# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 414 | 0 | 1.0000 | A plasmid-encoded papB paralogue modulates autoaggregation of Escherichia coli transconjugants. OBJECTIVE: Plasmids are key to antimicrobial resistance transmission among enteric bacteria. It is becoming increasingly clear that resistance genes alone do not account for the selective advantage of plasmids and bacterial strains that harbor them. Deletion of a 32 Kb fitness-conferring region of pMB2, a conjugative resistance plasmid, produced a hyper-autoaggregation phenotype in laboratory Escherichia coli. This study sought to determine the genetic basis for hyper-autoaggregation conferred by the pMB2-derived mini-plasmid. RESULTS: The 32 Kb fragment deleted from pMB2 included previously characterized nutrient acquisition genes as well as putative transposase and integrase genes, a 272 bp papB/ pefB-like gene, and several open-reading frames of unknown function. We cloned the papB/ pefB paralogue and found it sufficient to temper the hyper-autoaggregation phenotype. Hyper-autoaggregation conferred by the mini-plasmid did not occur in a fim-negative background. This study has identified and characterized a gene capable of down-regulating host adhesins and has shown that trans-acting papB/pefB paralogues can occur outside the context of an adhesin cluster. This plasmid-mediated modification of a bacterial host's colonization program may optimize horizontal transfer of the mobile element bearing the genes. | 2020 | 33317611 |
| 426 | 1 | 0.9993 | Plasmid-determined resistance to serum bactericidal activity: a major outer membrane protein, the traT gene product, is responsible for plasmid-specified serum resistance in Escherichia coli. Resistance to the bactericidal activity of serum appears to be an important virulence property of invasive bacteria. The conjugative multiple-antibiotic-resistance plasmid R6-5 was found to confer upon Escherichia coli host bacteria increased resistance against rabbit serum. Gene-cloning techniques were used to localize the serum resistance determinant of R6-5 to a segment of the plasmid that encodes conjugal transfer functions, and a pACYC184 hybrid plasmid, designated pKT107, that contains this segment was constructed. The generation and analysis of deletion and insertion mutant derivatives of the pKT107 plasmid that no longer specify serum resistance permitted precise localization of the serum-resistance cistron on the R6-5 map and demonstrated that this locus is coincident with that of traT, one of the two surface exclusion genes of R6-5. Examination of the proteins synthesized in E. coli minicells of pKT107 and its serum-sensitive mutant derivative plasmids confirmed that the serum-resistance gene product of R6-5 is the traT protein and showed that this protein is a major structural component (about 21,000 copies per cell) of the bacterial outer membrane. | 1980 | 6995306 |
| 429 | 2 | 0.9993 | An integrative vector exploiting the transposition properties of Tn1545 for insertional mutagenesis and cloning of genes from gram-positive bacteria. We have constructed and used an integrative vector, pAT112, that takes advantage of the transposition properties (integration and excision) of transposon Tn1545. This 4.9-kb plasmid is composed of: (i) the replication origin of pACYC184; (ii) the attachment site (att) of Tn1545; (iii) erythromycin-and kanamycin-resistance-encoding genes for selection in Gram- and Gram+ bacteria; and (iv) the transfer origin of IncP plasmid RK2, which allows mobilization of the vector from Escherichia coli to various Gram+ recipients. Integration of pAT112 requires the presence of the transposon-encoded integrase, Int-Tn, in the new host. This vector retains the insertion specificity of the parental element Tn1545 and utilises it to carry out insertional mutagenesis, as evaluated in Enterococcus faecalis. Since pAT112 contains the pACYC184 replicon and lacks most of the restriction sites that are commonly used for molecular cloning, a gene from a Gram+ bacterium disrupted with this vector can be recovered in E. coli by cleavage of genomic DNA, intramolecular ligation and transformation. Regeneration of the gene, by excision of pAT112, can be obtained in an E. coli strain expressing the excisionase and integrase of Tn1545. The functionality of this system was illustrated by characterization of an IS30-like structure in the chromosome of En. faecalis. Derivatives pAT113 and pAT114 contain ten unique cloning sites that allow screening of recombinants having DNA inserts by alpha-complementation in E. coli carrying the delta M15 deletion of lacZ alpha. These vectors are useful to clone and introduce foreign genes into the genomes of Gram+ bacteria. | 1991 | 1657722 |
