Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2011
Publication Date: 2/9/2011
Citation: Jenkins, M., Fisher, D.S., Endale, D.M., Adams, P. 2011. Comparative die-off of Escherichia coli 0157:H7 and fecal indicator bacteria in pond water. Journal of Environmental Science and Technology. 45:1853-1858.
Interpretive Summary: The pathogenic strain of E. coli that is the cause of bloody diarrhea in humans and has been the cause of large-scale foodborne and waterborne illnesses is E. coli 0157:H7. Several researchers have reported on the persistence of this pathogen in surface waters of watersheds containing animal agriculture such as beef and dairy cattle, which are a principal source of E. coli 0157:H7. Researchers at the USDA-ARS J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA, designed experiments to compare the rates of die-off between a strain of E. coli 0157:H7 and fecal indicator bacteria generic E. coli and fecal enterococci. These experiments exposed the bacteria to natural sunlight, and filtered pond water (to remove microorganisms that are predators of bacteria) and unfiltered pond water. Die-off rates of the indicator bacteria were several times faster than the die-off rate of E. coli 0157:H7. Unlike the fecal indicator bacteria, E. coli 0157:H7 appeared to be resistant to the effects of solar UV-radiation, and predation from the pond water’s natural microbial community. The apparent resistance to solar radiation and microbial predation may account, in part, for the slower die-off rate of E. coli 0157:H7 compared to the indicator bacteria, and its persistence at infectious levels in surface water. The persistence of E. coli 0157:H7 in environmental surface waters enables it to be present in waters when the level of the indicator organisms is below the criterion of water impairment. This is important information for Environmental Protection Agencies.
Technical Abstract: In situ and in vitro experiments were designed to assess the effects of solar radiation and predation by indigenous microflora on the relative die-off rates of a toxogenic strain of Escherichia coli 0157:H7, commensal E. coli and fecal enterococci in surface waters from ponds in agricultural watersheds. The objective of these experiments was to discern a mechanism of persistence of E. coli 0157:H7 in surface waters compared to fecal indicator bacteria. Results of these experiments indicated that E. coli and fecal enterococci were affected by both insolation and apparent predation; whereas, E. coli 0157:H7 appeared to be resistant to both of these environmental stresses. The days to reach 99% die-off (T99-values) for E. coli 0157:H7 were significantly greater than the indicator bacteria. The capacity to prolong die-off maybe connected to the apparent persistence of E. coli 0157:H7 in surface waters, and may account for the lack of connection between the presence of E. coli 0157:H7 and the fecal indicator bacteria.