncHI1 plasmids were separated into two main lineages. GC content in core-genome genes was around 46% and 50% in accessory genome genes. A multidrug resistance region present in all 4 sequenced plasmids extended over 20 kbp and, except for tet(B), the genes responsible for antibiotic resistance were those with the highest GC content. IncHI1 plasmids therefore represent replicons that evolved in low GC content bacteria. From their original host, they spread to Salmonella and during this spread these plasmids acquired multiple accessory genes including those coding for antibiotic resistance. Antibiotic-resistance genes belonged to genes with the highest level of expression and were constitutively expressed even in the absence of antibiotics. This is the likely mechanism that facilitates host cell survival when antibiotics suddenly emerge in the environment.201627189997
452380.9998Mosaic structure of a multiple-drug-resistant, conjugative plasmid from Campylobacter jejuni. Partial sequence analysis of a tet(O) plasmid from a multiple-drug-resistant clinical isolate of Campylobacter jejuni revealed 10 genes or pseudogenes encoding different aminoglycoside inactivating enzymes, transposase-like genes, and multiple unknown genes from a variety of pathogenic and commensal bacteria. The plasmid could be mobilized by a P incompatibility group plasmid into Escherichia coli, where it apparently integrated into the chromosome and expressed high-level resistance to multiple aminoglycoside antibiotics. This work provides new information about both the nature of drug resistance in C. jejuni and the ability of C. jejuni to exchange genes with other bacterial species.200515917546
996790.9998The biology of IncI2 plasmids shown by whole-plasmid multi-locus sequence typing. IncI2 type plasmids are medium-sized (~55-80 kb) conjugative plasmids that have been found carrying important antimicrobial resistance genes but have also been frequently found as cryptic plasmids. The DNA sequences for 147 fully sequenced IncI2 plasmids were studied by a whole-plasmid multi-locus sequence typing (wpMLST) scheme. A total of 171 loci were identified of which 52 were considered core (carried by greater than 95% of the plasmids). Most of the plasmids carrying the antimicrobial gene mcr-1 were in a distinct clade while most of the antimicrobial gene free plasmids were more distantly related. However, the host strains of bacteria were disparate for both groups of plasmids, showing that conjugal transfer of IncI2 plasmid is frequent. The mcr-1 gene was likely to have been introduced into IncI2 plasmids multiple times. It was also observed that the genes for conjugation showed significant linkage disequilibrium despite substantial diversity for most of those genes. Genes associated with biofilm formation were also among the core genes. The core genes can be considered the cohesive unit that defines the IncI2 plasmid group. Given the role conjugation can play in biofilm formation, it was concluded that conjugation is an active survival strategy for IncI2 plasmids. The IncI2 plasmid will have selective advantage when the plasmid-bearing bacteria are introduced to a new animal host that carries potential conjugal mates.201931629716
4464100.9998Class 1 integrons, gene cassettes, mobility, and epidemiology. Integrons are genetic elements that, although unable to move themselves, contain gene cassettes that can be mobilized to other integrons or to secondary sites in the bacterial genome. The majority of approximately 60 known gene cassettes encode resistance to antibiotics. Recently, a number of gene cassettes encoding extended-spectrum beta-lactamases or carbapenemases have been described. Up to at least five cassettes may be present in an integron, which leads to multiresistance. Frequently, more than one integron is observed within the same bacterial cell. Integrons are widespread in their species distribution. Although integrons are normally reported from Enterobacteriaceae and other gram-negative bacteria, an integron has been described in Corynebacterium glutamicum, a gram-positive species. The gene cassette in this integron showed even higher expression when compared to the expression in Escherichia coli. Integrons have been reported from all continents and are found frequently. The widespread occurrence of integrons is thought to be due to their association with transposon plasmids, conjugative plasmids, or both. Integrons form an important source for the spread of antibiotic resistance, at least in gram-negative bacteria but also potentially in gram-positive bacteria. The aim of this review is to describe the versatility of integrons, especially their mobility and their ability to collect resistance genes.199910614949
