Epidemiological study of sulfonamide and trimethoprim resistance genes in Enterobacteriaceae. - Related Documents




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595001.0000Epidemiological study of sulfonamide and trimethoprim resistance genes in Enterobacteriaceae. Sulfonamide (Su) and trimethoprim (Tp) resistance are known to caused by the production of drug resistant dihydropteroate synthase (DHPS) and dihydrofolate reductase (DHFR), respectively. Sulfonamide and trimethoprim are often used in combination under the name cotrimoxazole. Cotrimoxazole resistance in various enteric bacteria isolated at Ramathibodi Hospital was studied. The rate of resistance from 1984-1989 of many genera was rather constant at 40%-60% except in Shigella spp in which the rate increased rapidly in 1987 till 1989. Seventy-five percent of Su-Tp resistant (Sur-Tpr) bacteria were also found to be resistant to other drugs such as ampicillin, aminoglycosides, tetracycline and chloramphenicol in addition to cotrimoxazole. Two hundred and forty Su-Tp resistant strains were analysed for the presence of type I and II dihydropteroate synthase as well as type I and V dihydrofolate reductase genes by hybridization with the corresponding gene probes. Type I DHPS gene predominated in Su-Tp resistant bacteria at 60.8% whereas type II DHPS was found in only 25%. Some strains (11.7%) had both genotypes but 2.5% did not have any. In the trimethoprim resistance study, the DHFR type I gene was also found more frequently (30%) whereas type V DHFR was only 19%. The remaining of Tp resistance (51%) was unclassified. The coexistence of Su and Tp resistance genes of each type was investigated among 118 Su and Tp resistant strains. It was found that type I DHPS gene was found together with either type I or V DHFR gene and type II DHPS was found with type I DHFR gene at about the same rate (28.9%, 27.1% and 26.3%, respectively). However, the presence of type II DHPS together with type V DHFR was rather low, only 5.9% of isolates were found to have both types of genes.19902237584
592010.9995Study on acquisition of bacterial antibiotic resistance determinants in poultry litter. Antibiotic resistance and the mode of transmission were investigated in bacteria isolated from poultry litter. Total aerobic heterotrophic bacteria were screened and identified for their resistance to different antibiotics such as ampicillin, streptomycin, erythromycin, tetracycline, chloramphenicol, kanamycin, tobramycin, and rifampicin. The distribution of bacteria found in the litter was Staphylococcus (29.1%), which was the predominant group, followed by Streptococcus (25%), Micrococcus (20.8%), Escherichia coli (12.5%), Salmonella (8.3%), and Aeromonas (4.1%). Fifty percent of these isolates were susceptible to ampicillin, 57% to erythromycin, 25% to tetracycline, 4% to chloramphenicol, 40% to kanamycin, 75% to streptomycin, 54% to tobramycin, and 4% to rifampicin. Three randomly selected isolates representing Staphylococcus, Streptococcus, and Micrococcus were examined for plasmids, and plasmid-curing and plasmid-induced transformation studies were conducted. Streptococcus and Micrococcus harbored a plasmid of 4.2 and 5.1 kb, respectively, whereas Staphylococcus did not harbor any plasmids. Plasmids were cured in Streptococcus and Micrococcus at a concentration of 75 and 100 microg/ mL of acridine orange, respectively, and transformation of 4.2- and 5.1-kb plasmids isolated from the Streptococcus and Micrococcus to plasmid-free E. coli DH5alpha strain was possible. In conjugation experiments, the antibiotic resistance profiles of transconjugant cells were found to be the same as the donors with the exception of Staphylococcus. The results of this study suggest that transformation and conjugation could be an important mechanism for horizontal gene transfer between bacteria in poultry litter. An understanding of the mechanism and magnitude of resistance gene transfer may provide a strategy to reduce the potential for dissemination of these genes.200919531707
