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Antimicrobial Agents and Chemotherapy, May 2001, p. 1467-1472, Vol. 45, No. 5
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.5.1467-1472.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Enhanced Expression of the Multidrug Efflux Pumps AcrAB and AcrEF Associated with Insertion Element Transposition in Escherichia coli Mutants Selected with a Fluoroquinolone

A. S. Jellen-Ritter and W. V. Kern*

Section of Infectious Diseases and Clinical Immunology, Department of Medicine, University Hospital and Medical Center, D-89070 Ulm, Germany

Received 16 August 2000/Returned for modification 18 November 2000/Accepted 23 February 2001

The development of fluoroquinolone resistance in Escherichia coli may be associated with mutations in regulatory gene loci such as marRAB that lead to increased multidrug efflux, presumably through activation of expression of the AcrAB multidrug efflux pump. We found that multidrug-resistant (MDR) phenotypes with enhanced efflux can also be selected by fluoroquinolones from marRAB- or acrAB-inactivated E. coli K-12 strains having a single mutation in the quinolone-resistance-determining region of gyrA. Mutant 3-AG100MKX, obtained from a mar knockout strain after two selection steps, showed enhanced expression of acrB in a reverse transcriptase PCR associated with insertion of IS186 into the AcrAB repressor gene acrR. In vitro selection experiments with acrAB knockout strains yielded MDR mutants after a single step. Enhanced efflux in these mutants was due to increased expression of acrEF and associated with insertion of IS2 into the upstream region of acrEF, presumably creating a hybrid promoter. These observations confirm the importance of efflux-associated nontarget gene mutations and indicate that transposition of genetic elements may have a role in the development of fluoroquinolone resistance in E. coli.

* Corresponding author. Mailing address: Medizinische Universitätsklinik und Poliklinik, D-89070 Ulm, Germany. Phone: 49-731-502 4423. Fax: 49-731-502 4488. E-mail: winfried.kern{at}medizin.uni-ulm.de.

Antimicrobial Agents and Chemotherapy, May 2001, p. 1467-1472, Vol. 45, No. 5
0066-4804/01/$04.00+0   DOI: 10.1128/AAC.45.5.1467-1472.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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