Survival of Escherichia coli in a field amended with cow feces slurry

Abstract

Survival of Escherichia coli in soil was examined. In a laboratory microcosm experiment, survival of a single E. coli strain inoculated in soil was examined under two soil moisture regimes. Plate counting with a selective medium showed that the number of E. coli decreased faster under dry soil conditions than under moist ones, and survived more than 1 month under both conditions. In field experiments conducted both in the summer and winter seasons, cow feces slurry was applied to experimental fields and soils were sampled periodically for CFU determination. As a result, it was shown that E. coli derived from cow feces slurry survived at least several months, and that they could move downward and contaminate the subsoil. When the contaminated soil samples collected from the field experiments were kept overnight at 37°C, CFU of the E. coli increased in most of the cases tested. In four cases, E. coli were detected only after the incubation. These results suggested the importance of appropriate treatment of animal feces to reduce the number of contaminating bacteria before application to agricultural fields.