June 21, 2007 For the first time researchers have identified American bullfrogs as potentially suitable hosts for E. coli O157:H7, a common source of food-borne illness. Escherichia coli O157:H7 is a major food safety concern worldwide.
Cattle are known reservoirs of the bacterium and researchers are now suggesting transmission to aquatic vertebrates, such as amphibians, occurs when infected cattle defecate in water sources. Infected tadpoles could then shed the pathogen and infect cattle drinking the contaminated water as well as vegetables if the water is used for irrigation.
In the study researchers orally inoculated American bullfrog tadpoles and metamorphs with E. coli O157:H7 and tested for infection after 14 days. Tadpoles, which were housed in flowthrough aquaria, did not become infected, however 54% of metamorphs tested positive after being housed in stagnant aquaria.
"Our results suggest that American bullfrog metamorphs could function as a 'spill-over' reservoir for E. coli O157:H7 and thus contribute to its persistence in aquatic environments," say the researchers. "Further, given that metamorphs are capable of dispersal, they may have a role in the epidemiology of this pathogen."
They report their findings in the June 2007 issue of the journal Applied and Environmental Microbiology. (M.J. Gray, S. Rajeev, D.L. Miller, A.C. Schmutzer, E.C. Burton, E.D. Rogers, G.J. Hickling. 2007. Preliminary evidence that American bullfrogs (Rana catesbeiana) are suitable hosts for Escherichia coli O157:H7. Applied and Environmental Microbiology, 73. 12: 4066-4068).
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