Epidemiological potential of excretion and regurgitation by Musca domestica (Diptera : Muscidae) in the dissemination of Escherichia coli O157 : H7 to food

We previously reported that enterohemorrhagic Escherichia coli O157: H7 (EH EC) proliferates in the mouthparts of the house fly Musca domestica vicina Macquart and are excreted for at least 3 d after ingestion. However, the ro le of the crop and excretory behavior of the house fly in contamination of human food with EHEC is not known. In the current experiments, EHEC persist ed in the crop of house flies for at least 4 d. The number of EHEC in an ex creted droplet was approximate to 10(4)' l h after bacterial feeding, >1.8 x 10(5) 3 h after feeding, and then drastically decreased after 24 h. Excre tion is one of the major mechanisms for decreasing number of EHEC in the cr op and gut of the house fly. The frequency of excretion by females with dev eloping eggs in their ovary was clearly higher (6.5 min per drop) than for males or females with mature eggs. Minute eosin-sign around a container fil led with eosin-supplemented trypticase soy broth might be derived from freq uent contact by house fly contaminated mouthparts. These results show that frequent excretion potentially enhances the dissemination of EHEC to foods, particularly during the first 24 h after ingestion of the bacteria.