Environmental factors affecting Escherichia coli and Salmonella typhimurium numbers on land used for effluent disposal

Abstract

Escherichia coli cells applied to soil and pasture in piggery effluent, or as a bacteria in water suspension, were found to be susceptible to desiccation in grey clay loam soil when the soil dry matter exceeded 90%, the approximate wilting point of this soil. Inoculation of the cells onto dry soil resulted in c. 99% reduction in cell numbers in 24 hr, even when the soil was shaded. Surviving cells were observed to persist for 8 weeks after inoculation. Salmonella typhimurium cell suspensions added to experimental plots displayed similar persistence characteristics to E. coli. E. coli cells in effluent or suspensions added to moist soil did not exhibit a rapid initial decline in number. The number of E. coli on the pasture diminished quickly even when the soil below was moist. Only a small percentage of inoculum cells were collected in run-off water from the plots after heavy rainfall, although the absolute number of cells was sufficient to pollute a large volume of water if discharged directly into a watercourse.