Comparative persistence of Salmonella and Escherichia coli O157:H7 in loam or sandy loam soil amended with bovine or swine manure

The fate of Salmonella and Escherichia coli O157:H7 in swine or dairy manure amended into sandy loam or loam soil under field conditions was studied. Soil was amended with manure inoculated with a Salmonella or E. coli O157:H7 cocktail, then transferred to 0.22 mu m pore size membrane walled vials. The vials were then placed on the surface or at 15 cm depth in the test plots. Pathogen numbers, soil moisture, rainfall, and temperature were measured throughout the three trials (20-47 weeks duration) representing spring or fall application. Survival curves were characterized by having an initial rapid decline in pathogen numbers followed by a slower inactivation phase with an occasional increase in culturable cells. The CT99.9 values (time to reach a 3 log CFU reduction) varied from 2 to 120 days, with the most rapid decrease being observed on the surface of sandy loam soil. The persistence of pathogens is primarily governed by variations in moisture and temperature, although season of application along with manure and soil type also contribute. To generate more accurate predictive pathogen models, there is a need for laboratory-based trials to mirror the dynamic variation in temperature and soil moisture encountered within the natural environment.