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 (19961998), 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.

James R. Johnson, Michael A. Kuskowski, Megan Menard, Abby Gajewski, Mariona Xercavins, and Javier Garau