Isolation and characterization of pathogenic bacteria, including Escherichia coli O157: H7, from flies collected at a dairy farm field

Escherichia coli was isolated from the body surface, alimentary canal and excreta of the Musca domestica (Linnaeus), and the alimentary canal of Stomoxys calcitrans (Linnaeus) and Phaenicia sericata (Meigen) collected at a dairy farm in Tokushima Prefecture in 1997. We detected E. coli O157: H7 in the excreta and other pathogenic bacteria like Serratia marcescens, Enterobacter sakazakii and Pseudomonas fluorescens in the alimentary canal of M. domestica using the immunomagnetic separation method, polymerase chain reaction method and rapid identification kits. The isolated bacteria were resistant to more than three antibiotics. Escherichia coli O157: H7 from human and E. coli O157: H7 from M. domestica had similar susceptibility against tested antibiotics. These facts suggest that houseflies or other flies would be possible mechanical vectors to transmit the pathogens like enterohemorrhagic colitis or enteritis, although general sanitary conditions seem to be clearly improved in Japan. This is the first report of E. coli O157: H7 in the excreta of houseflies collected at a dairy farm field.