1771110.9998Occurrence of integron-associated resistance gene cassettes located on antibiotic resistance plasmids isolated from a wastewater treatment plant. The role of a municipal wastewater treatment plant as a reservoir for bacteria carrying antibiotic resistance plasmids was analysed. Altogether, ninety-seven different multiresistance plasmids were isolated and screened by PCR for the presence of class 1 integron-specific sequences. Twelve of these plasmids were identified to carry integrons. In addition, integron-specific sequences were found on plasmid-DNA preparations from bacteria residing in activated sludge and in the final effluents of the wastewater treatment plant. Sequencing and annotation of the integrons identified nineteen different gene cassette arrays, containing twenty-one different resistance gene cassettes. These cassettes carry genes encoding eight different aminoglycoside-modifying enzymes, seven dihydrofolate reductases, three beta-lactamases, two chloramphenicol resistance proteins and two small exporter proteins. Moreover, new gene cassettes and cassettes with unknown function were identified. Eleven gene cassette combinations are described for the first time. Six integron-associated gene cassette arrays are located on self-transmissible, putative broad-host-range plasmids belonging to the IncP group. Hybridisation analyses, using the integron-specific gene cassette arrays as templates and labelled plasmid-DNA preparations from bacteria of the final effluents as hybridisation probes, revealed that bacteria containing integron-specific sequences on plasmids are released into the environment.200319719593
9889120.9997Evolution and dissemination of L and M plasmid lineages carrying antibiotic resistance genes in diverse Gram-negative bacteria. Conjugative, broad host-range plasmids of the L/M complex have been associated with antibiotic resistance since the 1970s. They are found in Gram-negative bacterial genera that cause human infections and persist in hospital environments. It is crucial that these plasmids are typed accurately so that their clinical and global dissemination can be traced in epidemiological studies. The L/M complex has previously been divided into L, M1 and M2 subtypes. However, those types do not encompass all diversity seen in the group. Here, we have examined 148 complete L/M plasmid sequences in order to understand the diversity of the complex and trace the evolution of distinct lineages. The backbone sequence of each plasmid was determined by removing translocatable genetic elements and reversing their effects in silico. The sequence identities of replication regions and complete backbones were then considered for typing. This supported the distinction of L and M plasmids and revealed that there are five L and eight M types, where each type is comprised of further sub-lineages that are distinguished by variation in their backbone and translocatable element content. Regions containing antibiotic resistance genes in L and M sub-lineages have often formed by initial rare insertion events, followed by insertion of other translocatable elements within the inceptive element. As such, islands evolve in situ to contain genes conferring resistance to multiple antibiotics. In some cases, different plasmid sub-lineages have acquired the same or related resistance genes independently. This highlights the importance of these plasmids in acting as vehicles for the dissemination of emerging resistance genes. Materials are provided here for typing plasmids of the L/M complex from complete sequences or draft genomes. This should enable rapid identification of novel types and facilitate tracking the evolution of existing lineages.202132781088
4466130.9997Antibiotic resistance in gram-negative bacteria: the role of gene cassettes and integrons. Resistance of gram-negative organisms to antibiotics such as beta-lactams, aminoglycosides, trimethoprim and chloramphenicol is caused by many different acquired genes, and a substantial proportion of these are part of small mobile elements known as gene cassettes. A gene cassette consists of the gene and a downstream sequence, known as a 59-base element (59-be), that acts as a specific recombination site. Gene cassettes can move into or out of a specific receptor site (attl site) in a companion element called an integron, and integration or excision of the cassettes is catalysed by a site-specific recombinase (Intl) that is encoded by the integron. At present count there are 40 different cassette-associated resistance genes and three distinct classes of integron, each encoding a distinct Intl integrase. The same cassettes are found in all three classes of integron, indicating that cassettes can move freely between different integrons. Integrons belonging to class I often contain a further antibiotic resistance gene, sull, conferring resistance to sulphonamides. The sull gene is found in a conserved region (3'-CS) that is not present in all members of this class. Class I integrons of the sull type are most prevalent in clinical isolates and have been found in many different organisms. Even though most of them are defective transposon derivatives, having lost at least one of the transposition genes, they are none the less translocatable and consequently found in many different locations. The transposon Tn7 is the best known representative of class 2 integrons, and Tn7 and relatives are also found in many different species.199816904397
