Escherichia coli O157:H7 is a foodborne pathogen that may be contracted by eating contaminated vegetables or undercooked contaminated beef products.1,2 Cattle are known reservoirs of this pathogen but it remains unclear how this pathogen is maintained in the environment.4,6 Infected cattle may defecate in farm ponds resulting in contamination of the pond water and may result in infection of its inhabitants.6 It has not been established whether amphibians can be infected by E. coli O157:H7 and perhaps serve as ‘spill-over’ hosts, or whether they may act as transport hosts upon metamorphosis. Therefore, we orally inoculated tadpole and metamorph American bullfrogs (Rana catesbeiana) with E. coli O157:H7 to determine their potential role as hosts for this pathogen.3 Tadpoles were housed in flow through systems and did not become infected; however, metamorphs were housed in stagnant systems and did become infected. These differences may be reflective of water system, developmental stage, or both. Stagnant water systems are likely more reflective of the farm pond system and offer greater opportunity for pathogen exposure than flowing systems. Additionally, stress is markedly increased in amphibians during metamorphosis as the larval immune system is disassembled to prepare for building of the adult immune system.5 Compromised immunity at this stage would support increased likelihood of infection by a pathogen. These data suggest that amphibians may play a role in the epidemiology of E. coli O157:H7 if exposed to contaminated water.
1. Centers for Disease Control and Prevention (CDC). 2006. Ongoing multistate outbreak of Escherichia coli serotype O157:H7 infections associated with consumption of fresh spinach—United States, September 2006. MMWR Morbid. Mortal. Wkly. Rep. 55:1045–46.
2. Food Safety and Inspection Service (FSIS). 2002. Guidance for Minimizing the Risk of Escherichia coli O157:H7 in Beef Slaughter Operations. 32 pp. Available from www.fsis.usda.gov.
3. Gray, M.J., S. Rajeev, D.L. Miller, A.C. Schmutzer, E.C. Burton, E. Rogers, and G. Hickling. 2007. Preliminary evidence that American bullfrogs (Rana catesbeiana) are suitable hosts for Escherichia coli O157:H7. Appl. Environ. Microbiol. (in press).
4. Ravva, S.V., and A. Korn. 2007. Extractable organic components and nutrients in wastewater from dairy lagoons influence the growth and survival of Escherichia coli O157:H7. Appl. Environ. Microbiol. 73: 2191–2198.
5. Rollins-Smith, L. 1998. Metamorphosis and the amphibian immune system. Immunol. Rev. 166:221–30.
6. Shere, J.A., C.W. Kaspar, K. J. Bartlett, S.E. Linden, B. Norell, S. Francey, D.M. Schaefer. 2002. Shedding of Escherichia coli O157:h7 in dairy cattle housed in a confined environment following waterborne inoculation. Appl. Environ. Microbiol. 68:1947–1954.