586220.9995Diversity of tetracycline resistance genes in bacteria from Chilean salmon farms. Twenty-five distinct tetracycline-resistant gram-negative bacteria recovered from four Chilean fish farms with no history of recent antibiotic use were examined for the presence of tetracycline resistance (tet) genes. Sixty percent of the isolates carried 1 of the 22 known tet genes examined. The distribution was as follows. The tet(A) gene was found in six isolates. The tet(B) gene was found in two isolates, including the first description in the genus Brevundimonas: Two isolates carried the tet(34) and tet(B) genes, including the first description of the tet(34) gene in Pseudomonas and Serratia and the first description of the tet(B) gene in Pseudomonas: The tet(H) gene was found in two isolates, which includes the first description in the genera Moraxella and Acinetobacter: One isolate carried tet(E), and one isolate carried tet(35), the first description of the gene in the genus Stenotrophomonas: Finally, one isolate carried tet(L), found for the first time in the genus Morganella: By DNA sequence analysis, the two tet(H) genes were indistinguishable from the previously sequenced tet(H) gene from Tn5706 found in Pasteurella multocida. The Acinetobacter radioresistens isolate also harbored the Tn5706-associated 1,063-bp IS element IS1597, while the Moraxella isolate carried a 1,026-bp IS-like element whose 293-amino-acid transposase protein exhibited 69% identity and 84% similarity to the transposase protein of IS1597, suggesting the presence of a novel IS element. The distribution of tet genes from the Chilean freshwater ponds was different than those that have previously been described from other geographical locations, with 40% of the isolates carrying unidentified tetracycline resistance genes.200312604516
595230.9995Apramycin and gentamicin resistance in Escherichia coli and salmonellas isolated from farm animals. Since the aminoglycoside antibiotic apramycin was licensed for veterinary use in 1980, all isolates of Escherichia coli and salmonellas received at the Central Veterinary Laboratory have been monitored for resistance to apramycin and the related antibiotic gentamicin. During the period 1982-4, the incidence of resistance in E. coli to apramycin increased from 0.6% in 1982 to 2.6% in 1984. In salmonellas the incidence of resistance to apramycin increased from 0.1% in 1982 to 1.4% in 1984. Resistance to both apramycin and gentamicin was detected in six different salmonella serotypes, although an isolate of Salmonella thompson from poultry was resistant to gentamicin but not apramycin. Most of the cultures were isolated from pigs, although the incidence of apramycin resistance in S. typhimurium (DT 204C) from calves has shown a recent dramatic increase. All the isolates with one exception produced the enzyme aminoglycoside 3-N-acetyltransferase IV (ACC(3)IV). The resistance was transferable by conjugation in most of the strains examined, and the plasmids specifying the resistance have been found to belong to a number of different incompatibility groups. Plasmids from three E. coli strains were compatible with all the reference plasmids and belonged to a previously undescribed group which was investigated further. It is suggested that bacteria from humans should be examined for resistance to apramycin and gentamicin to determine the possibility of the antibiotic-resistance bacteria, and their genes, spreading from animals to humans.19863540112
595540.9995Integrons and gene cassettes in clinical isolates of co-trimoxazole-resistant Gram-negative bacteria. Despite a trend of declining consumption, resistance to co-trimoxazole has increased during a 12-year period in Stockholm. The molecular background to this surprising development was investigated by using PCR to screen for integrons and specific resistance genes, followed by sequence analysis of selected integrons, in 105 clinical urinary isolates of Gram-negative bacteria selected partly for trimethoprim resistance. Sixty-five integrons of class 1 or 2 were detected in a subset of 59 isolates, and of these positive isolates, all but one were resistant to trimethoprim. However, 11 isolates were resistant to trimethoprim, but negative for integrons. Isolates positive for integrons were resistant to an average of 4.2 antibiotics, compared with 1.9 antibiotics for integron-negative isolates. Despite this, the only gene cassettes identified in 19 class 1 integrons analysed were dfr and aadA cassettes. Thus, only resistance to trimethoprim, streptomycin, spectinomycin and sulphonamides could be explained by the presence of integrons in these isolates. A new dfr gene, named dfrA22, was discovered as a single gene cassette in a class 1 integron. In addition, sulphonamide resistance in many isolates was caused by carriage of sul2, which has no known association with integrons. Resistance to co-trimoxazole and many other antibiotics was thus not accounted for fully by the presence of integrons in these isolates.200515715715
