Similarity between human and chicken Escherichia coli isolates in relation to ciprofloxacin resistance status

Background. The food supply is suspected to be a source of fluoroquinolone-resistant Escherichia coli that cause disease in humans, but supporting molecular data are lacking. Methods. We performed a molecular-epidemiological comparison, in Barcelona, Spain (1996-1998), of 117 contemporaneous, geographically matched E. coli isolates from humans (35 blood isolates and 33 fecal) or chickens (49 fecal) that were either susceptible (n = 57) or resistant (n = 60) to ciprofloxacin and analyzed them by phylogenetic group, virulence genotype, and O antigens using random amplified polymorphic DNA (RAPD) analysis and pulsed-field gel electrophoresis (PFGE). Results. When analyzed by phylogenetic distribution, virulence profiles, and O antigens, resistant human isolates were distinct from susceptible human isolates but were largely indistinguishable from chicken isolates, whereas resistant and susceptible chicken isolates were similar. Susceptible human isolates contained more virulence-associated genes and more frequently expressed virulence-associated O antigens than did resistant human or any chicken isolates. Certain resistant human isolates closely resembled chicken isolates by RAPD and PFGE analysis. Conclusions. Ciprofloxacin-resistant E. coli may arise de novo in poultry from susceptible progenitors, be transmitted to humans via the food supply, and go on to cause potentially life-threatening infections. If confirmed, these findings would mandate efforts to eliminate this reservoir of drug-resistant pathogens and/or to block their transmission to humans.