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Antimicrobial Agents and Chemotherapy, May 2009, p. 1892-1897, Vol. 53, No. 5
0066-4804/09/$08.00+0     doi:10.1128/AAC.01400-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

New Plasmid-Mediated Quinolone Resistance Gene, qnrC, Found in a Clinical Isolate of Proteus mirabilis{triangledown}

Minghua Wang,1,{dagger} Qinglan Guo,1,{dagger} Xiaogang Xu,1 Xiaoying Wang,1 Xinyu Ye,1 Shi Wu,1 David C. Hooper,2 and Minggui Wang1,3*

Institute of Antibiotics, Huashan Hospital,1 Institute of Biomedical Sciences, Fudan University, Shanghai 200040, China,3 Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts2

Received 18 October 2008/ Returned for modification 10 January 2009/ Accepted 22 February 2009

Since the discovery of qnrA in 1998, two additional qnr genes, qnrB and qnrS, have been described. These three plasmid-mediated genes contribute to quinolone resistance in gram-negative pathogens worldwide. A clinical strain of Proteus mirabilis was isolated from an outpatient with a urinary tract infection and was susceptible to most antimicrobials but resistant to ampicillin, sulfamethoxazole, and trimethoprim. Plasmid pHS10, harbored by this strain, was transferred to azide-resistant Escherichia coli J53 by conjugation. A transconjugant with pHS10 had low-level quinolone resistance but was negative by PCR for the known qnr genes, aac(6')-Ib-cr and qepA. The ciprofloxacin MIC for the clinical strain and a J53/pHS10 transconjugant was 0.25 µg/ml, representing an increase of 32-fold relative to that for the recipient, J53. The plasmid was digested with HindIII, and a 4.4-kb DNA fragment containing the new gene was cloned into pUC18 and transformed into E. coli TOP10. Sequencing showed that the responsible 666-bp gene, designated qnrC, encoded a 221-amino-acid protein, QnrC, which shared 64%, 42%, 59%, and 43% amino acid identity with QnrA1, QnrB1, QnrS1, and QnrD, respectively. Upstream of qnrC there existed a new IS3 family insertion sequence, ISPmi1, which encoded a frameshifted transposase. qnrC could not be detected by PCR, however, in 2,020 strains of Enterobacteriaceae. A new quinolone resistance gene, qnrC, was thus characterized from plasmid pHS10 carried by a clinical isolate of P. mirabilis.

* Corresponding author. Mailing address: Institute of Antibiotics, Huashan Hospital, Fudan University, 12 M. Wulumuqi Rd., Shanghai 200040, People's Republic of China. Phone: (86-21)-52888195. Fax: (86-21)-62488290. E-mail: mgwang{at}fudan.edu.cn

{triangledown} Published ahead of print on 2 March 2009.

{dagger} M.W. and Q.G. contributed equally to this work.

Antimicrobial Agents and Chemotherapy, May 2009, p. 1892-1897, Vol. 53, No. 5
0066-4804/09/$08.00+0     doi:10.1128/AAC.01400-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



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