Soil Conditions That Can Alter Natural Suppression of Escherichia coli O157:H7 in Ohio Specialty Crop Soils
ABSTRACTFood-borne pathogen persistence in soil fundamentally affects the production of safe vegetables and small fruits. Interventions that reduce pathogen survival in soil would have positive impacts on food safety by minimizing preharvest contamination entering the food chain. Laboratory-controlled studies determined the effects of soil pH, moisture content, and soil organic matter (SOM) on the survivability of this pathogen through the creation of single-parameter gradients. Longitudinal field-based studies were conducted in Ohio to quantify the extent to which field soils suppressedEscherichia coliO157:H7 survival. In all experiments, heat-sensitive microorganisms were responsible for the suppression ofE. coliO157 in soil regardless of the chemical composition of the soil. In laboratory-based studies, soil pH and moisture content were primary drivers ofE. coliO157 survival, with increases in pH after 48 h (P= 0.02) and decreases in moisture content after 48 h (P= 0.007) significantly increasing the log reduction ofE. coliO157 numbers. In field-based experiments,E. coliO157 counts from both heated and unheated samples were sensitive to both season (P= 0.004 for heated samples andP= 0.001 for unheated samples) and region (P= 0.002 for heated samples andP= 0.001 for unheated samples). SOM was observed to be a more significant driver of pathogen suppression than the other two factors after 48 h at both planting and harvest (P= 0.002 at planting andP= 0.058 at harvest). This research reinforces the need for both laboratory-controlled experiments and longitudinal field-based experiments to unravel the complex relationships controlling the survival of introduced organisms in soil.