Effects of temperature and sand on E. coil survival in a northern lake water microcosm.

A concern for public health officials is the presence of Escherichia coli (E. coli), an indicator of fecal contamination, in monitoring recreational waters. While E. coli is unlikely to cause disease in humans, its presence may indicate other more pathogenic microorganisms. Many factors can lead to changes in the survival of E. coli outside of the animal intestine and may affect the probability of colonizing a new host. Survival of bacteria in recreational water has been linked to water temperature, and most recently to the presence of sand on the beach. This project looked at the survival of an environmental E. coli isolate in lake water. Lake water microcosms were placed at 4, 10, 14, or 25 degrees C for up to 36 d and an enzyme-substrate test (Colisure, IDEXX Corp.) was used to determine the most probable number (MPN) of E. coli/100 ml water. E. coli numbers at all temperatures declined over the duration of the experiment. The decline was most pronounced at 14 degrees C and was slowest at 4 degrees C. The presence of sand in the microcosm increased the time that E. coli survived, regardless of temperature. From a beach management standpoint, these findings indicate that E.coli may persist in the environment in cooler water longer than in the warmer water encountered in late summer.