Factors Associated with Foodborne Pathogens and Fecal Indicator Organisms in Virginia Agricultural Soils

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Date
2023-06-05
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Virginia Tech
Abstract

Prior research reveals foodborne pathogens, as well as enteric bacteria, can thrive in agricultural soils. Understanding how macro- and micronutrients, as well as meteorological factors and observational factors, impact pathogen prevalence may promote a better understanding of how pathogens persist in agricultural soils. This study aimed to (i), characterize associations between soil properties (e.g., macro- and micro-nutrient levels) and microbial targets (e.g., S. enterica and L. monocytogenes prevalence, fecal indicator bacteria concentration). Three produce farms in Virginia were selected from different regions (i.e., Blue Ridge Highlands, Piedmont, Coastal Plains). Farms were sampled four times to capture seasonal differences. Five soil samples were collected from 20 plots (25m2) and pooled in equal quantities to form one sample per plot. A total of 240 samples were collected. Listeria and S. enterica samples (25g) were processed using a modified FDA BAM method, while generic Escherichia coli (gEC) and total coliform (TC) samples (5g) were enumerated using Petrifilm. Presumptive Listeria and S. enterica positive samples were confirmed by PCR using a single gene. Bayesian mixed models were used to evaluate associations with each foodborne pathogen and indicator organism with factors of interest. S. enterica prevalence was 4.2% (10/240) in soil samples. Of the ten S. enterica positive samples, nine samples (90%) were from one farm in eastern VA. Listeria spp. prevalence was 10% (24/240) with L.monocytogenes prevalence being 2.5% (6/240). The average gEC and TC concentrations in soil samples were 1.53 (range 0.95-4.01) and 4.21 (range 1.23-7.12) log CFU/g, respectively. Bayesian mixed models revealed that pH impacted prevalence of L. monocytogenes and gEC (MAP=5.48, 95% CI=0.75,345.39, PD=0.98, ROPE=0.01), and (MAP=4.87, 95% CI=2.31,12.22, PD=1.00, ROPE=0.00). There was no evidence of an association between S. enterica prevalence and factors of interest. S. enterica was 11.55 times more likely to be detected on Farm C (where prevalence was highest) compared to other farms (95 % CI= 1.36, 1155.27, PD=0.98, ROPE=0.00). Findings show that while soil nutrient trends differ across all farms, it is difficult to determine the strength of these trends due to strong regional distinctions.

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Keywords
Listeria, Salmonella, Produce, Farm, Soil, Virginia
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