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Yang J.,Chinese PLA General Hospital | Luo Y.,Chinese PLA General Hospital | Cui S.,National Center for Surveillance of Antimicrobial Resistance | Wang W.,Center for Hospital Infection Control | Han L.,Center for Hospital Infection Control
Microbial Drug Resistance | Year: 2011

A total of 59 and 74 nonduplicate plasmid-mediated quinolone resistance (PMQR) genes-carrying Klebsiella pneumoniae and Escherichia coli isolates were collected. All strains were assayed for fluoroquinolone susceptibility and the prevalence of quinolone resistance-determining regions (QRDRs) mutation. The association between PMQR determinants and common β-lactamase genes was also analyzed. Genetic relatedness of the isolates was analyzed by pulsed-field gel electrophoresis (PFGE). The PMQR genes-carrying K. pneumoniae and E. coli isolates exhibited high fluoroquinolone resistance rates, indicating that PMQR determinants play an essential role in the development of fluoroquinolone resistance. Remarkably, most qnr-carrying strains had only a single or no QRDR mutation in GyrA or ParC, and most exhibited decreased ciprofloxacin (CIP) susceptibility or low-level CIP resistance. However, 71.4% and 98.4% of qnr-negative K. pneumoniae and E. coli contained double QRDR mutations, and most presented high-level CIP resistance. Additionally, K. pneumoniae presented a lower CIP resistance rate than E. coli (59.3% vs. 91.9%) and low carriage of double QRDR mutations (38.9% vs. 89.9%). Also, most (88.1%) K. pneumoniae examined in this study carried qnr and only 14.9% of E. coli were qnr positive. Thus, the high fluoroquinolone susceptibility of K. pneumoniae isolates is primarily due to fewer QRDR substitutions as a result of high prevalence of qnr alleles in the host. Our findings support the hypothesis that chromosomal resistance mutations could be affected by the presence of Qnr, in other words, Qnr may protect the QRDR domains in the gyrase and topoisomerase IV from mutations under the inhibition of fluoroquinolones. Another remarkable finding was that the PMQR genes-carrying K. pneumoniae exhibited much higher proportions of extended-spectrum β-lactamases (ESBLs)-positive phenotype than E. coli (73.5% vs. 59.5%). This is due to not only the high prevalence of SHV-type ESBL-conferring enzymes in K. pneumoniae but also the interference of DHA-producing K. pneumoniae as a result of the strong association between qnrB and blaDHA. © 2011, Mary Ann Liebert, Inc.

Li J.,National Center for Surveillance of Antimicrobial Resistance | Ma Y.,National Center for Surveillance of Antimicrobial Resistance | Hu C.,National Center for Surveillance of Antimicrobial Resistance | Jin S.,National Center for Surveillance of Antimicrobial Resistance | And 4 more authors.
Foodborne Pathogens and Disease | Year: 2010

The objective of this study was to investigate the distribution of extended spectrum β-lactamase (ESBL)-producing Escherichia coli isolates in swine and poultry farms in China. Rectal or cloaca swabs of swine and chicken were collected from four province-level regions of China, and E. coli isolates were recovered and tested for antimicrobial susceptibility. The isolates producing ESBLs were further characterized by pulsed-field gel electrophoresis (PFGE) and sequence analysis of genes encoding β -lactamases and class I integrons. In total, 156 and 224 E. coli isolates were recovered from rectal swabs of four swine farms and cloaca swabs of six chicken farms, respectively. Prevalence of resistant isolates was higher in chicken than in swine. Fifty-six isolates producing ESBLs were identified from chicken samples, but no ESBL-producing isolates were identified from swine samples. Of 56 ESBL-producing isolates, 54 isolates contained cefotaxime (CTX)-M type β-lactamases, including bla CTX-M-14 (nCTX-M-65 (n=13), blaCTX-M-55 (n=10), blaCTX-M-24 (n=3), blaCTX-M-3 (n=2), bla CTX-M-15 (n=1), and blaCTX-M-64 (n=1). Among 54 E. coli isolates containing blaCTX-M, 11 PFGE clusters and 42 PFGE patterns were identified. More importantly, more than three-fourth of the ESBL-producing isolates in chicken were also resistant to ciprofloxacin. Our data demonstrated that chicken had become an important reservoir of blaCTX-M in China. Detailed molecular comparison of plasmids and genomes of isolates from various sources will help to better define the transmission dynamics of bla CTX-M between humans and food-producing animals. Copyright 2010, Mary Ann Liebert, Inc.

Yang J.,General Hospital of PLA | Luo Y.,General Hospital of PLA | Li J.,National Center for Surveillance of Antimicrobial Resistance | Ma Y.,National Center for Surveillance of Antimicrobial Resistance | And 4 more authors.
Journal of Antimicrobial Chemotherapy | Year: 2010

Background: The categories of recognized transferable quinolone resistance determinants have been increasing sharply. The rapid horizontal transfer of these quinolone resistance genes has caused concern since they bring new dissemination possibilities for quinolone resistance. Methods: In total, 579 clinical Escherichia coli isolates were subjected to antimicrobial susceptibility testing, screening for qnr alleles, qepA and aac-(6')-Ib-cr by PCR amplification and DNA sequence analysis. Isolates containing transferable quinolone resistance determinants were further characterized by mutation analysis in the quinolone resistance determining regions (QRDRs) of GyrA and ParC, phylogenetic typing and PFGE to determine their genetic relatedness. Results: After PCR screening and sequence analysis, transferable quinolone resistance determinants were identified in 74 of 579 E. coli isolates (12.8%). The antimicrobial resistance profiles and phylogenetic groups differed between isolates containing different categories of transferable quinolone resistance determinant. Most of the isolates containing qepA alone were highly resistant to ciprofloxacin (MIC≥512 mg/L) and belonged to phylogenetic group D (22/25), while most of the isolates containing aac-(6')-Ib-cr alone belonged to phylogenetic group A (17/35) or D (16/35). Of 74 E. coli isolates containing transferable quinolone resistance determinants, 69 PFGE patterns and 19 clusters were identified. Conclusions: The great genetic variation of E. coli hosts containing transferable quinolone resistance determinants demonstrated the high transmission capacity of these mechanisms. It is urgent to characterize and block their transmission routes in order that the utility of quinolones is preserved. © The Author 2010. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy.

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