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PubMed2005

High prevalence of the plasmid-mediated quinolone resistance determinant qnrA in multidrug-resistant Enterobacteriaceae from blood cultures in Liverpool, UK.

OBJECTIVES: To determine the prevalence of the plasmid-mediated quinolone resistance qnrA gene in a selected collection of blood culture isolates of Enterobacteriaceae resistant to both ciprofloxacin and cefotaxime. METHODS: Over a 29 month period, a total of 47 non-repetitive isolates of Enterobacteriaceae resistant to both ciprofloxacin and cefotaxime were identified. Isolates were screened for the presence of the qnrA gene, class I integrons and bla(ESBL) by PCR. Transferability was examined by conjugation with the sodium azide-resistant Escherichia coli J53. All qnrA-positive isolates were examined for DNA-relatedness by PFGE. RESULTS: A total of 15 of the 47 test isolates (32%) were positive for the qnrA gene, and included single isolates of E. coli and Citrobacter freundii, 4 Klebsiella pneumoniae and 9 Enterobacter cloacae. All 15 qnrA-positive isolates carried class 1 integrons, and 11 the extended-spectrum beta-lactamase gene bla(SHV-12). By PFGE two K. pneumoniae and three E. cloacae, respectively, were considered clonally but not temporally related. Plasmid transfer of quinolone resistance was only achieved with single isolates of K. pneumoniae and E. cloacae. Both plasmids carried class 1 integrons with a pSAL-1-like gene cassette arrangement intl1-aadA2-qacEDelta-sul1. CONCLUSIONS: In this selected group of ciprofloxacin- and cefotaxime-resistant bacteria, carriage of the qnrA gene was high (32%). This compares with <2.0% as demonstrated in worldwide studies of laboratory collections of ciprofloxacin-resistant bacteria. The majority of qnrA-positive isolates in our study originated from high-dependency care units within our hospital, but were shown not to be clonal by PFGE. This is the first report of qnrA-positive Enterobacteriaceae in the United Kingdom.

Anti-Bacterial Agents↗
PubMed2006

Phenotypic and genotypic characterization of antimicrobial resistance in Escherichia coli O111 isolates.

OBJECTIVES: The aim of this study was to generate baseline data on the prevalence and molecular basis of antimicrobial resistance in Escherichia coli O111 isolates. METHODS: A total of 105 epidemiologically unrelated E. coli O111 isolates from humans and cattle (isolated between 1983 and 2003) were tested for susceptibility to 17 antimicrobial agents by broth microdilution. Resistant isolates were screened by molecular methods for resistance genes, class 1 and 2 integrons and mutations in the quinolone-resistance determining regions. RESULTS: Resistance was found in 76% of the isolates, with a prevalence of 72% for multiresistance. The most prevalent resistances were to streptomycin, sulfamethoxazole and tetracycline (72-68%), followed by spectinomycin, ampicillin and kanamycin/neomycin (39-25%). For each antimicrobial agent, the predominant resistance genes were ampicillin, bla(TEM) (94%); chloramphenicol, catA1 (100%); gentamicin, aac(3)-IV and aac(3)-II (50% each); kanamycin, aphA1 (100%); streptomycin, aadA1- like (66%); sulfamethoxazole, sul1 (59%); tetracycline, tet(A) (86%); and trimethoprim, dfrA1-like (83%). Class 1 integrons were found in 41% of the isolates. They carried aadA1, dfrA1-aadA1 and dfrA15-aadA1. A class 2 integron (dfrA1-sat1-aadA1) was found in one isolate. Only three isolates (3%) were resistant to nalidixic acid (reduced susceptibility to ciprofloxacin), with a single mutation in the gyrA gene. CONCLUSIONS: E. coli O111 strains exhibit a wide repertoire of genetic elements to sustain antimicrobial pressure. Two specific antimicrobial resistance pheno/genotypes, [STR-SPT]-SUL-TET/aadA1-sul1-tet(A) and STR-SUL-TET-AMP-[KAN-NEO]/strA/B-sul2-tet(A)-bla(TEM)-aphA1, are predominant.

Animals↗
PubMed2006

The prevalence of, associations between and conjugal transfer of antibiotic resistance genes in Escherichia coli isolated from Norwegian meat and meat products.

