Purpose: The purpose of this study was to determine the fate of foodborne pathogens in soils covered with polyethylene plastic, biodegradable plastic, paper or straw mulches, or left uncovered (bare ground).
Methods: The surface 2 cm of soil in troughs (60 x 17 x 10 cm) were inoculated with a ~6 log CFU/ml cocktail of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica Newport. Soil troughs were covered with one of polyethylene plastic, biodegradable plastic, paper or straw mulch, or left uncovered as a bare ground control (4 replicates each), and held in a growth chamber maintained at day and night cycles of 17°C for 9 h and 30°C for 15 h, respectively. Soil samples (1 g) were collected periodically over a two week period during the first trial, and a three week period during the second trial. Pathogens in soil were enumerated by spread plating on selective agars. Significant differences among mulches and pathogens were determined by one-way analysis of variance (ANOVA) and Tukey’s test (significance level 0.05).
Results: Populations of pathogens in soils decreased significantly over time in both trials (P<0.01). Mulch had a significant effect on the survival of pathogens over time compared to bare ground (P<0.01), with the greatest pathogen survival under straw mulch. In both trials, L. monocytogenes persisted at significantly higher populations than E. coli O157:H7 and S. enterica Newport (P<0.01), and populations of E. coli O157:H7 declined the most rapidly (P<0.01).
Significance: Enteric pathogens persisted longer in soil covered with mulch compared to bare ground, with straw exhibiting the most significant effect.