| 379 | 3 | 0.9993 | Broad host range DNA cloning system for gram-negative bacteria: construction of a gene bank of Rhizobium meliloti. A broad host range cloning vehicle that can be mobilized at high frequency into Gram-negative bacteria has been constructed from the naturally occurring antibiotic resistance plasmid RK2. The vehicle is 20 kilobase pairs in size, encodes tetracycline resistance, and contains two single restriction enzyme sites suitable for cloning. Mobilization is effected by a helper plasmid consisting of the RK2 transfer genes linked to a ColE1 replicon. By use of this plasmid vehicle, a gene bank of the DNA from a wild-type strain of Rhizobium meliloti has been constructed and established in Escherichia coli. One of the hybrid plasmids in the bank contains a DNA insert of approximately 26 kilobase pairs which has homology to the nitrogenase structural gene region of Klebsiella pneumoniae. | 1980 | 7012838 |
| 427 | 4 | 0.9992 | Vesicle-mediated transfer of virulence genes from Escherichia coli O157:H7 to other enteric bacteria. Membrane vesicles are released from the surfaces of many gram-negative bacteria during growth. Vesicles consist of proteins, lipopolysaccharide, phospholipids, RNA, and DNA. Results of the present study demonstrate that membrane vesicles isolated from the food-borne pathogen Escherichia coli O157:H7 facilitate the transfer of genes, which are then expressed by recipient Salmonella enterica serovar Enteritidis or E. coli JM109. Electron micrographs of purified DNA from E. coli O157:H7 vesicles showed large rosette-like structures, linear DNA fragments, and small open-circle plasmids. PCR analysis of vesicle DNA demonstrated the presence of specific genes from host and recombinant plasmids (hly, L7095, mobA, and gfp), chromosomal DNA (uidA and eaeA), and phage DNA (stx1 and stx2). The results of PCR and the Vero cell assay demonstrate that genetic material, including virulence genes, is transferred to recipient bacteria and subsequently expressed. The cytotoxicity of the transformed enteric bacteria was sixfold higher than that of the parent isolate (E. coli JM109). Utilization of the nonhost plasmid (pGFP) permitted the evaluation of transformation efficiency (ca. 10(3) transformants microg of DNA(-1)) and demonstrated that vesicles can deliver antibiotic resistance. Transformed E. coli JM109 cells were resistant to ampicillin and fluoresced a brilliant green. The role vesicles play in genetic exchange between different species in the environment or host has yet to be defined. | 2000 | 11010892 |
| 9823 | 5 | 0.9991 | Transposition of an antibiotic resistance element in mycobacteria. Bacterial resistance to antibiotics is often plasmid-mediated and the associated resistance genes encoded by transposable elements. Mycobacteria, including the human pathogens Mycobacterium tuberculosis and M. leprae, are resistant to many antibiotics, and their cell-surface structure is believed to be largely responsible for the wide range of resistance phenotypes. Antibiotic-resistance plasmids have so far not been implicated in resistance of mycobacteria to antibiotics. Nevertheless, antibiotic-modifying activities such as aminoglycoside acetyltransferases and phosphotransferases have been detected in fast-growing species. beta-lactamases have also been found in most fast- and slow-growing mycobacteria. To date no mycobacterial antibiotic-resistance genes have been isolated and characterized. We now report the isolation, cloning and sequencing of a genetic region responsible for resistance to sulphonamides in M. fortuitum. This region also contains an open reading frame homologous to one present in Tn1696 (member of the Tn21 family) which encodes a site-specific integrase. The mycobacterial resistance element is flanked by repeated sequences of 880 base pairs similar to the insertion elements of the IS6 family found in Gram+ and Gram- bacteria. The insertion element is shown to transpose to different sites in the chromosome of a related fast-growing species, M. smegmatis. The characterization of this element should permit transposon mutagenesis in the analysis of mycobacterial virulence and related problems. | 1990 | 2163027 |
| 263 | 6 | 0.9991 | Selection and characterization of a promoter for expression of single-copy recombinant genes in Gram-positive bacteria. BACKGROUND: In the past ten years there has been a growing interest in engineering Gram-positive bacteria for biotechnological applications, including vaccine delivery and production of recombinant proteins. Usually, bacteria are manipulated using plasmid expression vectors. The major limitation of this approach is due to the fact that recombinant plasmids are often lost from the bacterial culture upon removal of antibiotic selection. We have developed a genetic system based on suicide vectors on conjugative transposons allowing stable integration of recombinant DNA into the chromosome of transformable and non-transformable Gram-positive bacteria. RESULTS: The aim of this work was to select a strong chromosomal promoter from Streptococcus gordonii to improve this genetic system making it suitable for expression of single-copy recombinant genes. To achieve this task, a promoterless gene encoding a chloramphenicol acetyltransferase (cat), was randomly integrated into the S. gordonii chromosome and transformants were selected for chloramphenicol resistance. Three out of eighteen chloramphenicol resistant transformants selected exhibited 100% stability of the phenotype and only one of them, GP215, carried the cat gene integrated as a single copy. A DNA fragment of 600 base pairs exhibiting promoter activity was isolated from GP215 and sequenced. The 5' end of its corresponding mRNA was determined by primer extention analysis and the putative -10 and a -35 regions were identified. To study the possibility of using this promoter (PP) for single copy heterologous gene expression, we created transcriptional fusions of PP with genes encoding surface recombinant proteins in a vector capable of integrating into the conjugative transposon Tn916. Surface recombinant proteins whose expression was controlled by the PP promoter were detected in Tn916-containing strains of S. gordonii and Bacillus subtilis after single copy chromosomal integration of the recombinant insertion vectors into the resident Tn916. The surface recombinant protein synthesized under the control of PP was also detected in Enterococcus faecalis after conjugal transfer of a recombinant Tn916 containing the transcriptional fusion. CONCLUSION: We isolated and characterized a S. gordonii chromosomal promoter. We demonstrated that this promoter can be used to direct expression of heterologous genes in different Gram-positive bacteria, when integrated in a single copy into the chromosome. | 2005 | 15651989 |
| 428 | 7 | 0.9991 | Identification and analysis of genes for tetracycline resistance and replication functions in the broad-host-range plasmid pLS1. The streptococcal plasmid pMV158 and its derivative pLS1 are able to replicate and confer tetracycline resistance in both Gram-positive and Gram-negative bacteria. Copy numbers of pLS1 were 24, 4 and 4 molecules per genome in Streptococcus pneumoniae, Bacillus subtilis and Escherichia coli, respectively. Replication of the streptococcal plasmids in E. coli required functional polA and recA genes. A copy-number mutation corresponding to a 332 base-pair deletion of pLS1 doubled the plasmid copy number in all three species. Determination of the complete DNA sequence of pLS1 revealed transcriptional and translational signals and four open reading frames. A putative inhibitory RNA was encoded in the region deleted by the copy-control mutation. Two putative mRNA transcripts encoded proteins for replication functions and tetracycline resistance, respectively. The repB gene encoded a trans-acting, 23,000 Mr protein necessary for replication, and the tet gene encoded a very hydrophobic, 50,000 Mr protein required for tetracycline resistance. The polypeptides corresponding to these proteins were identified by specific labeling of plasmid-encoded products. The tet gene of pLS1 was highly homologous to tet genes in two other plasmids of Gram-positive origin but different in both sequence and mode of regulation from tet genes of Gram-negative origin. | 1986 | 2438417 |
| 9303 | 8 | 0.9991 | A Conserved Class II Type Thioester Domain-Containing Adhesin Is Required for Efficient Conjugation in Bacillus subtilis. Conjugation, the process by which a DNA element is transferred from a donor to a recipient cell, is the main horizontal gene transfer route responsible for the spread of antibiotic resistance and virulence genes. Contact between a donor and a recipient cell is a prerequisite for conjugation, because conjugative DNA is transferred into the recipient via a channel connecting the two cells. Conjugative elements encode proteins dedicated to facilitating the recognition and attachment to recipient cells, also known as mating pair formation. A subgroup of the conjugative elements is able to mediate efficient conjugation during planktonic growth, and mechanisms facilitating mating pair formation will be particularly important in these cases. Conjugative elements of Gram-negative bacteria encode conjugative pili, also known as sex pili, some of which are retractile. Far less is known about mechanisms that promote mating pair formation in Gram-positive bacteria. The conjugative plasmid pLS20 of the Gram-positive bacterium Bacillus subtilis allows efficient conjugation in liquid medium. Here, we report the identification of an adhesin gene in the pLS20 conjugation operon. The N-terminal region of the adhesin contains a class II type thioester domain (TED) that is essential for efficient conjugation, particularly in liquid medium. We show that TED-containing adhesins are widely conserved in Gram-positive bacteria, including pathogens where they often play crucial roles in pathogenesis. Our study is the first to demonstrate the involvement of a class II type TED-containing adhesin in conjugation.IMPORTANCE Bacterial resistance to antibiotics has become a serious health care problem. The spread of antibiotic resistance genes between bacteria of the same or different species is often mediated