OBJECTIVES: To investigate the distribution of, associations between and the transferability of antimicrobial resistance genes in resistant Escherichia coli strains isolated from Norwegian meat and meat products. METHODS: The 241 strains investigated were collected within the frame of the Norwegian monitoring programme for antimicrobial resistance in bacteria from feed, food and animals (NORM-VET) during the years 2000-2003. PCR was carried out for detection of resistance genes. Conjugation experiments were carried out with the resistant isolates from meat as donor strains and E. coli DH5alpha as the recipient strain. Statistical analyses were performed with the SAS-PC-System version 9.1 for Windows. RESULTS: Resistance genes common in pathogenic E. coli were frequently found among the isolates investigated. Strains harbouring several genes encoding resistance to the same antimicrobial agent were significantly (P < 0.0001) more frequently multiresistant than others. Strong positive associations were found between the tet(A) determinant and the genetic elements sul1, dfrA1 and aadA1. Negative associations were found between resistance genes encoding resistance to the same antimicrobial agent: tet(A)/tet(B), sul1/sul2 and strA-strB/aadA1. The resistance genes were successfully transferred from 38% of the isolates. The transfer was more frequent from resistant isolates harbouring class 1 integrons (P < 0.001). CONCLUSIONS: Acquired resistance played a major role in conferring resistance among the isolates investigated. The possibility of transferring resistance increases both by increased multiresistance and by the presence of class 1 integrons. The conjugation experiments suggest that tet(A) and class 1 integrons are often located on the same conjugative plasmid.

Animals↗
PubMed2006

Molecular characterization of ciprofloxacin-resistant Salmonella enterica serovar Typhi and Paratyphi A causing enteric fever in India.

OBJECTIVES: To define the genetic characteristics and resistance mechanisms of clinical isolates of Salmonella enterica serovar Typhi (S. Typhi) and S. enterica serovar Paratyphi A (S. Paratyphi A) exhibiting high-level fluoroquinolones resistance. METHODS: Three S. Typhi and two S. Paratyphi A ciprofloxacin-resistant isolates (MICs > 4 mg/L) were compared with isolates with reduced susceptibility to ciprofloxacin (MICs 0.125-1 mg/L) by PFGE, plasmid analysis, presence of integrons and nucleotide changes in topoisomerase genes. RESULTS: In S. Typhi and Paratyphi A, a single gyrA mutation (Ser-83-->Phe or Ser-83-->Tyr) was associated with reduced susceptibility to ciprofloxacin (MICs 0.125-1 mg/L); an additional mutation in parC (Ser-80-->Ile, Ser-80-->Arg, Asp-69-->Glu or Gly-78-->Asp) was accompanied by an increase in ciprofloxacin MIC (> or = 0.5 mg/L). Three mutations conferred ciprofloxacin resistance: two in gyrA (Ser-83-->Phe and Asp-87-->Asn or Asp-87-->Gly) and one in parC. This is the first report of parC mutations in S. Typhi. Ciprofloxacin-resistant S. Typhi and S. Paratyphi A differed in their MICs and mutations in gyrA and parC. Moreover S. Typhi harboured a 50 kb transferable plasmid carrying a class 1 integron (dfrA15/aadA1) that confers resistance to co-trimoxazole and tetracycline but not to ciprofloxacin. PFGE revealed undistinguishable XbaI fragment patterns in ciprofloxacin-resistant S. Typhi as well as in S. Paratyphi A isolates and showed that ciprofloxacin-resistant S. Typhi have emerged from a clonally related isolate with reduced susceptibility to ciprofloxacin after sequential acquisition of a second mutation in gyrA. CONCLUSIONS: To our knowledge this is the first report of molecular characterization of S. Typhi with full resistance to ciprofloxacin. Notably, the presence of a plasmid-borne integron in ciprofloxacin-resistant S. Typhi may lead to a situation of untreatable enteric fever.

Amino Acid Substitution↗
PubMed2005

Genomic analysis of a multidrug-resistant strain of enterohaemorrhagic Escherichia coli O157:H7 causing a family outbreak in Japan.