595450.9995Distribution of genes for trimethoprim and gentamicin resistance in bacteria and their plasmids in a general hospital. The incidence of trimethoprim resistance in enterobacteria causing infection in a London hospital increased from 5.6% in 1970 to 16% in 1979. The proportion of gentamicin-resistant aerobic Gram-negative bacilli had risen to 6.5% by 1979. During a 5-month period in 1977, during which no epidemic was recognized, all isolates resistant to either trimethoprim, gentamicin, tobramycin or amikacin were studied. The proportion of enterobacteria resistant to both trimethoprim and gentamicin (3.8% of the total) was significantly higher than expected assuming no correlation between acquisition of resistance characters. The resistance was transferable in 23% of trimethoprim-resistant and 76% of gentamicin-resistant strains. Trimethoprim resistance was carried by plasmids of seven different incompatibility groups and in at least four instances was part of a transposon. Gentamicin resistance was determined by plasmids of three groups - IncC, IncFII and IncW. Transposition of gentamicin resistance was not shown, though this may have been the means of evolution of the gentamicin R plasmids of InW, which determined aminoglycoside acetyltransferase, AAC(3). Some bacterial strains with their plasmids were endemic. There was evidence for these plasmids (i) acquiring new resistance genes by transposition, (ii) losing resistance genes by deletion and (iii) being transferred between bacterial species in the hospital.19807003059
595360.9995CAT III chloramphenicol resistance in Pasteurella haemolytica and Pasteurella multocida isolated from calves. Chloramphenicol, which had been used extensively for antimicrobial veterinary therapy, was prohibited in Europe in 1994. Soon after it became available, resistance to this drug was detected, generally conferred by plasmids encoding inactivating enzymes, the chloramphenicol acetyltransferases (CAT), in Gram-negative as well as in Gram-positive bacteria. In the last few years, resistance to antibiotics emerged in Pasteurella strains from breeding herds and this evolution was followed by a national surveillance network. Chloramphenicol-resistance was more recently detected in multiresistant strains. We studied 25 strains of Pasteurella, selected for their resistance to chloramphenicol. Production of a CAT was demonstrated in all these strains. PCR amplification indicated that the CAT produced was of type III for 23 of them. In these strains, chloramphenicol-resistance was mediated by plasmids of about 5.1 kb. Southern blots on restriction fragments suggested a high degree of homology between these 5.1 kb plasmids. In the two other strains, production of a CAT type I was demonstrated, and the corresponding genes were either shown on a plasmid of 17 or 5.5 kb.19968877534
595770.9995ant(6)-I Genes Encoding Aminoglycoside O-Nucleotidyltransferases Are Widely Spread Among Streptomycin Resistant Strains of Campylobacter jejuni and Campylobacter coli. Thermotolerant Campylobacter species C. jejuni and C. coli are actually recognized as the major bacterial agent responsible for food-transmitted gastroenteritis. The most effective antimicrobials against Campylobacter are macrolides and some, but not all aminoglycosides. Among these, susceptibility to streptomycin is reduced by mutations in the ribosomal RPSL protein or by expression of ANT(6)-I aminoglycoside O-nucleotidyltransferases. The presence of streptomycin resistance genes was evaluated among streptomycin-resistant Campylobacter isolated from humans and animals by using PCR with degenerated primers devised to distinguish ant(6)-Ia, ant(6)-Ib and other ant-like genes. Genes encoding ANT(6)-I enzymes were found in all possible combinations with a major fraction of the isolates carrying a previously described ant-like gene, distantly