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Antimicrobial Agents and Chemotherapy, April 2007, p. 1223-1227, Vol. 51, No. 4
0066-4804/07/$08.00+0     doi:10.1128/AAC.01195-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Prevalence of Plasmid-Mediated Quinolone Resistance Determinants QnrA, QnrB, and QnrS among Clinical Isolates of Enterobacter cloacae in a Taiwanese Hospital{triangledown}

Jiunn-Jong Wu,1 Wen-Chien Ko,2 Shu-Huei Tsai,3 and Jing-Jou Yan3,4*

Departments of Medical Laboratory Science and Biotechnology,1 Internal Medicine,2 Pathology, College of Medicine, National Cheng Kung University,3 Department of Pathology, National Cheng Kung University Hospital, Tainan, Taiwan, Republic of China4

Received 23 September 2006/ Returned for modification 11 December 2006/ Accepted 15 January 2007

The prevalence of three plasmid-mediated quinolone resistance determinants, QnrA, QnrB, and QnrS, among 526 nonreplicate clinical isolates of Enterobacter cloacae collected at a Taiwanese university hospital in 2004 was determined by PCR and colony hybridization, and the association of Qnr with the IMP-8 metallo-ß-lactamase was investigated. Eighty-six (16.3%) of all isolates were qnr positive, and the qnrA1-like, qnrB2-like, and qnrS1-like genes were detected alone or in combination in 3 (0.6%), 53 (10.1%), and 34 (6.5%) isolates, respectively. Among 149 putative extended-spectrum-ß-lactamase-producing isolates, 59 (39.6%) isolates, all of which were SHV-12 producers, harbored qnrA (0.7%; 1 isolate), qnrB (28.9%; 43 isolates), or qnrS (12.1%; 18 isolates). Forty-four (78.6%) of 56 IMP-8 producers carried qnrB (58.9%; 33 isolates), qnrS (25.0%; 14 isolates), or both. PCR and sequence analysis revealed that qnrA1 was located in a complex sul1-type integron that contains dhr15, aadA2, qacE{Delta}1, sul1, orf513, qnrA1, ampR, and qacE{Delta}1. Conjugation experiments revealed the coexistence of qnrB and blaIMP-8 on the transferred plasmids and the absence of ß-lactamase content on the transferred qnrS-positive plasmids. The transferred blaIMP-8-positive plasmids with and without qnrB had very similar restriction patterns, suggesting the horizontal mobility of qnrB. Pulsed-field gel electrophoresis showed six major patterns among the 44 qnr-positive IMP-8-producing isolates. Thus, the extremely high prevalence of qnr among the metallo-ß-lactamase-producing E. cloacae isolates in the hospital may be due mainly to the intrahospital spread of a few clones and the dissemination of plasmids containing both qnrB and blaIMP-8.

* Corresponding author. Mailing address: Department of Pathology, National Cheng Kung University Hospital, 138 Sheng-Li Road, Tainan 70428, Taiwan, Republic of China. Phone: 886-6-2353535, ext. 2634. Fax: 886-6-2766195. E-mail: jingjou{at}mail.ncku.edu.tw

{triangledown} Published ahead of print on 22 January 2007.

Antimicrobial Agents and Chemotherapy, April 2007, p. 1223-1227, Vol. 51, No. 4
0066-4804/07/$08.00+0     doi:10.1128/AAC.01195-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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