[Resistant mutant prevention concentration of fluoroquinolones in clinical isolates of extended spectrum beta-lactamase (ESBL) producing and non-producing strains of Escherichia coli].

The aim of this job is to study the capacity of ciprofloxacin and levofloxacin in restricting the development of resistant mutants in strains of Escherichia coli by determining the mutant prevention concentration (MPC). Ninety-nine isolates of E. coli with different fluoroquinolone susceptibilities were studied and divided into ESBL-producing (n = 60) and non-ESBL producing (n = 36) groups. MPC values were determined using an inoculum of 1010 cfu/ml on Mueller-Hinton plates with serial dilutions of the antibiotics. No significative differences were detected in MIC of ESBL-producing and non-ESBL producing strains of E. coli. Ciprofloxacin susceptible ESBL-producing strains exhibit higher MPC for ciprofloxacin and levofloxacin than non-ESBL producing strains. Our study helps to explain the frequent fluoroquinolone resistance found in ESBL-producing strains. In this context, doubts emerge about the advisability of using fluoroquinolones to treat infections caused by ESBL-producing strains.