A family outbreak of enterohaemorrhagic Escherichia coli (EHEC) O157:H7 infection occurred in October 2003 in the Hiroshima prefecture, Japan. Four isolates of EHEC O157:H7, 03064, 03065, 03066 and 03067, were recovered from a 1-year-old daughter, mother, father and 3-year-old daughter, respectively. All EHEC O157:H7 isolates were positive for Stx1 and Stx2 Shiga toxins. Surprisingly, DNA fingerprinting profiles obtained by PFGE showed that the first isolate, 03064, had unique XbaI and BlnI profiles that differed from the other three isolates. Also, plasmid analysis results revealed that isolate 03064 contained an extra plasmid larger than the classic large plasmid of EHEC O157, pO157 (93.6 kb). This new plasmid was named pMDR157. Furthermore, isolate 03064 showed a multidrug-resistance (MDR) phenotype against streptomycin, spectinomycin, co-trimoxazole (trimethoprim/sulfamethoxazole), ampicillin and tetracycline; the other isolates were completely sensitive to these antibiotics. Molecular analysis of the MDR phenotype in this unique strain revealed the presence of a class 1 integron containing two gene cassettes: a dihydrofolate reductase type 1 gene (dfrI), which confers resistance to trimethoprim, and an aminoglycoside adenyltransferase gene (aadA1), which confers resistance to streptomycin and spectinomycin. Southern blot hybridization showed that the class 1 integron was located in the extra plasmid, pMDR157. The ampicillin resistance was found to be due to the presence of the TEM-1-type beta-lactamase gene. The MDR phenotype was transferred successfully to E. coli HB101 by conjugation, indicating that both the class 1 integron and the TEM-1 beta-lactamase were located on the conjugative transferable plasmid, pMDR157. To the authors' knowledge, this is the first report of the identification of a beta-lactamase gene in EHEC O157.

Anti-Bacterial Agents↗
PubMed2003

Comparative analysis of superintegrons: engineering extensive genetic diversity in the Vibrionaceae.

Integrons are natural tools for bacterial evolution and innovation. Their involvement in the capture and dissemination of antibiotic-resistance genes among Gram-negative bacteria is well documented. Recently, massive ancestral versions, the superintegrons (SIs), were discovered in the genomes of diverse proteobacterial species. SI gene cassettes with an identifiable activity encode proteins related to simple adaptive functions, including resistance, virulence, and metabolic activities, and their recruitment was interpreted as providing the host with an adaptive advantage. Here, we present extensive comparative analysis of SIs identified among the Vibrionaceae. Each was at least 100 kb in size, reaffirming the participation of SIs in the genome plasticity and heterogeneity of these species. Phylogenetic and localization data supported the sedentary nature of the functional integron platform and its coevolution with the host genome. Conversely, comparative analysis of the SI cassettes was indicative of both a wide range of origin for the entrapped genes and of an active cassette assembly process in these bacterial species. The signature attC sites of each species displayed conserved structural characteristics indicating that symmetry rather than sequence was important in the recognition of such a varied collection of target recombination sequences by a single site-specific recombinase. Our discovery of various addiction module cassettes within each of the different SIs indicates a possible role for them in the overall stability of large integron cassette arrays.

Attachment Sites, Microbiological↗
PubMed2002

Low-virulence Citrobacter species encode resistance to multiple antimicrobials.

Citrobacter spp. are gram-negative commensal bacteria that infrequently cause serious nosocomial infections in compromised hosts. They are often resistant to cephalosporins due to overexpression of their chromosomal beta-lactamase. During a recent study of multidrug-resistant Enterobacteriaceae (MDRE) in solid-organ transplant patients, we found that almost half of patients colonized with MDRE carried one or more cefpodoxime-resistant Citrobacter freundii, Citrobacter braakii, or Citrobacter amalonaticus strains. Pulsed-field gel electrophoresis showed that 36 unique strains of Citrobacter were present among 32 patients. Genetic and phenotypic analysis of the resistance mechanisms of these bacteria showed that the extended-spectrum beta-lactamase (ESBL) SHV-5 or SHV-12 was encoded by 8 strains (26%) and expressed by 7 strains (19%). A number of strains were resistant to other drug classes, including aminoglycosides (28%), trimethoprim-sulfamethoxazole (31%), and fluoroquinolones (8%). PCR and DNA analysis of these multiresistant strains revealed the presence of class I integrons, including the first integrons reported for C. braakii and C. amalonaticus. The integrons encoded aminoglycoside resistance, trimethoprim resistance, or both. Despite the prevalence of MDR Citrobacter spp. in our solid-organ transplant patients, only a single infection with a colonizing strain was recorded over 18 months. Low-virulence Citrobacter spp., which can persist in the host for long periods, could influence pathogen evolution by accumulation of genes encoding resistance to multiple antimicrobial classes.

