Fun in the Sun with Escherichia coli: Environmental Adaptation and Viability

Faculty Mentor(s)

Dr. Aaron Best and Dr. Michael Pikaart

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Bacteria of fecal origin present a health risk when present in bodies of water used for recreation. These organisms may be reduced in number when exposed to sun - a process known as insolation. The survivability of fecal indicator bacteria, specifically E. coli, of lab, environmental, and fecal isolates was examined. Bacterial cultures were made of all isolates then pipetted into polyethylene bags. The bags were placed outside in direct sunlight for up to three hours. Samples were removed from insolation in forty-five minute intervals and spread on plates to evaluate cell viability. E. coli counts decreased markedly with sun exposure and were completely inactivated after the full time period. There were clear differences in the survivability of each strain. The laboratory strain died most rapidly whereas the fecal isolates proved to be hardy and consistently decayed slower than most of the environmental isolates. These findings suggest that the environmental E. coli strains may not be better adapted to solar radiation than fecal isolates.

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