Detection of E. coli O157:H7 from house flies collected from animal production areas in California

House flies (Musca domestica) are commonly found in cattle feed lot operations and are known vectors of food-borne pathogens such as E. coli O157:H7, Shigella, and Campylobacter spp. The potential role that flies found in animal production areas could have in pathogen contamination of leafy greens is not well understood. Flies were collected from seven locations in California in leafy green production areas and cattle production facilities. Less than 1% of flies captured in the Salinas valley were positive when isolated on sorbitol MacConkey plates and later confirmed through a serological test. In contrast, 90% of the flies were positive for E. coli O157:H7 when polymerase chain reaction was conducted on pools of fly DNA. Primers sets used for detection were specific for the rfbE, fliC_h7, and stx1 genes. Disparity in the sensitivity of microbiological tests and that of molecular-based methods are evidence that standardized detection methods are needed. House flies are capable of carrying E. coli O157:H7, however their definitive importance in the transmission of food-borne pathogens to leafy greens still remains unclear.