Citrobacter↗
PubMed2003

Antimicrobial resistance genes in enterotoxigenic Escherichia coli O149:K91 isolates obtained over a 23-year period from pigs.

A total of 112 Escherichia coli O149:K91 strains isolated from pigs with diarrhea in Quebec, Canada, between 1978 and 2000 were characterized for their genotypic antimicrobial resistance profiles. Tests for resistance to 10 antimicrobial agents were conducted. Resistance to tetracycline and sulfonamides was found to be the most frequent, but resistance to cefotaxime and ceftiofur was absent. An increase in the number of isolates resistant to at least three antimicrobials was observed over time. The distribution of 28 resistance genes covering six antimicrobial families (beta-lactams, aminoglycosides, phenicols, tetracycline, trimethoprim, and sulfonamides) was assessed by colony hybridization. Significant differences in the distributions of tetracycline [tet(A), tet(B), tet(C)], trimethoprim (dhfrI, dhfrV, dhfrXIII), and sulfonamide (sulI, sulII) resistance genes were observed during the study period (1978 to 2000). Sixty percent of the isolates possessed a class 1 integron, illustrating the importance of integrons in the epidemiology of antibiotic resistance in E. coli strains from pigs. Amplification of the integron's variable region resulted in four distinct fragments of 1, 1.3, 1.6, and 1.8 kb, with the 1.6- and 1.8-kb fragments appearing only during the last half of the study period. Examination of linkages among the different resistance genes showed a variety of positive and negative associations. Association analysis of isolates divided into two groups, those isolated between 1978 and 1989 and those isolated between 1990 and 2000, revealed the appearance of new positive resistance gene associations. Our genotypic resistance analyses of ETEC isolates from pigs indicate that many of the antibiotic resistance genes behind phenotypic resistance are not static but, rather, are in a state of flux driven by various selection forces such as the use of specific antimicrobials.

Animals↗
PubMed2004

Molecular characterization of a beta-lactamase gene, blaGIM-1, encoding a new subclass of metallo-beta-lactamase.

As part of the SENTRY Antimicrobial Surveillance Program in 2002, five multidrug-resistant Pseudomonas aeruginosa clinical isolates were detected with metallo-beta-lactamase (MbetaL) activity. The isolates were recovered from different patients in a medical center located in Dusseldorf, Germany. The resistant determinant was isolated amplifying the region between the integrase and the aacA4 gene cassette. Sequencing revealed a novel MbetaL gene, designated bla(GIM-1). Additional analysis showed that GIM-1, comprising 250 amino acids and with a pI value of 5.4, differs in its primary sequence from that described for IMP, VIM, and SPM-1 enzymes by 39 to 43%, 28 to 31%, and 28%, respectively. The enzyme possesses unique amino acids within the major consensus sequence (HXHXD) of the MbetaL family. Kinetics analysis revealed that GIM-1 has no clear preference for any substrate and did not hydrolyze azlocillin, aztreonam, and the serine-beta-lactamase inhibitors. bla(GIM-1) was found on a 22-kb nontransferable plasmid. The new MbetaL gene was embedded in the first position of a 6-kb class 1 integron, In77, with distinct features, including an aacA4 cassette downstream of the MbetaL gene that appeared to be truncated with bla(GIM-1). The aacA4 was followed by an aadA1 gene cassette that was interrupted by a copy of the IS1394. This integron also carried an oxacillinase gene, bla(OXA-2), before the 3'-CS region. GIM-1 appears to be a unique MbetaL, which is located in a distinct integron structure, and represents the fourth subclass of mobile MbetaL enzymes to be characterized.

Amino Acid Sequence↗
PubMed2006

Molecular epidemiology of acquired-metallo-beta-lactamase-producing bacteria in Poland.

