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JAC Advance Access originally published online on October 5, 2006
Journal of Antimicrobial Chemotherapy 2006 58(6):1154-1159; doi:10.1093/jac/dkl412
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Role of the CmeABC efflux pump in the emergence of fluoroquinolone-resistant Campylobacter under selection pressure

Meiguan Yan, Orhan Sahin, Jun Lin{dagger} and Qijing Zhang*

Department of Veterinary Microbiology and Preventive Medicine, College of Veterinary Medicine Iowa State University, Ames, IA 50011, USA

Received 23 June 2006; returned 7 August 2006; revised 14 September 2006; accepted 14 September 2006

*Corresponding author. Tel: +1-515-294-2038; Fax: +1-515-294-8500; E-mail: zhang123{at}iastate.edu

Objectives: The objective of this study was to determine the contribution of the CmeABC efflux pump to the emergence of fluoroquinolone (FQ)-resistant mutants in Campylobacter jejuni under various levels of selection pressure.

Methods: The frequency of emergence of ciprofloxacin-resistant mutants was measured in wild-type C. jejuni NCTC 11168 and its isogenic cmeB mutant and cmeR mutant (overexpressing cmeABC) using plates containing various concentrations of ciprofloxacin. Representative ciprofloxacin-resistant mutants were selected for gyrA sequence analysis and MIC determination. Accumulation of ciprofloxacin in Campylobacter cells was measured using spectrofluorometry.

Results: Mutation of cmeB drastically reduced the frequency of emergence of FQ-resistant mutants at 10x and 32x the MIC of ciprofloxacin, while the cmeR mutant displayed an approximately 17-fold increase in the frequency of emergence of the mutants at 32x the MIC when compared with the wild-type strain. Various point mutations occurred in gyrA in the FQ-resistant mutants selected at 5x and 10x the MIC, while the Thr-86->Ile mutation was predominant in the mutants selected at 32x the MIC. The Thr-86->Ile change conferred a high-level resistance to FQs, but other mutations only conferred an intermediate-level FQ resistance. In contrast, all types of gyrA mutations in the CmeABC-overexpressed background conferred high-level resistance to ciprofloxacin. Overexpression of cmeABC significantly reduced the amount of ciprofloxacin accumulated within bacterial cells.

Conclusions: CmeABC is not only important for maintaining high-level resistance to FQs but also contributes significantly to the emergence of FQ-resistant mutants. Inhibition of this efflux pump may prevent the emergence of clinically relevant FQ-resistant Campylobacter mutants.

Keywords: ciprofloxacin , gyrA mutations , efflux , antibiotic resistance


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