PROLONGED SURVIVAL OF AN ENVIRONMENTAL ESCHERICHIA-COLI IN LABORATORY SOIL MICROCOSMS

The survival, persistence, and dispersal of bacteria in soil raises serious water quality questions for rural areas of the world especially where podzol-type soils dominate. To determine survival characteristics of an environmentally derived multiple-antibiotic resistant E coli, it was added to laboratory containers containing sandy-loam podzol soils taken from two different locations ('Webb', pH 6.8-8.3 and 'Rich', pH 5.5-7.2). This was done in order to study the stability of the tracer bacterium under conditions designed to mimic those that might be encountered during subsequent field mini-plot studies. Sets of microcosms consisting of three replicates of each soil received 10(12) or 10(13) colony forming units per g of soil and were incubated at four temperatures (5, 10, 20, and 37-degrees-C) and two moisture levels (15% i.e. average field capacity and saturation) for 160 days. The microcosm data gave estimated maximum survical times for the 'Webb' soil of 23.3 months at 5-degrees-C under saturating moisture conditions and 20.7 months for the 'Rich' soil under the same conditions using exponential regression analysis of the data.