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Use of bioluminescent Escherichia coli to determine retention during the life cycle of the housefly, Musca domestica (Diptera: Muscidae, L)

Schuster, Greta L., Donaldson, Janet R., Buntyn, Joe O., Duoss, Heather A., Callaway, Todd R., Carroll, Jeff A., Falkenberg, Shollie M., Schmidt, Ty B.
Musca domestica, adults, cattle, cattle manure, disease transmission, enterohemorrhagic Escherichia coli, enteropathogenic Escherichia coli, environmental exposure, ingestion, insect vectors, larvae, metamorphosis, pupae, viability
Researchers have documented that the housefly (Musca domestica) can serve as a vector for the spread of foodborne pathogens to livestock, food, and humans. Most studies have investigated Musca domestica as a vector only after the fly comes into contact or consumes the pathogen as an adult. The objective of this study was to determine whether the larvae of Musca domestica could ingest Escherichia coli from bovine manure and whether the E. coli could survive the metamorphosis process and be transmitted. Larvae (n = 960) were incubated in sterilized bovine manure inoculated with 0, 3, 5, and 8 log10 colony-forming units (CFU)/mL of bioluminescent E. coli for 24 (larvae stage), 48 (larvae stage), 120 (pupae stage), and 192 h (adult stage). Larvae incubated for 24 h in bovine manure possessed 0.0, 2.7, 2.9, and 3.5 log10 CFU/mL of E. coli, from inoculated with 0, 3, 5, and 8 log10 CFU/mL of E. coli, respectively. Concentrations of E. coli within the pupae were 0.0, 1.7, 1.9, and 2.2 log10 CFU/mL for each inoculation concentration, respectively. Flies that emerged from the pupae stage contained 0.0, 1.3, 2.2, and 1.7 log10 CFU/mL of E. coli from larvae incubated in manure inoculated with concentrations of E. coli, respectively. These results suggest the housefly can emerge with quantities of E. coli. While this was an enteropathogenic E. coli (EPEC), these data may suggest that if the fly is capable of retaining similar concentrations of an enterohemorrhagic E. coli (EHEC), these concentrations may be capable of initiating illness in humans. Furthermore, the E. coli concentration within and on adult flies is related to environmental exposure. It must be noted that larvae were incubated in sterilized bovine manure, and there was no other bacterial competition for the E. coli. Thus, the rate of positive flies and concentrations present when flies emerged may vary under more realistic conditions.