We have analyzed 40 metallo-beta-lactamase (MBL)-producing isolates of Pseudomonas aeruginosa (n = 38), Pseudomonas putida (n = 1), and Acinetobacter genospecies 3 (n = 1) from 17 hospitals in 12 cities in Poland that were identified in 2000 to 2004. Pulsed field gel electrophoresis typing classified the P. aeruginosa isolates into eight types, with two types differentiated further into subtypes. Each of the types was specific either to a given center or to several hospitals of the same or neighboring geographic area. Almost all of the organisms produced beta-lactamase VIM-2; the only exceptions were several P. aeruginosa isolates from two centers which expressed VIM-4. The bla(VIM) genes resided exclusively within class 1 integrons, and these were located in either chromosomal or plasmid DNA. PCR-restriction fragment length polymorphism study of the variable regions of the integrons, followed by DNA sequencing, revealed the presence of eight different, mostly novel gene cassette arrays, six of which contained bla(VIM-2) and two of which contained bla(VIM-4). The occurrence of the integron variants correlated well with the geographic distribution of the MBL-producing organisms, and this suggested that their emergence in particular parts of the country had been likely due to a number of independent events. The following regional dissemination of MBL producers could be attributed to various phenomena, including their clonal spread, horizontal transmission of resistance determinants, or both. All of the data collected in this study revealed that even at this early stage of detection, the epidemiological situation concerning MBL producers in Poland has already been complex and very dynamic.

Acinetobacter↗
PubMed2004

Characterization of multiple-antimicrobial-resistant salmonella serovars isolated from retail meats.

A total of 133 Salmonella isolates recovered from retail meats purchased in the United States and the People's Republic of China were assayed for antimicrobial susceptibility, the presence of integrons and antimicrobial resistance genes, and horizontal transfer of characterized antimicrobial resistance determinants via conjugation. Seventy-three (82%) of these Salmonella isolates were resistant to at least one antimicrobial agent. Resistance to the following antibiotics was common among the United States isolates: tetracycline (68% of the isolates were resistant), streptomycin (61%), sulfamethoxazole (42%), and ampicillin (29%). Eight Salmonella isolates (6%) were resistant to ceftriaxone. Fourteen isolates (11%) from the People's Republic of China were resistant to nalidixic acid and displayed decreased susceptibility to ciprofloxacin. A total of 19 different antimicrobial resistance genes were identified in 30 multidrug-resistant Salmonella isolates. The bla(CMY-2) gene, encoding a class A AmpC beta-lactamase, was detected in all 10 Salmonella isolates resistant to extended-spectrum beta-lactams. Resistance to ampicillin was most often associated with a TEM-1 family beta-lactamase gene. Six aminoglycoside resistance genes, aadA1, aadA2, aacC2, Kn, aph(3)-IIa, and aac(3)-IVa, were commonly present in the Salmonella isolates. Sixteen (54%) of 30 Salmonella isolates tested had integrons ranging in size from 0.75 to 2.7 kb. Conjugation studies demonstrated that there was plasmid-mediated transfer of genes encoding CMY-2 and TEM-1-like beta-lactamases. These data indicate that Salmonella isolates recovered from retail raw meats are commonly resistant to multiple antimicrobials, including those used for treating salmonellosis, such as ceftriaxone. Genes conferring antimicrobial resistance in Salmonella are often carried on integrons and plasmids and could be transmitted through conjugation. These mobile DNA elements have likely played an important role in transmission and dissemination of antimicrobial resistance determinants among Salmonella strains.

Animals↗
PubMed2002

Nosocomial infections caused by multidrug-resistant isolates of pseudomonas putida producing VIM-1 metallo-beta-lactamase.

Successful carbapenem-based chemotherapy for the treatment of Pseudomonas infections has been seriously hindered by the recent appearance of IMP- and VIM-type metallo-beta-lactamases, which confer high-level resistance to carbapenems and most other beta-lactams. Recently, multidrug-resistant Pseudomonas putida isolates for which carbapenem MICs were >/=32 micro g/ml were recovered from cultures of urine from three inpatients in the general intensive care unit of the Ospedale di Circolo, Varese, Italy. Enzyme assays revealed production of a metallo-beta-lactamase activity, while molecular analysis detected in each isolate a bla(VIM-1) determinant carried by an apparently identical medium-sized plasmid. Conjugation experiments were unsuccessful in transferring the beta-lactamase determinant to Escherichia coli or Pseudomonas aeruginosa. Macrorestriction analysis by pulsed-field gel electrophoresis demonstrated that the isolates were of clonal origin. PCR mapping and sequencing of the variable region of the plasmid-borne class 1 integron carrying the bla(VIM-1) determinant (named In110) showed that the bla(VIM-1)-containing cassette was identical to that previously found in strains of different species from other Italian hospitals and that the cassette array of In110 was not identical but clearly related to that of In70 (a bla(VIM-1)-containing plasmid-borne integron from an Achromobacter xylosoxidans isolate), pointing to a common origin of this cassette and to a related evolutionary history of their cognate integrons.

