Antimicrobial-resistant and extraintestinal pathogenic Escherichia coli in retail foods

Background. Extraintestinal Escherichia coli infections are associated with specialized extraintestinal pathogenic E. coli (ExPEC) strains and, increasingly, with antimicrobial resistance. The food supply may disseminate ExPEC and antimicrobial-resistant E. coli. Methods. In a prospective survey of 1648 diverse food items from 10 retail markets in the Minneapolis-St. Paul area during 2001-2003, selective cultures and disk-diffusion assays for the isolation and characterization of antimicrobial-resistant E. coli and polymerase chain reaction-based assays and O serotyping to define ExPEC-associated traits were performed. Results. E. coli contamination exhibited a prevalence gradient from miscellaneous foods (9%), through beef or pork (69%), to poultry (92%; P<.001). Among E. coli-positive samples, similar prevalence gradients were detected for antimicrobial resistance (27%, 85%, and 94% of samples, respectively; P<.001 ) and ExPEC contamination (4%, 19%, and 46%, respectively; P<.001). By multivariate analysis, beef or pork and poultry from natural-food stores exhibited reduced risks of E. coli contamination and antimicrobial resistance. Indirect evidence suggested on-farm selection of resistance. Four food-source ExPEC isolates (from pea pods, turkey parts, ground pork, and vegetable dip) closely resembled selected human clinical isolates by O antigen and genomic profile. Conclusions. Retail foods may be an important vehicle for community-wide dissemination of antimicrobial-resistant E. coli and ExPEC, which may represent a newly recognized group of medically significant foodborne pathogens.