related and belonging to the new ant(6)-I sub-family ant(6)-Ie. Among Campylobacter isolates, ant(6)-Ie was uniquely found functional in C. coli, as shown by gene transfer and phenotype expression in Escherichia coli, unlike detected coding sequences in C. jejuni that were truncated by an internal frame shift associated to RPSL mutations in streptomycin resistant strains. The genetic relationships of C. coli isolates with ANT(6)-Ie revealed one cluster of strains presented in bovine and humans, suggesting a circulation pathway of Campylobacter strains by consuming contaminated calf meat by bacteria expressing this streptomycin resistance element.201830405573
593380.9995Novel macrolide-resistance genes, mef(C) and mph(G), carried by plasmids from Vibrio and Photobacterium isolated from sediment and seawater of a coastal aquaculture site. The aim of this study was to determine whether mef(C) and mph(G), originally found on the transferable multi-drug plasmid pAQU1 from Photobacterium damselae subsp. damselae isolated from seawater of a fish farm, are responsible for conferring macrolide resistance. Since these genes are localized head-to-tail on pAQU1 and only four nucleotides exist between them, the single- and combination-effect of these genes was examined. When mph(G) alone was introduced to Escherichia coli, the minimum inhibitory concentrations (MICs) against erythromycin, clarithromycin and azithromycin increased, whereas introduction of mef(C) alone did not influence macrolide susceptibility. Introduction of both mef(C) and mph(G) dramatically increased the MICs to the same three macrolides, i.e. >512 μg ml(-1) , >512 μg ml(-1) and 128 μg ml(-1) respectively. These results suggest that the macrolide phosphotransferase encoded by mph(G) is essential for macrolide resistance, while the efflux pump encoded by mef(C) is required for high-level macrolide resistance. The tandem-pair arrangements of the mef(C) and mph(G) genes were conserved on plasmids ranging in size from 240 to 350 kb of the 22 erythromycin-resistant strains belonging to Vibrio and Photobacterium obtained from the fish farm. Sixteen of 22 plasmids ranged in size from 300 to 350 kb. This is the first report of novel macrolide resistance genes originating from a marine bacterium. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, mef(C) and mph(G) were found to be novel macrolide-resistance genes, and this is the first report of macrolide-resistance genes originating from a marine bacterium. These genes may be responsible for previously reported cases of the emergence of erythromycin-resistant bacteria in aquaculture sites by an unknown mechanism. The introduction of the tandem arrangement of the mef(C) and mph(G) genes in Escherichia coli increased the MICs to erythromycin, clarithromycin and azithromycin, suggesting a novel mechanism conferring high-level macrolide resistance via combined expression of the efflux pump and macrolide phosphotransferase.201525765542
201090.9995Epidemiological survey of genes encoding aminoglycoside phosphotransferases APH (3') I and APH (3') II using DNA probes. The epidemiological survey of APH (3') I and APH (3') II genes, at a time when the specific antibiotic pressure was very low, was carried out by DNA-DNA hybridization. The sample included 334 aminoglycoside resistant Gram-negative bacteria collected from patients of a General Hospital. Of these, 251 hybridized with the APH (3') I-probe and 19 with the APH (3') II-probe but only 190 strains showed high resistance levels (CIM greater than 64 micrograms/ml) for kanamycin, neomycin and paromomycin. These strains were isolated both from inpatients and outpatients with different infectious diseases. The APH (3') I-gene was dispersed among all the bacterial species and clinical specimens tested but the APH (3') II-gene was not found in Pseudomonas spp, Escherichia coli, Citrobacter freundii and Enterobacter cloacae, nor in infected catheters. Several plasmids of different sizes carrying APH (3') genes were detected among different bacteria. Plasmids along with transposable elements (the probes used in this work were developed from Tn906 and Tn5) and the high consumption of other antibiotics whose resistance is carried by these bacteria might be playing an important role in the maintenance and dispersion of APH (3') genes.19921328557