by a process named conjugation, where a donor cell transfers DNA to a recipient cell through a connecting channel. The first step in conjugation is recognition and attachment of the donor to a recipient cell. Little is known about this first step, particularly in Gram-positive bacteria. Here, we show that the conjugative plasmid pLS20 of Bacillus subtilis encodes an adhesin protein that is essential for effective conjugation. This adhesin protein has a structural organization similar to adhesins produced by other Gram-positive bacteria, including major pathogens, where the adhesins serve in attachment to host tissues during colonization and infection. Our findings may thus also open novel avenues to design drugs that inhibit the spread of antibiotic resistance by blocking the first recipient-attachment step in conjugation. | 2021 | 33727345 |
| 451 | 9 | 0.9991 | Functional Analysis of the Acinetobacter baumannii XerC and XerD Site-Specific Recombinases: Potential Role in Dissemination of Resistance Genes. Modules composed of a resistance gene flanked by Xer site-specific recombination sites, the vast majority of which were found in Acinetobacter baumannii, are thought to behave as elements that facilitate horizontal dissemination. The A. baumannii xerC and xerD genes were cloned, and the recombinant clones used to complement the cognate Escherichia coli mutants. The complemented strains supported the resolution of plasmid dimers, and, as is the case with E. coli and Klebsiella pneumoniae plasmids, the activity was enhanced when the cells were grown in a low osmolarity growth medium. Binding experiments showed that the partially purified A. baumannii XerC and XerD proteins (XerC(Ab) and XerD(Ab)) bound synthetic Xer site-specific recombination sites, some of them with a nucleotide sequence deduced from existing A. baumannii plasmids. Incubation with suicide substrates resulted in the covalent attachment of DNA to a recombinase, probably XerC(Ab), indicating that the first step in the recombination reaction took place. The results described show that XerC(Ab) and XerD(Ab) are functional proteins and support the hypothesis that they participate in horizontal dissemination of resistant genes among bacteria. | 2020 | 32668667 |
| 4494 | 10 | 0.9991 | A mobile restriction modification system consisting of methylases on the IncA/C plasmid. BACKGROUND: IncA/C plasmids play important roles in the development and dissemination of multidrug resistance in bacteria. These plasmids carry three methylase genes, two of which show cytosine specificity. The effects of such a plasmid on the host methylome were observed by single-molecule, real-time (SMRT) and bisulfite sequencing in this work. RESULTS: The results showed that the numbers of methylation sites on the host chromosomes were changed, as were the sequences recognized by MTase. The host chromosomes were completely remodified by the plasmid with a methylation pattern different from that of the host itself. When the three dcm genes were deleted, the transferability of the plasmid into other Vibrio cholerae and Escherichia coli strains was lost. During deletion of the dcm genes, except for the wild-type strains and the targeted deletion strains, 18.7%~ 38.5% of the clones lost the IncA/C plasmid and changed from erythromycin-, azithromycin- and tetracycline-resistant strains to strains that were sensitive to these antibiotics. CONCLUSIONS: Methylation of the IncA/C plasmid was a new mobile restriction modification (RM) barrier against foreign DNA. By actively changing the host's methylation pattern, the plasmid crossed the barrier of the host's RM system, and this might be the simplest and most universal method by which plasmids acquire a broad host range. Elimination of plasmids by destruction of plasmid stability could be a new effective strategy to address bacterial multidrug resistance. | 2019 | 31182978 |
| 9822 | 11 | 0.9990 | Molecular mechanisms for transposition of drug-resistance genes and other movable genetic elements. Transposition is proposed to be responsible for the rapid evolution of multiply drug-resistant bacterial strains. Transposons, which carry the genes encoding drug resistance, are linear pieces of DNA that range in size from 2.5 to 23 kilobase pairs and always contain at their ends nucleotide sequences repeated in inverse order. In some transposons the terminal inverted repeat sequences are capable of independent movement and are called insertion sequences. Transposons carry a gene that encodes transposase(s), the enzyme(s) responsible for recombination of the transposon into another DNA molecule. Studies on transposable genetic elements in bacteria have not only given insight into the spread of antibiotic resistance but also into the process of DNA movement. | 1987 | 3035697 |
