Colonization and infection with fluoroquinolone-resistant Escherichia coli among cancer patients: clonal analysis.

Escherichia coli with high-level fluoroquinolone resistance were isolated from feces and/or various body sites of 16 cancer patients who were on oral fluoroquinolone prophylaxis. Population analysis of fecal isolates in 11 patients showed that fluoroquinolone-resistant E. coli was the only aerobic gram-negative bacillus present and exhibited a relatively homogenous fluoroquinolone MIC distribution. Molecular typing by pulsed field gel electrophoresis of chromosomal DNA digests or by random amplified polymorphic DNA fingerprinting confirmed the clonal nature of gastrointestinal tract colonization with E. coli. Genotyping of ten colonies picked from the same fecal culture demonstrated identical strains in four of four patients examined. Identical genotypes from the same patient were isolated over prolonged periods of time in 12 of 12 cases examined, with one patient (with the longest follow-up of 14 months) who lost his initial genotype and became persistently colonized with a new genotype. In the 11 patients who developed infection due to fluoroquinolone-resistant E. coli, molecular typing also indicated that fecal colonization was associated with, and presumably preceded infection due to an indistinguishable genotype of fluoroquinolone-resistant E. coli.