2014100.9994Class 1 and class 2 integrons in multidrug-resistant gram-negative bacteria isolated from the Salmon River, British Columbia. Using an enrichment protocol, we isolated 16 gram-negative, multidrug-resistant strains of known or opportunistic bacterial pathogens from the Salmon River in south-central British Columbia from 2005 to 2009, and investigated the genetic basis of their resistance to a variety of antibiotics. Of the 16 strains, 13 carried class 1 integrons and three carried class 2 integrons. Genes found in cassettes associated with the integrons included those for dihydrofolate reductases (dfrA1, dfrA12, dfrA17, and dfrB7), aminoglycoside adenyltransferases (aadA1, aadA2, aadA5, and aadB), streptothricin acetyltransferase (sat), and hypothetical proteins (orfF and orfC). A new gene cassette of unknown function, orf1, was discovered between dfrA1 and aadA5 in Escherichia sp. Other genes for resistance to tetracycline, chloramphenicol, streptomycin, and kanamycin (tetA, tetB, tetD; catA; strA-strB; and aphA1-Iab, respectively) were outside the integrons. Several of these resistance determinants were transferable by conjugation. The detection of organisms and resistance determinants normally associated with clinical settings attest to their widespread dispersal and suggest that regular monitoring of their presence in aquatic habitats should become a part of the overall effort to understand the epidemiology of antibiotic resistance genes in bacteria.201121627486
5848110.9994Plasmid and chromosomal basis of tolerance to cadmium and resistance to antibiotics in normal bovine duodenal bacterial flora. Cadmium (Cd) tolerance and antibiotic resistance was studied in duodenal flora of 20 normal bovine samples. Twelve bacterial isolates (5 Staphylococcus spp, 4 Enterococcus faecalis, 2 Bacillus spp, and a Pseudomonas sp) were grown in Luria broth containing 0.05 to 0.8 mM of cadmium chloride (CdCl). All isolates displayed multiple antibiotic resistance, with 2 Enterococcus strains and Pseudomonas pickettii demonstrating resistance to 12/17 antibiotics tested. With the exception of Staphylococcus sp, all contained plasmid DNA. Curing to remove plasmid DNA determined if Cd tolerance and/or antibiotic resistance was plasmid or chromosomally mediated. None of the bacteria became sensitive to CdCl after curing, suggesting that tolerance was not plasmid-mediated. Six bacteria became sensitive to antibiotics after curing indicating that antibiotic2 resistance was plasmid mediated. Two of these bacteria became sensitive to multiple antibiotics; a Staphylococcus sp became sensitive to ampicillin, ceftiofur and cephalothin, and a Enterococcus strain became sensitive to neomycin, oxacillin, and tiamulin. All of the isolates were probed for the presence of known Cd-resistance genes (cadA, cadC, and cadD). DNA-DNA hybridization revealed cadA- and cadC-related sequences in chromosomal DNA of a Staphylococcus sp, an Enterococcus strain, and in plasmid DNA of another Staphylococcus sp. No cadD-related sequences were detected in any of the 12 isolates even under reduced stringency of hybridization.200111383651
2906120.9994The mef(A) gene predominates among seven macrolide resistance genes identified in gram-negative strains representing 13 genera, isolated from healthy Portuguese children. Of the 176 randomly selected, commensal, gram-negative bacteria isolated from healthy children with low exposure to antibiotics, 138 (78%) carried one or more of the seven macrolide resistance genes tested in this study. These isolates included 79 (91%) isolates from the oral cavity and 59 (66%) isolates from urine samples. The mef(A) gene, coding for an efflux protein, was found in 73 isolates (41%) and was the most frequently carried gene. The mef(A) gene could be transferred from the donors into a gram-positive E. faecalis recipient and a gram-negative Escherichia coli recipient. The erm(B) gene transferred and was maintained in the E. coli transconjugants but was found in 0 to 100% of the E. faecalis transconjugants tested, while the other five genes could be transferred only into the E. coli recipient. The individual macrolide resistance genes were identified in 3 to 12 new genera. Eight (10%) of the oral isolates and 30 (34%) of the urine isolates for which the MICs were 2 to >500 microg of erythromycin per ml did not hybridize with any of the seven genes and may carry novel macrolide resistance genes.200415328110
