Contribution of OqxAB Efflux Pump in Selection of Fluoroquinolone-Resistant .

The role of OqxAB efflux pump in was investigated in correlation with ciprofloxacin exposure. SE23 and SE191 were isolated from urinary tract infections and were analyzed in this study. Each carried resistance determinant and exhibited ciprofloxacin MIC of 0.06 and 0.5 mg/L, respectively. Tested strains were initially exposed to their ciprofloxacin MIC values for 24 hours. Later on, the ciprofloxacin exposition has been increased to a daily 1, 2, 4, and to a final 8 mg/L. Total cellular RNA was extracted at 30, 60, 90, and 120 minutes of initial exposure and after every 24 hours. Quantitative reverse-transcriptase PCR was performed from each RNA sample. Mutation in and genes was analyzed in each strain and multilocus sequence typing (MLST) was performed. Ciprofloxacin exposure selected resistant strain from SE191; by contrast, SE23 was not adjustable to the increasing ciprofloxacin concentrations. During initial exposure, both and expression remained low (2 = 1-2.03). However, increasing ciprofloxacin promoted expression as it reached fold increase of 15.8-22.8, while expression was maintained (2 = 2-2.15). An amino acid substitution Ser83Tyr in was detected in SE191, but no additional mutations occurred as consequence to ciprofloxacin exposure. MLST identified SE191 as ST274, while SE23 belonged to the novel ST2567. Ciprofloxacin concentration-dependent upregulation of efflux pump in is clonally related and contributes to selection for higher level of fluoroquinolone resistance.