9960140.9997Integrons, transposons and IS elements promote diversification of multidrug resistance plasmids and adaptation of their hosts to antibiotic pollutants from pharmaceutical companies. Plasmids are important vehicles for the dissemination of antibiotic resistance genes (ARGs) among bacteria by conjugation. Here, we determined the complete nucleotide sequences of nine different plasmids previously obtained by exogenous plasmid isolation from river and creek sediments and wastewater from a pharmaceutical company. We identified six IncP/P-1ε plasmids and single members of IncL, IncN and IncFII-like plasmids. Genetic structures of the accessory regions of the IncP/P-1ε plasmids obtained implied that multiple insertions and deletions had occurred, mediated by different transposons and Class 1 integrons with various ARGs. Our study provides compelling evidence that Class 1 integrons, Tn402-like transposons, Tn3-like transposons and/or IS26 played important roles in the acquisition of ARGs across all investigated plasmids. Our plasmid sequencing data provide new insights into how these mobile genetic elements could mediate the acquisition and spread of ARGs in environmental bacteria.202337655671
9963150.9997Hitherto-Unnoticed Self-Transmissible Plasmids Widely Distributed among Different Environments in Japan. Various conjugative plasmids were obtained by exogenous plasmid capture, biparental mating, and/or triparental mating methods from different environmental samples in Japan. Based on phylogenetic analyses of their whole-nucleotide sequences, new IncP/P-1 plasmids that could be classified into novel subgroups were obtained. Mini-replicons of the plasmids were constructed, and each of them was incompatible with at least one of the IncP/P-1 plasmids, although they showed diverse iteron sequences in their oriV regions. There were two large clades of IncP/P-1 plasmids, clade I and II. Plasmids in clade I and II included antibiotic resistance genes. Notably, nucleotide compositions of newly found plasmids exhibited different tendencies compared with those of the previously well-studied IncP/P-1 plasmids. Indeed, the host range of plasmids of clade II was different from that of clade I. Although few PromA plasmids have been reported, the number of plasmids belonging to PromAβ, and -γ subgroups detected in this study was close to that of IncP/P-1 plasmids. The host ranges of PromAγ and PromAδ plasmids were broad and transferred to different and distinct classes of Proteobacteria. Interestingly, PromA plasmids and many IncP/P-1 plasmids do not carry any accessory genes. These findings indicate the presence of "hitherto-unnoticed" conjugative plasmids, including IncP/P-1 or PromA derivative ones in nature. These plasmids would have important roles in the exchange of various genes, including antibiotic resistance genes, among different bacteria in nature. IMPORTANCE Plasmids are known to spread among different bacteria. However, which plasmids spread among environmental samples and in which environments they are present is still poorly understood. This study showed that unidentified conjugative plasmids were present in various environments. Different novel IncP/P-1 plasmids were found, whose host ranges were different from those of known plasmids, showing wide diversity of IncP/P-1 plasmids. PromA plasmids, exhibiting a broad host range, were diversified into several subgroups and widely distributed in varied environments. These findings are important for understanding how bacteria naturally exchange their genes, including antibiotic resistance genes, a growing threat to human health worldwide.202236069618
9972160.9997Extensive antimicrobial resistance mobilization via multicopy plasmid encapsidation mediated by temperate phages. OBJECTIVES: To investigate the relevance of multicopy plasmids in antimicrobial resistance and assess their mobilization mediated by phage particles. METHODS: Several databases with complete sequences of plasmids and annotated genes were analysed. The 16S methyltransferase gene armA conferring high-level aminoglycoside resistance was used as a marker in eight different plasmids, from different incompatibility groups, and with differing sizes and plasmid copy numbers. All plasmids were transformed into Escherichia coli bearing one of four different lysogenic phages. Upon induction, encapsidation of armA in phage particles was evaluated using qRT-PCR and Southern blotting. RESULTS: Multicopy plasmids carry a vast set of emerging clinically important antimicrobial resistance genes. However, 60% of these plasmids do not bear mobility (MOB) genes. When carried on these multicopy plasmids, mobilization of a marker gene armA into phage capsids was up to 10000 times more frequent than when it was encoded by a large plasmid with a low copy number. CONCLUSIONS: Multicopy plasmids and phages, two major mobile genetic elements (MGE) in bacteria, represent a novel high-efficiency transmission route of antimicrobial resistance genes that deserves further investigation.202032719862
