The frequency of in vitro resistance to fluoroquinolones among clinical isolates of Escherichia coli

The aim of this study was to investigate the activity of new quinolones against clinical isolates of E. coli, obtained from hospitalized patients between 1999-2000, in Eastern Romania. We tested 411 strains, isolated from urine. Susceptibility of the isolates to norfloxacin, ciprofloxacin, nalidixic acid and ofloxacin was performed using the dilution method in Mueller-Hinton agar. Susceptibility was reported using the NCCLS breakpoints. Minimum inhibitory concentration (MIC) was defined as the lowest concentration of antimicrobials that inhibited growth of the bacteria. Based on MIC breakpoints for defining susceptibility, between 12.4-13.7% of isolates were resistant to modern quinolones. Resistance to nalidixic acid significantly diminished the clinical use: level of the susceptible strains was only 12.9%.