In Extended Spectrum Beta-Iactamase (ESBI) producing Escherichia coli and Klebsiella pneumoniae strains, fluoroquinolone resistance is acquired mostly by target mutations in topoisomerase genes and increased expression of efflux pumps. ESBI positive 65 E. coli and 48 K pneumoniae strains isolated in Department of Microbiology and Clinical Microbiology, Faculty of Medicine, Ege University were investigated in this study. 58 E. coli and 21 K pneumoniae isolates displayed reduced susceptibility (intermediately-resistant or resistant) to ciprofloxacin or nalidixic acid by disc diffussion method. Ciprofloxacin, Phenyl-arginine-beta-naphthylamide (Phe-Arg-fi-naphthylamide-PfiNA) and nalidixic acid MIC values of these isolates were determined. The changes in nalidixic acid and ciprofloxacin MIC values in the presence of fixed concentration of PfiNA (20 pLg/ml) were investigated. Among 21 K.pneumoniae isolates, at least four fold reductions were observed in MIC values of ciprofloxacin, nalidixic acid and both for four, five and two isolates respectively. Among 58 E. coli isolates, at least four fold reductions were observed in MIC values of ciprofloxacin, nalidixic acid and both for eight, four and three isolates respectively. This result was evaluated to be indicative for presence of efflux pump mediated resistance in these isolates.

Keywords: Phe-Arg-ß-naphthylamide-PßNA, Efflux, Quinolone-resistance, E.coli, K.pneumoniae.