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Antimicrobial Agents and Chemotherapy, May 2001, p. 1515-1521, Vol. 45, No. 5
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.5.1515-1521.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Genetic Characterization of Highly Fluoroquinolone-Resistant Clinical Escherichia coli Strains from China: Role of acrR Mutations

Hui Wang,1 Joann L. Dzink-Fox,2 Minjun Chen,1 and Stuart B. Levy2,3,*

Department of Clinical Laboratory, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, Beijing 100730, People's Republic of China,1 and Center for Adaptation Genetics and Drug Resistance and the Departments of Molecular Biology and Microbiology2 and of Medicine,3 Tufts University School of Medicine, Boston, Massachusetts 02111

Received 3 November 2000/Returned for modification 12 January 2001/Accepted 16 February 2001

The genetic basis for fluoroquinolone resistance was examined in 30 high-level fluoroquinolone-resistant Escherichia coli clinical isolates from Beijing, China. Each strain also demonstrated resistance to a variety of other antibiotics. PCR sequence analysis of the quinolone resistance-determining region of the topoisomerase genes (gyrA/B, parC) revealed three to five mutations known to be associated with fluoroquinolone resistance. Western blot analysis failed to demonstrate overexpression of MarA, and Northern blot analysis did not detect overexpression of soxS RNA in any of the clinical strains. The AcrA protein of the AcrAB multidrug efflux pump was overexpressed in 19 of 30 strains of E. coli tested, and all 19 strains were tolerant to organic solvents. PCR amplification of the complete acrR (regulator/repressor) gene of eight isolates revealed amino acid changes in four isolates, a 9-bp deletion in another, and a 22-bp duplication in a sixth strain. Complementation with a plasmid-borne wild-type acrR gene reduced the level of AcrA in the mutants and partially restored antibiotic susceptibility 1.5- to 6-fold. This study shows that mutations in acrR are an additional genetic basis for fluoroquinolone resistance.

* Corresponding author. Mailing address: Center for Adaptation Genetics and Drug Resistance, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6764. Fax: (617) 636-0458. E-mail: slevy{at}opal.tufts.edu.

Antimicrobial Agents and Chemotherapy, May 2001, p. 1515-1521, Vol. 45, No. 5
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.5.1515-1521.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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