4531170.9997Various pAQU plasmids possibly contribute to disseminate tetracycline resistance gene tet(M) among marine bacterial community. Emergence of antibiotic-resistant bacteria in the aquaculture environment is a significant problem for disease control of cultured fish as well as in human public health. Conjugative mobile genetic elements (MGEs) are involved in dissemination of antibiotic resistance genes (ARGs) among marine bacteria. In the present study, we first designed a PCR targeting traI gene encoding essential relaxase for conjugation. By this new PCR, we demonstrated that five of 83 strains isolated from a coastal aquaculture site had traI-positive MGEs. While one of the five strains that belonged to Shewanella sp. was shown to have an integrative conjugative element of the SXT/R391 family (ICEVchMex-like), the MGEs of the other four strains of Vibrio spp. were shown to have the backbone structure similar to that of previously described in pAQU1. The backbone structure shared by the pAQU1-like plasmids in the four strains corresponded to a ~100-kbp highly conserved region required for replication, partition and conjugative transfer, suggesting that these plasmids constituted "pAQU group." The pAQU group plasmids were shown to be capable of conjugative transfer of tet(M) and other ARGs from the Vibrio strains to E. coli. The pAQU group plasmid in one of the examined strains was designated as pAQU2, and its complete nucleotide sequence was determined and compared with that of pAQU1. The results revealed that pAQU2 contained fewer ARGs than pAQU1 did, and most of the ARGs in both of these plasmids were located in the similar region where multiple transposases were found, suggesting that the ARGs were introduced by several events of DNA transposition into an ancestral plasmid followed by drug selection in the aquaculture site. The results of the present study indicate that the "pAQU group" plasmids may play an important role in dissemination of ARGs in the marine environment.201424860553
4949180.9997Plasmids of the same Inc groups in Enterobacteria before and after the medical use of antibiotics. Conjugative plasmids were common in enterobacteria isolated before the medical use of antibiotics. Plasmid F of Escherichia coli K-12 was one example and we identified others in over 20% of a collection of strains isolated between 1917 and 1954, the Murray collection. In the past 25 years, conjugative plasmids encoding antibiotic resistances have become common in bacteria of the same genera as those of the Murray Collection--Salmonella, Shigella, Klebsiella, Proteus, Escherichia. The present study was made to show whether the 'pre-antibiotic' plasmids belonged to the same groups, as defined by incompatibility tests (Inc groups), as modern R plasmids. Of 84 such plasmids established in E. coli K-12, none with antibiotic resistance determinants, 65 belonged to the same groups as present resistance (R) plasmids. Thus the remarkable way in which medically important bacteria have acquired antibiotic resistance in the past 25 years seems to have been by the insertion of new genes into existing plasmids rather than by the spread of previously rare plasmids.19836316165
4955190.9997Evidence of extensive interspecies transfer of integron-mediated antimicrobial resistance genes among multidrug-resistant Enterobacteriaceae in a clinical setting. Multidrug resistance in gram-negative bacteria appears to be primarily the result of the acquisition of resistance genes by horizontal transfer. To what extent horizontal transfer may be responsible for the emergence of multidrug resistance in a clinical setting, however, has rarely been investigated. Therefore, the integron contents of isolates collected during a nosocomial outbreak of genotypically unrelated multidrug-resistant Enterobacteriaceae were characterized. The integron was chosen as a marker of transfer because of its association with multiresistance. Some genotypically identical isolates harbored different integrons. Grouping patients carrying the same integron yielded 6 epidemiologically linked clusters, with each cluster representing a different integron. Several patients carried multiple species harboring the same integron. Conjugation experiments with these strains resulted in the transfer of complete resistance patterns at high frequencies (10(-2) to 10(-4)). These findings provide strong evidence that the horizontal transfer of resistance genes contributed largely to the emergence of multidrug-resistant Enterobacteriaceae in this clinical setting.200212089661