| 6324 | 12 | 0.9990 | Genetic and biochemical basis of tetracycline resistance. Properties of several, well characterized, tetracycline resistance determinants were compared. The determinants in Tn1721 and Tn10 (both from Gram-negative bacteria) each contain two genes; one encodes a repressor that regulates both its own transcription and that of a membrane protein that confers resistance by promoting efflux of the drug. Determinants from Gram-positive bacteria also encode efflux proteins, but expression of resistance is probably regulated by translational attenuation. The likely tetracycline binding site (a common dipeptide) in each efflux protein was predicted. The presence of the common binding site is consistent with the ability of an efflux protein originating in Bacillus species to be expressed in Escherichia coli. | 1986 | 3542941 |
| 409 | 13 | 0.9990 | A Novel Plasmid Entry Exclusion System in pKPC_UVA01, a Promiscuous Conjugative Plasmid Carrying the bla(KPC) Carbapenemase Gene. Conjugative plasmids are the principal mediator in the emergence and spread of antibiotic resistance genes in Enterobacterales. Plasmid entry exclusion (EEX) systems can restrict their transfer into the recipient bacteria carrying closely related plasmids. In this study, we identified and characterized a novel plasmid entry exclusion system in a carbapenem resistance plasmid pKPC_UVA01, which is responsible for widespread dissemination of the bla(KPC) carbapenemase gene among Enterobacterales in the United States. The identified eex gene in the recipient strain of different Enterobacterales species inhibited the conjugation transfer of pKPC_UVA01 plasmids at a range of 200- to 400-fold, and this inhibition was found to be a dose-dependent function of the EEX protein in recipient cells. The C terminus truncated version of eex or eex with an early termination codon at the C terminus region alleviated the inhibition of conjugative transfer. Unlike the strict specificity of plasmid exclusion by the known EEX protein, the newly identified EEX in the recipient strain could inhibit the transfer of IncP and IncN plasmids. The eex gene from the plasmid pKPC_UVA01 was not required for conjugative transfer but was essential in the donor bacteria for entry exclusion of this plasmid. This was a novel function of a single protein that is essential in both donor and recipient bacteria for the entry exclusion of a plasmid. This eex gene is found to be distributed in multidrug resistance plasmids similar to pKPC_UVA01 in different Enterobacterales species and may contribute to the stability of this plasmid type by controlling its transfer. | 2022 | 35007138 |
| 352 | 14 | 0.9990 | Transposon vectors containing non-antibiotic resistance selection markers for cloning and stable chromosomal insertion of foreign genes in gram-negative bacteria. A simple procedure for cloning and stable insertion of foreign genes into the chromosomes of gram-negative eubacteria was developed by combining in two sets of plasmids (i) the transposition features of Tn10 and Tn5; (ii) the resistances to the herbicide bialaphos, to mercuric salts and organomercurial compounds, and to arsenite, and (iii) the suicide delivery properties of the R6K-based plasmid pGP704. The resulting constructions contained unique NotI or SfiI sites internal to either the Tn10 or the Tn5 inverted repeats. These sites were readily used for cloning DNA fragments with the help of two additional specialized cloning plasmids, pUC18Not and pUC18Sfi. The newly derived constructions could be maintained only in donor host strains that produce the R6K-specified pi protein, which is an essential replication protein for R6K and plasmids derived therefrom. Donor plasmids containing hybrid transposons were transformed into a specialized lambda pir lysogenic Escherichia coli strain with a chromosomally integrated RP4 that provided broad-host-range conjugal transfer functions. Delivery of the donor plasmids into selected host bacteria was accomplished through mating with the target strain. Transposition of the hybrid transposon from the delivered suicide plasmid to a replicon in the target cell was mediated by the cognate transposase encoded on the plasmid at a site external to the transposon. Since the transposase function was not maintained in target cells, such cells were not immune to further transposition rounds. Multiple insertions in the same strain are therefore only limited by the availability of distinct selection markers. The utility of the system was demonstrated with a kanamycin resistance gene as a model foreign insert into Pseudomonas putida and a melanin gene from Streptomyces antibioticus into Klebsiella pneumoniae. Because of the modular nature of the functional parts of the cloning vectors, they can be easily modified and further selection markers can be incorporated. The cloning system described here will be particularly useful for the construction of hybrid bacteria that stably maintain inserted genes, perhaps in competitive situations (e.g., in open systems and natural environments), and that do not carry antibiotic resistance markers characteristic of most available cloning vectors (as is currently required of live bacterial vaccines). | 1990 | 2172216 |
