Survival and Re-Growth of Enterococcus Mundtii in South Texas Agricultural Soils.

Surface water quality is routinely evaluated using the fecal indicator, enterococci. Recent results in south Texas suggest soil, rather than fecal material, may be a source of these bacteria, being transported to water through runoff following rainfall.  A series of laboratory experiments were conducted to evaluate the ability of enterococci to survive and re-grow in a common South Texas soil under a range of temperatures and moisture. Top soil samples of the Orelia series (fine-loamy, mixed, superactive, hyperthermic) were placed in small columns. Environmental and ATCC strains of Enterococcus mundtii, a species commonly isolated from both these soils and water, was used for the study. Experiments were set up using soil at several temperatures (40^o, 25^o, 10^oC) and moisture (dry or equivalent to 2.5 cm rainfall). Enterococci were enumerated using standard membrane filtration on selective media for Enterococcus spp. (mEI), following extraction from soil.  In non-autoclaved soil, at all three temperatures, there was initial growth only by the environmental strain; however, while numbers at 10^oC gradually decreased, at 40^oC there was little survival of either strain after three days. Growth in moist soil followed a similar pattern; however, the ATCC, as well as the environmental, strain, was able to grow rapidly at 10^oC before gradually decreasing over a three week period. Our studies suggest both moisture and temperature can significantly affect survival, growth and persistence of enterococci in a common south Texas agricultural soil and that the soil could potentially act as a reservoir for these bacteria in the environment.