| Abstract
| - BackgroundThe prevalence of fecal colonization with Escherichia coli that has reduced susceptibility to fluoroquinolones is unknown. A detailed characterization of such isolates is limited MethodsWe conducted 3 annual fecal surveillance initiatives at 2 hospitals from 2002 to 2004. All E. coli isolates with reduced susceptibility to fluoroquinolones (minimum inhibitory concentration [MIC] to levofloxacin, ⩾0.125 μg/mL) were identified. We characterized gyrA and parC mutations and organic solvent tolerance (OST). Isolates were compared using pulsed-field gel electrophoresis ResultsOf 789 fecal samples, 149 (18.9%) revealed E. coli with reduced susceptibility to fluoroquinolones. Of 149 isolates, 102 (68.5%) had a MIC ⩾8μg/mL, 138 (92.6%) had ⩾1 gyrA mutation, 101 (67.8%) had ⩾1 parC mutation, and 59 (39.6%) demonstrated OST. Isolates with a MIC ⩾8 versus <8 μg/mL had more target mutations (median, 3 vs. 1; P<.001) and more often exhibited OST (51% vs. 15%; P<.001). Of 149 isolates, 144 (96.6%) demonstrated a MIC ⩾16 μg/mL to nalidixic acid. The prevalence of OST differed across study years (P=.01). There was no clonal spread of isolates ConclusionsColonization by E. coli with reduced fluoroquinolone susceptibility is common, and fluoroquinolone-resistance characteristics differ significantly over time. Resistance to nalidixic acid may be useful in the identification of E. coli with early resistance mutations
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