Plasmid-mediated quinolone resistance determinants qnr and aac(6′)-Ib-cr in extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae in China

• Published in: Journal of antimicrobial chemotherapy 2008-05, Vol.61 (5), p.1003-1006
• Main Authors: Jiang, Yan, Zhou, Zhihui, Qian, Ying, Wei, Zeqing, Yu, Yunsong, Hu, Songnian, Li, Lanjuan
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; Antibiotics. Antiinfectious agents. Antiparasitic agents; Bacterial Proteins - genetics; Biological and medical sciences; China - epidemiology; conjugation; Drug Resistance, Multiple, Bacterial - genetics; Escherichia coli - enzymology; Escherichia coli - genetics; Escherichia coli Infections - epidemiology; Escherichia coli Infections - microbiology; Escherichia coli Proteins - genetics; Genes, Bacterial - genetics; Genotype; Humans; Klebsiella Infections - epidemiology; Klebsiella Infections - microbiology; Klebsiella pneumoniae - enzymology; Klebsiella pneumoniae - genetics; Medical sciences; PFGE; Pharmacology. Drug treatments; Plasmids - genetics; Quinolones - pharmacology; Southern hybridization
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkn063

Objectives To characterize the prevalence of plasmid-mediated quinolone resistance determinants qnr and aac(6′)-Ib-cr in extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae. Methods qnrA, qnrB, qnrS, aac(6′)-Ib-cr and ESBL-encoding genes were detected by PCR. MICs of 10 antimicrobial agents were determined by Etest. PFGE was used to investigate the clonality of qnr- and aac(6′)-Ib-cr-producing isolates. Conjugation and Southern hybridizations were used to confirm whether qnr, aac(6′)-Ib-cr or ESBL-encoding genes were located on plasmids. Results Twenty-nine (8.0%) of 362 isolates were positive for qnr genes, and the qnrA-, qnrB- and qnrS-type genes were detected alone or in combination in 13 (3.6%), 8 (2.2%) and 9 (2.5%), respectively. Sixty-two (17.1%) isolates were positive for aac(6′)-Ib, of which 36 (9.9% of all) had the -cr variant. Conjugation and Southern hybridization revealed that qnrA, aac(6′)-Ib-cr and ESBL-encoding genes were always located on the same plasmids. Conclusions qnr and aac(6′)-Ib-cr genes were detected in 8.0% and 9.9% of ESBL-producing E. coli and K. pneumoniae, respectively. The plasmids carrying the qnr gene could be transferred by conjugation together with ESBL-encoding genes and aac(6′)-Ib-cr.