Purpose: The fate of three foodborne pathogens, E. coli O157:H7, Listeria monocytogenes, and Salmonella enterica, in soil previously exposed to four different mulches was examined over a three-month period.
Methods: Soil was collected from lettuce plots covered with polyethylene plastic, biodegradable plastic, paper, or straw mulch, or bare ground (n = 4/mulch). Soil was transferred to potting trays containing 72 separate pots, and pathogen cocktails were applied separately. Trays were placed inside a growth chamber maintained at 21°C and 60% relative humidity. Pathogen populations were enumerated by spread plating or MPN enrichment.
Results: Biological replications were not significantly different. At time zero, no significant differences (P > 0.05) between populations (2.92 ± 0.5 log CFU/pot E. coli O157:H7, 6.42 ± 0.09 log CFU/pot L. monocytogenes, and 6.63 ± 0.2 log CFU/pot Salmonella) existed among mulch treatments or bare ground. Populations, declining over time in each mulch treatment, were either not significantly different or significantly different at only one time point; on days 3 and 28 biodegradable plastic had significantly higher E. coli O157:H7 and Salmonella populations, respectively. By three months, populations had decreased to -0.68 ± 0.16 log MPN/pot, -0.19 ± 0.09 log MPN/pot, and 0.18 ± 0.13 log MPN/pot for E. coli O157:H7, L. monocytogenes, and Salmonella, respectively. Salmonella populations declined significantly less than those of the other pathogens.
Significance: E. coli O157:H7, L. monocytogenes, and Salmonella may persist for durations exceeding three months in mulched soil and bare ground. Choice of mulch treatment does not have a significant effect on pathogen fate within soil.