5411130.9994Detection of the aminoglycosidestreptothricin resistance gene cluster ant(6)-sat4-aph(3 ')-III in commensal viridans group streptococci. High-level aminoglycoside resistance was assessed in 190 commensal erythromycin-resistant alpha-hemolytic streptococcal strains. Of these, seven were also aminoglycoside-resistant: one Streptococcus mitis strain was resistant to high levels of kanamycin and carried the aph(3 ')-III gene, four S. mitis strains were resistant to high levels of streptomycin and lacked aminoglycoside-modifying enzymes, and two S. oralis strains that were resistant to high levels of kanamycin and streptomycin harbored both the aph(3 ')-III and the ant(6) genes. The two S. oralis strains also carried the ant(6)-sat4- aph(3 ' ')-III aminoglycoside-streptothricin resistance gene cluster, but it was not contained in a Tn5405-like structure. The presence of this resistance gene cluster in commensal streptococci suggests an exchange of resistance genes between these bacteria and enterococci or staphylococci.200717407061
2914140.9994The genetic background for streptomycin resistance in Escherichia coli influences the distribution of MICs. OBJECTIVES: The aim of this study was to investigate the genetic background for streptomycin resistance in Escherichia coli and perform analysis of the MICs in relation to genetic background. METHODS: The 136 strains investigated, with streptomycin MICs of > or =16 mg/L, originated from meat and meat products and were collected within the frame of the Norwegian monitoring programme for antimicrobial resistance in bacteria from feed, food and animals (NORM-VET). PCR was carried out for detection of the streptomycin resistance genes strA-strB and the integron-associated aadA gene cassettes. RESULTS: The strA-strB genes and/or an aadA gene cassette were detected in 110 of the 136 (80.9%) strains investigated. The strA-strB genes were the most prevalent, and were detected in 90 strains. The aadA gene cassettes were detected in 29 strains, and nine strains harboured both the strA-strB genes and an aadA gene cassette. The distribution of MICs differed considerably between isolates harbouring the strA-strB genes (solely) (MIC(50) = 128 mg/L) and isolates harbouring an aadA gene cassette (solely) (MIC(50) = 16 mg/L). Strains harbouring both the strA-strB genes and an aadA gene cassette had higher streptomycin MICs than those harbouring either alone. CONCLUSIONS: The distribution of streptomycin MICs in E. coli can be greatly influenced by the genes encoding resistance to streptomycin. The strA-strB genes are probably involved in conferring high-level resistance to streptomycin, whereas the opposite seems to be the case for the aadA gene cassettes. The low-level streptomycin resistance, caused by the presence of aadA gene cassettes in integrons, represents an obstacle in classifying E. coli as susceptible or resistant to streptomycin. Furthermore, the determination of an epidemiological cut-off value for surveillance purposes is also complicated by dissemination of integrons containing the aadA cassettes.200515897222
3569150.9994Identification of a new ribosomal protection type of tetracycline resistance gene, tet(36), from swine manure pits. Previously, only one ribosome protection type of a tetracycline resistance gene, tetQ, had been identified in Bacteroides spp. During an investigation of anaerobic bacteria present in swine feces and manure storage pits, a tetracycline-resistant Bacteroides strain was isolated. Subsequent analysis showed that this new Bacteroides strain, Bacteroides sp. strain 139, did not contain tetQ but contained a previously unidentified tetracycline resistance gene. Sequence analysis showed that the tetracycline resistance gene from Bacteroides sp. strain 139 encoded a protein (designated Tet 36) that defines a new class of ribosome protection types of tetracycline resistance. Tet 36 has 60% amino acid identity over 640 aa to TetQ and between 31 and 49% amino acid identity to the nine other ribosome protection types of tetracycline resistance genes. The tet(36) region was not observed to transfer from Bacteroides sp. strain 139 to another Bacteroides sp. under laboratory conditions. Yet tet(36) was found in other genera of bacteria isolated from the same swine manure pits and from swine feces. Phylogenetic analysis of the tet(36)-containing isolates indicated that tet(36) was present not only in the Cytophaga-Flavobacter-Bacteroides group to which Bacteroides sp. strain 139 belongs but also in gram-positive genera and gram-negative proteobacteria, indicating that horizontal transfer of tet(36) is occurring between these divergent phylogenetic groups in the farm environment.200312839793