Aged↗
PubMed2004

Characterization of multiple-antimicrobial-resistant Escherichia coli isolates from diseased chickens and swine in China.

Escherichia coli isolates from diseased piglets (n = 89) and chickens (n = 71) in China were characterized for O serogroups, virulence genes, antimicrobial susceptibility, class 1 integrons, and mechanisms of fluoroquinolone resistance. O78 was the most common serogroup identified (63%) among the chicken E. coli isolates. Most isolates were PCR positive for the increased serum survival gene (iss; 97%) and the temperature-sensitive hemagglutinin gene (tsh; 93%). The O serogroups of swine E. coli were not those typically associated with pathogenic strains, nor did they posses common characteristic virulence factors. Twenty-three serogroups were identified among the swine isolates; however, 38% were O nontypeable. Overall, isolates displayed resistance to nalidixic acid (100%), tetracycline (98%), sulfamethoxazole (84%), ampicillin (79%), streptomycin (77%), and trimethoprim-sulfamethoxazole (76%). Among the fluoroquinolones, resistance ranged between 64% to levofloxacin, 79% to ciprofloxacin, and 95% to difloxacin. DNA sequencing of gyrA, gyrB, parC, and parE quinolone resistance-determining regions of 39 nalidixic acid-resistant E. coli isolates revealed that a single gyrA mutation was found in all of the isolates; mutations in parC together with double gyrA mutations conferred high-level resistance to fluoroquinolones (ciprofloxacin MIC, >/=8 microg/ml). Class 1 integrons were identified in 17 (19%) isolates from swine and 42 (47%) from chickens. The majority of integrons possessed genes conferring resistance to streptomycin and trimethoprim. These findings suggest that multiple-antimicrobial-resistant E. coli isolates, including fluoroquinolone-resistant variants, are commonly present among diseased swine and chickens in China, and they also suggest the need for the introduction of surveillance programs in China to monitor antimicrobial resistance in pathogenic bacteria that can be potentially transmitted to humans from food animals.

Animals↗
PubMed2006

Role of coresistance in the development of resistance to chloramphenicol in Escherichia coli isolated from sick cattle and pigs.

OBJECTIVE: To determine the cause of persistent resistance to chloramphenicol (CP) after the ban on its use in food-producing animals in several countries. SAMPLE POPULATION: 71 CP-resistant and 104 CP-susceptible Escherichia coli strains isolated from sick cattle and pigs in Japan. PROCEDURE: Susceptibility of all bacterial strains to thiamphenicol (TP) and florfenicol (FFC) was tested by use of an agar dilution method. The CP-resistance genes and variable region within class 1 integrons in CP-resistant strains were identified by use of a PCR assay. RESULTS: The CP acetyltransferase gene (ie, cat1) was identified as the predominant CP-resistance gene in strains isolated from cattle, and the cat1and nonenzymatic CP-resistance gene (ie, cmlA) were the predominant CP-resistance genes in strains isolated from pigs. Additionally, strains with cat1 isolated from cattle often were resistant to ampicillin, dihydrostreptomycin (DSM), oxytetracycline, and trimethoprim (TMP), whereas strains with cat1 or cmlA isolated from pigs often were resistant to DSM and TMP. Class 1 integrons were significantly more prevalent in strains with CP-resistance genes, compared with prevalence in strains without CP-resistance genes. All gene cassettes within the integrons were involved in resistance to DSM, TMP, or both. CONCLUSIONS AND CLINICAL RELEVANCE: Coresistance that develops because of the use of DSM and TMP in cattle and pigs apparently contributes to the selection of CP-resistant strains of E coli. Thus, it is possible that bacterial resistance to CP in animals would persist despite a ban on the use of CP in cattle and pigs.

Animals↗
PubMed2005

Molecular characterization of multidrug-resistant Proteus mirabilis isolates from retail meat products.

