Objective: To investigate multiple-antibiotic-resistance mechanism in clinical strains of Escherichia coli.
Methods: Accumulation of ciprofloxacin in clinical isolates of Escherichia coli was measured by fluorometry, and acrAB gene was identified by PCR and Southern blot. The levels of acrAB gene expression were measured by RT-PCR. DNA fragments were sequenced by automated fluorescence sequencing.
Results: The state concentration of ciprofloxacin in multiple-antibiotic-resistant (Mar) strains was significantly lower than that in susceptible stsains (0.73 mg/L +/- 0.04 mg/L vs 2.00 mg/L +/- 0.07 mg/L A(660), P < 0.001). The level of acrAB gene expression in Mar strains was significantly higher than that in other strains. No deletion or point mutation in acrAB gene were found in Mar and susceptible clinical Escherichia coli isolates.
Conclusions: High expression of acrAB gene leads to multiple-antibiotic-resistance in clinical strains of Escherichia coli, and Mar operon may contribute to the regulation of acrAB gene expression.