2919160.9994Occurrence of Transferable Integrons and sul and dfr Genes Among Sulfonamide-and/or Trimethoprim-Resistant Bacteria Isolated From Chilean Salmonid Farms. Salmon farming industry in Chile currently uses a significant quantity of antimicrobials to control bacterial pathologies. The main aims of this study were to investigate the presence of transferable sulfonamide- and trimethoprim-resistance genes, sul and dfr, and their association with integrons among bacteria associated to Chilean salmon farming. For this purpose, 91 Gram-negative strains resistant to sulfisoxazole and/or trimethoprim recovered from various sources of seven Chilean salmonid farms and mainly identified as belonging to the Pseudomonas genus (81.0%) were studied. Patterns of antimicrobial resistance of strains showed a high incidence of resistance to florfenicol (98.9%), erythromycin (95.6%), furazolidone (90.1%) and amoxicillin (98.0%), whereas strains exhibited minimum inhibitory concentrations (MIC(90)) values of sulfisoxazole and trimethoprim of >4,096 and >2,048 μg mL(-1), respectively. Strains were studied for their carriage of these genes by polymerase chain reaction, using specific primers, and 28 strains (30.8%) were found to carry at least one type of sul gene, mainly associated to a class 1 integron (17 strains), and identified by 16S rRNA gene sequencing as mainly belonging to the Pseudomonas genus (21 strains). Of these, 22 strains carried the sul1 gene, 3 strains carried the sul2 gene, and 3 strains carried both the sul1 and sul2 genes. Among these, 19 strains also carried the class 1 integron-integrase gene intI1, whereas the dfrA1, dfrA12 and dfrA14 genes were detected, mostly not inserted in the class 1 integron. Otherwise, the sul3 and intI2 genes were not found. In addition, the capability to transfer by conjugation these resistance determinants was evaluated in 22 selected strains, and sul and dfr genes were successfully transferred by 10 assayed strains, mainly mediated by a 10 kb plasmid, with a frequency of transfer of 1.4 × 10(-5) to 8.4 × 10(-3) transconjugant per recipient cell, and exhibiting a co-transference of resistance to florfenicol and oxytetracycline, currently the most used in Chilean salmon industry, suggesting an antibacterial co-selection phenomenon. This is the first report of the characterization and transferability of integrons as well as sul and dfr genes among bacteria associated to Chilean salmon farms, evidencing a relevant role of this environment as a reservoir of these genes.201931031727
5919170.9994Self-transmissible antibiotic resistance to ampicillin, streptomycin, and tetracyclin found in Escherichia coli isolates from contaminated drinking water. Presence and survival of cultivable bacteria in drinking water can act as a vehicle to disseminate virulence genes (adherence, enterotoxigenic and antibiotic resistance) to other bacteria. This can result in high morbidity and mortality, and the failure of the treatment of life threatening bacterial infections in humans and animals. In this study, antibiotic resistance (ABR) patterns and transferability of the ABR markers was investigated in Escherichia coli isolates obtained from drinking water and human urine samples. The ABR in E. coli isolates was determined against 15 antibiotics commonly used in human and veterinary medicine. A high frequency of ABR to carbenicillin (56%), tetracycline (53%) and streptomycin (49%) and a low frequency of cefizoxime (5%), amikacin (8%), cefazidine, (5%), chloramphenicol (9%), and kanamycin (18%) was found in the tested E. coli isolates. ABR to kanamycin (0% vs. 35%) and moxalactam (4% vs. 30%) was higher in drinking water isolates whereas resistance to streptomycin (92% vs. 15%), ampicillin (24% vs. 10%), and