An estimated 73,000 human cases of E. coli O157:H7 infection occur each year in the United States, resulting in 61 deaths on average (1). Cattle are known reservoirs of E. coli O157:H7, and there is considerable effort by the food safety industry to minimize its prevalence in herds (2,3). Infected cattle may defecate in water sources (such as farm ponds and streams), resulting in transmission to herd members (4). Moreover, it is possible that aquatic vertebrates that inhabit watersheds become infected, and serve as a ‘spill-over’ reservoir (5). Tadpoles are prime candidates for spill-over hosts of zoonotic pathogens, because they scavenge on aquatic macrophytes and benthos (6), and incidentally ingest microorganisms (7). Pathogenic microorganisms, such as E. coli O157:H7, may infect the intestines or other organs of tadpoles. If this is true, tadpoles could shed viable E. coli O157:H7 and function as a source of infection for cattle that drink contaminated water. Additionally, water contaminated by infected tadpoles could potentially serve as a source of fruit and vegetable contamination if water is used for irrigation. Inasmuch as tadpole densities can exceed 100 individuals m-2, they excrete copious amounts of feces, and some species develop for more than 12 months resulting in overlapping cohorts and continuous presence (8), this vertebrate group could contribute significantly to maintaining E. coli O157:H7 in aquatic environments.
In 2006, Gray et al. (9) orally inoculated American bullfrog metamorphs and tadpoles with E. coli O157:H7, and determined that this species was a suitable host. However, infection by oral inoculation of a pathogen does not necessarily imply that the host could be naturally infected. To date, natural infection of amphibians by a zoonotic pathogen via exposure to cattle feces containing an environmentally relevant concentration of the pathogen has not been tested. These data are fundamental to understanding the threat of American bullfrogs as sources of E. coli O157:H7 in the environment.
The objective of this study is:
Quantify infection rates in American bullfrog tadpoles exposed to cattle feces inoculated with E. coli O157:H7 in outdoor aquatic mesocosms that simulate a natural environment.
Collaborators: UT East Tennessee Research and Education Center, UT Departments of Animal Science and Forestry, Wildlife and Fisheries, Tennessee Agricultural Experiment Station, University of Georgia College of Veterinary Medicine
(1) Centers for Disease Control and Prevention (CDC). 2006. Escherichia coli O157:H7.
(2) Center for Disease Control and Prevention (CDC) Foundation. 2006. Get Smart on the Farm Campaign. http://www.cdc.gov/narms/get_smart.htm.
(3) Looper, M. L., T. S. Edrington, R. Rores, C. F. Rosenkrans Jr, M. E. Nihsen, and G. E. Aiken. 2006. Prevalence of Escherichia coli O157:H7 and Salmonella in beef steers consuming different forage diets. Lett. Appl. Microbiol. 42:583-88.
(4) Shere, J. A., C. W. Kaspar, K. J. Bartlett, S. E. Linden, B. Norell, S. Francey, and D. M. Schaefer. 2002. Shedding of Escherichia coli O157:h7 in dairy cattle housed in a confined environment following waterborne inoculation. Appl. Environ. Microbiol. 68:1947-54
(5) Daszak, P., A. A. Cunningham, and A. D. Hyatt. 2000. Emerging infectious diseases of wildlife—threats to biodiversity and human health. Science 287:443-49.
(6) Hoff, KvS, AR Blaustein, RW McDiarmid and R
Altig. 1999. Behavior. Pp 215-239. In: McDiarmid, RW and R
Altig (eds), Tadpoles. The Biology of Anuran Larvae. The
(7) Seale, D. B., K. Hoff, and R. Wassersug. 1979. Xenopus laevis larvae as model suspension feeders. Hydrobiologia 87:161-169.
(8) Alford RA.
1999. Ecology: resource use,
competition, and predation. Pages
240-278 in RW McDiarmid and R Altig (eds).
Tadpoles: the biology of anuran larvae.
(9) Gray MJ, S Rajeev, DL Miller, AC Schmutzer, EC Buron, ED Rogers, GJ Hickling. 2007. Preliminary evidence that American bullfrogs (Rana catesbeiana) are suitable hosts for Escherichia coli O157:H7. Applied and Environmental Microbiology 73:4066–4068.
I grew up in Swanton, a small town in northwestern Vermont. I completed my undergraduate studies at Castleton State College, double majoring in Biology and Health Science with a minor in Chemistry. While at Castleton, I studied the survivability of Escherichia coli O157:H7 in pond water. This project focused on how seasonal temperatures and cattle access influence the survivability of the bacteria in pond water. Furthermore, I served as the president of the Sigma Zeta National Science and Mathematics Honor Society and the Student Science Association. I was a member of the varsity ice hockey team at Castleton as well. My future goals include the pursuit of an MD/PhD. When I’m not busy with work or school, I enjoy time with my daughter, playing hockey, running, hiking, hunting and fishing.
Phone: (865) 974-3897