Survival of Salmonella and Escherichia coli in Two Different Soil Types at Various Moisture Levels and Temperatures

With the increased consumption of fresh produce, a proportional increase in numbers of produce-related foodborne illness has been observed. An estimate of foodborne illness during 1998 to 2008 attributed similar to 46% of the incidences to produce. Any foodborne illness associated with produce can have devastating consequences to the industry. The most recent data from the Centers for Disease Control and Prevention implicate leafy vegetables, vine-stalk vegetables, root vegetables, and sprouts as the most common cause of produce-related foodborne outbreaks. Excess rainfall or flooding, mainly by altering levels of soil moisture and oxygen content, affects the microbial community in soil. The goal of this research was to determine the survivability of a three-serovar Escherichia coli and a five-serovar Salmonella enterica cocktail in microcosms prepared with Candler sand (CS) and Orangeburg sandy loam (OSL) soils. Microcosms were prepared with low, medium, and high volumetric water contents and were incubated at 20 and 30 degrees C. Serotyping was used to determine which E. coli or Salmonella serovar(s) from each cocktail persisted. Microcosm inoculation levels were similar to 7.0 log CFU/g. Sampling for CS and OSL microcosms incubated at 20 degrees C ended on day 364 and 357, respectively. The reduction of Salmonella and E. coli to below the limit of detection (extinction) in CS microcosms (incubated at 30 degrees C at all volumetric water content [VWC] levels) was reached on day 168 and 56, respectively. Extinction of Salmonella and E. coli in OSL microcosms (incubated at 30 degrees C at all VWCs) was reached on day 168 and 224, respectively. Of the Salmonella and E. coli serovars analyzed, Salmonella Javiana persisted the longest in both soil types, whereas E. coli O104:H4 and E. coli O145 persisted the longest in CS and OSL microcosms, respectively. Results from the current study suggest that soil type and temperature influenced pathogen persistence in CS and OSL soils more than moisture level and pathogen type.