nalidixic acid (12% vs. 0%) was higher in human urine isolates. A large number of E. coli isolates (93%) exhibited resistance to two or more antibiotics. Two of E. coli isolates from drinking water showed resistances to six (Cb Cm Cx Ip Mx Tc and An Cb Km Mx Sm Tc) and one was resistant to seven antibiotics (Am An Cb Km Mx Sm Tc). A majority of the multiple antibiotic resistant E. coli isolates contained one or more plasmids (size ranged approximately 1.4 Kb to approximately 40 Kb). The ABR traits (Am and Tc) were transferable to other bacteria via conjugation. These data raise an important question about the impact of E. coli containing self-transmissible R-plasmids as a potential reservoir of virulence genes in drinking water.200415055932
5921180.9994Prevalence of tetracycline resistance genes in oral bacteria. Tetracycline is a broad-spectrum antibiotic used in humans, animals, and aquaculture; therefore, many bacteria from different ecosystems are exposed to this antibiotic. In order to determine the genetic basis for resistance to tetracycline in bacteria from the oral cavity, saliva and dental plaque samples were obtained from 20 healthy adults who had not taken antibiotics during the previous 3 months. The samples were screened for the presence of bacteria resistant to tetracycline, and the tetracycline resistance genes in these isolates were identified by multiplex PCR and DNA sequencing. Tetracycline-resistant bacteria constituted an average of 11% of the total cultivable oral microflora. A representative 105 tetracycline-resistant isolates from the 20 samples were investigated; most of the isolates carried tetracycline resistance genes encoding a ribosomal protection protein. The most common tet gene identified was tet(M), which was found in 79% of all the isolates. The second most common gene identified was tet(W), which was found in 21% of all the isolates, followed by tet(O) and tet(Q) (10.5 and 9.5% of the isolates, respectively) and then tet(S) (2.8% of the isolates). Tetracycline resistance genes encoding an efflux protein were detected in 4.8% of all the tetracycline-resistant isolates; 2.8% of the isolates had tet(L) and 1% carried tet(A) and tet(K) each. The results have shown that a variety of tetracycline resistance genes are present in the oral microflora of healthy adults. This is the first report of tet(W) in oral bacteria and the first report to show that tet(O), tet(Q), tet(A), and tet(S) can be found in some oral species.200312604515
5849190.9994Characterisation and molecular cloning of the novel macrolide-streptogramin B resistance determinant from Staphylococcus epidermidis. A total of 110 staphylococcal isolates from human skin were found to express a novel type of erythromycin resistance. The bacteria were resistant to 14-membered ring macrolides (MIC 32-128 mg/l) but were sensitive to 16-membered ring macrolides and lincosamides. Resistance to type B streptogramins was inducible by erythromycin. A similar phenotype, designated MS resistance, was previously described in clinical isolates of coagulase-negative staphylococci from the USA. In the UK, MS resistance is widely distributed in coagulase-negative staphylococci but was not detected in 100 erythromycin resistant clinical isolates of Staphylococcus aureus. Tests for susceptibility to a further 16 antibiotics failed to reveal any other selectable marker associated with the MS phenotype. Plasmid pattern analysis of 48 MS isolates showed considerable variability between strains and no common locus for the resistance determinant. In one strain of S. epidermidis co-resistance to tetracycline, penicillin and erythromycin (MS) was associated with a 31.5 kb plasmid, pUL5050 which replicated and expressed all three resistances when transformed into S. aureus RN4220. The MS resistance determinant was localised to a 1.9 kb fragment which was cloned on to the high-copy-number vector, pSK265. A constitutive mutant of S. aureus RN4220 containing the 1.9 kb fragment remained sensitive to clindamycin. This observation, together with the concentration-dependent induction (optimum 5 mg/l of erythromycin) of virginiamycin S resistance suggests that the MS phenotype is not due to altered expression of MLS resistance determinants (erm genes) but probably occurs via a different mechanism.19892559912