Abstract:

【Objective】 The objective of the experiment was to determine the susceptibility of fluoroquinolones and the effect of active efflux pump in QnrS-positive animal clinical isolates of E. coli. 【Method】 The broth dilution method was used to determine MICs of fluoroquinolones against the QnrS-positive isolates. The accumulation of ciprofloxacin and the effect of efflux pump inhibitor,carbonyl cyanide m-chlorophenyl hydrazone (CCCP) for tested isolates of E. coli were measured by a fluorescenece method.【Result】 The susceptibility of QnrS-positive animal clinical isolates of E. coli to fluoroquinolone antibiotics varied greatly and decreased with energy dependence. The decrease in resistant isolates with QnrS was prominent. CCCP could increase the accumulation of ciprofloxacin in both the susceptible and the resistant strains of QnrS-positive isolates.However,the decrease of the latter was lower than the former. 【Conclusion】 The accumulation of ciprofloxacin in QnrS-positive animal clinical isolates of E. coli could be reduced and lower than the effective concentration by activating of active efflux pump,which affected the plasmid-mediated resistance.

Key words: Escherichia coli, Ciprofloxacin, active efflux pumps