Effect of AcrAB Efflux Pump on Ciprofloxacin Resistance Rate in Escherichia coli Isolates

One of the important mechanisms of resistance to fluoroquinolones in Escherichia coli, is AcrAB efflux pumps activity. In this study, the frequency of acrA and acrB genes and the effect of efflux pumps on the ciprofloxacin resistance in isolates of extended-spectrum beta-lactamase (ESBL) producing E. coli, were investigated.
This experimental study was performed on 66 ESBL producing E.­coli strains isolated from urine sample of outpatients referred to two medical centers in Kermanshah city. Antibiotic susceptibility of the isolates to 10 common antibiotics, was assessed using standard disk diffusion method (according to the CLSI guideline). The acrA and acrB genes were detected by PCR in ciprofloxacin resistant isolates. The inhibitory effect of bacterial efflux pump (carbonyl cyanide m-chlorophenyl hydrazone (CCCP), with final concentration of 25μg/ml on MIC of the ciprofloxacin resistant isolates, was assessed using agar dilution method. The data were analyzed using Chi-square test.
Out of 66 isolates, 45 isolates (68.1%), were resistant to ciprofloxacin. Both acrA and acrB genes, were found in the ciprofloxacin resistant E. coli isolates. The effect of CCCP on the resistance of isolates to ciprofloxacin led to the decrease in MIC only in 7 isolates (15.5%).
The results of this study showed that despite the high resistance to ciprofloxacin and the presence of both acrA and acrB genes in most of the E.coli isolats, the efflux pump activity exists in a small percentage of isolates. Therefore, efflux pumps play a small role in ciprofloxacin resistance in E. coli.