JAC Advance Access originally published online on February 25, 2008
Journal of Antimicrobial Chemotherapy 2008 61(5):1003-1006; doi:10.1093/jac/dkn063
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Original research |
Plasmid-mediated quinolone resistance determinants qnr and aac(6')-Ib-cr in extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae in China
1 State Key Laboratory for Diagnosis and Treatment of Infectious Disease, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang 310003, China 2 James D. Watson Institute of Genome Sciences, Zhejiang University, Hangzhou, Zhejiang 310008, China 3 Beijing Genomics Institute, Chinese Academy of Sciences, Beijing 101300, China
Received 22 October 2007; returned 20 November 2007; revised 25 January 2008; accepted 26 January 2008
* Corresponding author: Tel: +86-571-8723-6421; Fax: +86-571-8723-6423; E-mail: yvys119{at}163.com
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.
Keywords: conjugation , PFGE , Southern hybridization
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