Emergence of fluoroquinolone-resistant Escherichia coli in fecal flora of cancer patients receiving norfloxacin prophylaxis

We studied 122 stool samples collected from 25 patients with hematologic malignancies who received prophylactic norfloxacin. Fecal samples were obtained at admission and twice weekly thereafter during prophylaxis. Fluoroquinolone-resistant Escherichia coli strains were isolated from the feces of 10 (40%) of the patients; two patients had fluoroquinolone-resistant E. coli strains prior to beginning norfloxacin treatment, and in the other eight patients, the strains appeared subsequently. One patient developed fluoroquinolone-resistant E. coli bacteremia after 10 days of norfloxacin administration.