Sixty-four multidrug-resistant isolates of Proteus mirabilis were collected from retail meat products in Oklahoma. The isolates showed four different patterns of antibiotic resistance based on their resistant phenotype and genotypes. Most of these isolates were resistant to ampicillin, tetracycline, gentamycin, and kanamycin. Class 1 integrons were detected as a common carrier of the antibiotic-resistant genes, such as aadA1, aadB, and aadA2. A few isolates (9%) contained class 2 integrons with three gene cassettes included: dhfr1, sat1, and aadA1. These isolates were even resistant to nalidixic acid due to mutations in gyrA and parC. All ampicillin-resistant isolates contained blaTEM-1. Plasmids that contained class 1 or 2 integrons and blaTEM-1 were able to be transferred from P. mirabilis isolates into Escherichia coli by conjugation, indicating that conjugal transfer could contribute to the dissemination of antibiotic resistance genes between the Enterobacteriaceae species.

Anti-Bacterial Agents↗
PubMed2003

[Study on the molecular mechanism of transferable multiple-antibiotic resistance in extended-spectrum beta-lactamase-producing clinical isolates].

OBJECTIVE: To investigate the molecular mechanism of transferable multiple-antibiotic resistance in extended-spectrum beta-lactamases (ESBLs) producing isolates. METHODS: Antibiotics susceptibility was tested by E-test method, and multi-resistance plasmids were screened and isolated by extracting transformant plasmids. Inserted gene Cassettes of class 1 integron were amplified and analyzed by polymerase chain reaction (PCR) and DNA sequencing. RESULTS: Eight of the nine ESBL-producing plasmids were found to comprise class 1 integron sequence, of them 7 harbored 1 or 2 antibiotic resistant gene cassettes which encoding resistance to aminoglycosides (aacA4, aadA2 or aadA5), trimethoprim (dhfrA12 or dfrA17), rifampicin (arr-3) and chloramphenicol (cmlA6). The function of these gene cassettes corresponded to the resistance profiles of their electro-transformants. CONCLUSION: Multi-resistance gene cassettes located on plasmids and mediated by class 1 integron may play an important role in causing the development and dissemination of multiple-antibiotic resistance in ESBL-producing clinical isolates.

Anti-Bacterial Agents↗
PubMed2003

[Intercontinental spread of a trimethoprim-resistant strain of Shigella flexneri].

INTRODUCTION: In this study we characterize a trimethoprim-resistant strain of Shigella flexneri recovered from stool samples of an international traveler after a trip to Kenya, and analyze its epidemiological relationship with a set of strains having similar characteristics from Tanzania. METHODS: Clonal relationships were studied by three techniques - plasmid profile, repetitive-element (REP)-PCR and pulse-field gel electrophoresis (PFGE). The presence of type 1 integrons was studied by PCR and sequencing. The location and transferability of the detected integron was analyzed by conjugation and PCR. RESULTS: The epidemiological studies showed that all six strains studied belonged to the same clone. Furthermore, all of them carried the same gene encoding for trimethoprim resistance (dfrA7), which was located in an integron within a chromosome. CONCLUSION: Continuous epidemiological surveillance is required to control the spread of pathogenic microorganisms and the dissemination of resistance-encoding genes among geographical areas.

Bacterial Proteins↗
PubMed2001

Outbreaks and sporadic cases of Salmonella serovar panama studied by DNA fingerprinting and antimicrobial resistance.

In the Principality of Asturias (PA), Spain. three Salmonella serovar Panama outbreaks were registered in August 1998. In order to achieve an accurate identification of the strains implicated in the outbreaks and to study the molecular epidemiology of this serovar in the PA, the isolates collected over 1990-1999 were examined by DNA fingerprinting and antimicrobial resistance analysis. The origin of the isolates was: human (65, of which 20 were associated with the three outbreaks), octopus (2), beef (2), eggs (7), poultry faeces (2), sea water (5), sewage (2) and unknown (1). Sixteen lineages were defined by ribotyping, enterobacterial repetitive intergenic consensus sequences analysis, and randomly amplified polymorphic DNA segment analysis. One lineage was endemic in the PA and was also represented by isolates from other Spanish regions. The organisms of this lineage can be differentiated (by resistance-, plasmid- and integron-profiles) into 19 types. The three outbreaks were caused by organisms falling into a single type (nalidixic acid-resistant, plasmid- and integron-free) belonging to the endemic lineage, which was associated with poultry as the reservoir. Isolates showing drug-resistance (71%) fell into six lineages and 23 types. Ten multidrug-resistant types carried class I integrons with three types of variable regions containing resistance gene cassettes.

Animals↗