Molecular Analysis of Antimicrobial-Susceptible and -Resistant Escherichia coli from Retail Meats and Human Stool and Clinical Specimens in a Rural Community Setting

Background: Foodborne antimicrobial-resistant Escherichia coli may colonize and cause infections in humans, but definitive proof is elusive and supportive evidence is limited. Methods: Approximately contemporaneous antimicrobial-resistant (n=181) and antimicrobial-susceptible (n=159) E. coli isolates from retail meats and from human stool and clinical specimens from a single rural U. S. community were compared for polymerase chain reaction (PCR)-defined phylogenetic group (A, B1, B2, or D) and virulence genotype. Meat and human isolates from the same phylogenetic group with similar virulence profiles underwent sequential two-locus sequence analysis, random amplified polymorphic DNA ( RAPD) analysis, and pulsed-field gel electrophoresis (PFGE) analysis. Results: According to phylogenetic distribution, resistant stool isolates were more similar to resistant meat isolates than to susceptible stool isolates. Overall, 19% of meat isolates satisfied molecular criteria for extraintestinal pathogenic E. coli (ExPEC). Nine sequence groups included meat and human isolates, and 17 of these 64 isolates demonstrated >80% RAPD profile similarity to an isolate from the alternate source group ( meat vs. human). However, PFGE profiles of the 17 isolates were unique, excepting two stool isolates from the same household. Conclusion: Nearly 20% of meat-source resistant E. coli represented ExPEC. The observed molecular similarity of certain meat and human-source E. coli isolates, including antimicrobial-resistant and potentially pathogenic strains, supports possible foodborne transmission.