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Transfer of Escherichia coli O157:H7 to Spinach by House Flies, Musca domestica (Diptera: Muscidae)

April 2013 , Volume 103 , Number  4
Pages  373 - 380

Lakmini Wasala, Justin L. Talley, Udaya DeSilva, Jacqueline Fletcher, and Astri Wayadande

First, second, fourth, and fifth authors: Department of Entomology and Plant Pathology, and third author: Department of Animal Science, Oklahoma State University, Stillwater 74078.

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Accepted for publication 11 February 2013.

Filth flies are known mechanical vectors of pathogenic bacteria in hospital and restaurant settings, but their role as vectors for disseminating microbes to plants has not been demonstrated. Escherichia coli O157:H7 deposition by flies onto spinach was studied using molecular, microbiological, and microscopy techniques. Relative quantitative polymerase chain reaction studies showed that bacteria acquired by flies from contaminated cattle manure and deposited in regurgitation spots on leaves survived and multiplied. Scanning electron microscopy of the regurgitation spots of flies exposed to manure inoculated with E. coli suggested the multiplication of bacteria-like organisms within the spots. This finding implies that the bacteria were active and is consistent with a hypothesis that regurgitation spots serve as a nutrition source allowing E. coli O157:H7 to survive on the spinach phylloplane. E. coli O157:H7 persisted on fly body surfaces up to 13 days after exposure to acquisition sources, suggesting that fly cuticular surfaces are conducive to the growth of this pathogen. These results are consistent with the hypothesis of bioenhanced transmission of human pathogens by house flies and suggest that filth flies may affect the microbial safety of fresh produce.

© 2013 The American Phytopathological Society