Contribution of mutation at amino acid 45 of AcrR to acrB expression and ciprofloxacin resistance in clinical and veterinary Escherichia coli isolates.

Fluoroquinolone-resistant Escherichia coli isolates which overexpressed acrB and had a substitution at amino acid 45 of AcrR were complemented with wild-type acrR. Complementation led to increased sensitivity to ciprofloxacin and to ethidium bromide, suggesting that mutation at amino acid 45 of AcrR contributes to ciprofloxacin resistance.