| 387 | 15 | 0.9990 | Expression of tetracycline resistance in pBR322 derivatives reduces the reproductive fitness of plasmid-containing Escherichia coli. Plasmid pBR322 and its numerous derivatives are used extensively for research and in biotechnology. The tetracycline-resistance (TcR) genes in these plasmids are expressed constitutively and cells carrying these plasmids are resistant to tetracycline. We have shown that expression of the TcR gene has an adverse effect on the reproductive fitness of plasmid-containing bacteria in both glucose-limited batch and chemostat cultures. If the TcR genes are inactivated at any one of three different restriction sites, mixed cultures of plasmid-free and plasmid-containing bacteria grow at the same rate. | 1985 | 3005111 |
| 9298 | 16 | 0.9990 | Delivering "Chromatic Bacteria" Fluorescent Protein Tags to Proteobacteria Using Conjugation. Recently, we published a large and versatile set of plasmids, the chromatic bacteria toolbox, to deliver eight different fluorescent protein genes and four combinations of antibiotic resistance genes to Gram-negative bacteria. Fluorescent tags are important tools for single-cell microbiology, synthetic community studies, biofilm, and host-microbe interaction studies. Using conjugation helper strain E. coli S17-1 as a donor, we show how plasmid conjugation can be used to deliver broad host range plasmids, Tn5 transposons delivery plasmids, and Tn7 transposon delivery plasmids into species belonging to the Proteobacteria. To that end, donor and recipient bacteria are grown under standard growth conditions before they are mixed and incubated under non-selective conditions. Then, transconjugants or exconjugant recipients are selected on selective media. Mutant colonies are screened using a combination of tools to ensure that the desired plasmids or transposons are present and that the colonies are not containing any surviving donors. Through conjugation, a wide range of Gram-negative bacteria can be modified without prior, often time-consuming, establishment of competent cell and electroporation procedures that need to be adjusted for every individual strain. The here presented protocol is not exclusive for the delivery of Chromatic bacteria plasmids and transposons, but can also be used to deliver other mobilizable plasmids to bacterial recipients. | 2019 | 33654996 |
| 290 | 17 | 0.9990 | Utility of the clostridial site-specific recombinase TnpX to clone toxic-product-encoding genes and selectively remove genomic DNA fragments. TnpX is a site-specific recombinase responsible for the excision and insertion of the transposons Tn4451 and Tn4453 in Clostridium perfringens and Clostridium difficile, respectively. Here, we exploit phenotypic features of TnpX to facilitate genetic mutagenesis and complementation studies. Genetic manipulation of bacteria often relies on the use of antibiotic resistance genes; however, a limited number are available for use in the clostridia. The ability of TnpX to recognize and excise specific DNA fragments was exploited here as the basis of an antibiotic resistance marker recycling system, specifically to remove antibiotic resistance genes from plasmids in Escherichia coli and from marked chromosomal C. perfringens mutants. This methodology enabled the construction of a C. perfringens plc virR double mutant by allowing the removal and subsequent reuse of the same resistance gene to construct a second mutation. Genetic complementation can be challenging when the gene of interest encodes a product toxic to E. coli. We show that TnpX represses expression from its own promoter, PattCI, which can be exploited to facilitate the cloning of recalcitrant genes in E. coli for subsequent expression in the heterologous host C. perfringens. Importantly, this technology expands the repertoire of tools available for the genetic manipulation of the clostridia. | 2014 | 24682304 |
| 420 | 18 | 0.9990 | Transferable nitrofuran resistance conferred by R-plasmids in clinical isolates of Escherichia coli. A high proportion of nitrofuran-resistant strains has been found in a collection of antibiotic-resistant Gram-negative bacteria isolated from patients with urinary tract infections. Some of the Escherichia coli carried R-plasmids that conferred resistance to nitrofurantoin and nitrofurazone. The mechanism of resistance is not clear; only in lactose non-fermenting recipients was there a decrease in the nitrofuran-reducing ability of whole-cell suspensions. One of the plasmids conferred enhanced resistance to UV light on DNA repair defective mutants but not on repair efficient strains. In some resistant strains, the total resistance was apparently the result of a combination of chromosomal and plasmid-borne genes. The presence of the plasmid may allow the development of higher resistance levels by mutation of chromosomal genes. | 1983 | 6368515 |
| 9973 | 19 | 0.9990 | Spread 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. | 2018 | 30022749 |