Molecular epidemiology and evolution of resistance to quinolones in Escherichia coli after prolonged administration of ciprofloxacin in patients with prostatitis.

The emergence and evolution of quinolone-resistant Escherichia coli in faeces of patients with prostatitis treated with high-dose oral ciprofloxacin for 1 month were studied. In 11 of 23 patients, from whom only quinolone-susceptible E. coli was isolated before treatment, quinolone-resistant strains, genetically distinct from the quinolone-susceptible ones, predominated during and just after therapy. Two months after treatment, these were completely displaced by quinolone-susceptible E. coli, genetically distinct from the E. coli isolated before and during therapy. Hence, during ciprofloxacin therapy, half of the patients were transiently colonized with new, quinolone-resistant strains of E. coli.