AUTHOR=Cook Camryn , Diekman Clara M. , Weller Daniel L. , Murphy Claire M. , Hamilton Alexis M. , Ponder Monica , Boyer Renee R. , Rideout Steven L. , Maguire Rory O. , Danyluk Michelle D. , Strawn Laura K. 

TITLE=Factors associated with foodborne pathogens and indicator organisms in agricultural soils

JOURNAL=Frontiers in Sustainable Food Systems

VOLUME=7

YEAR=2023

URL=https://www.frontiersin.org/journals/sustainable-food-systems/articles/10.3389/fsufs.2023.1269117

DOI=10.3389/fsufs.2023.1269117

ISSN=2571-581X

ABSTRACT=<p>Soil can be a route for contamination of fresh fruits and vegetables. While growers routinely manage soil nutrient levels, little research exists on the synergistic or antagonistic effects of soil nutrients on foodborne pathogens. Data on foodborne pathogen prevalence in unamended soils is also relatively limited in literature. This study evaluated foodborne pathogen prevalence (<italic>Salmonella</italic>, <italic>Listeria monocytogenes</italic>) and concentration of indicator bacteria (total coliforms, generic <italic>Escherichia coli</italic>) in agricultural soils, and characterized associations between soil properties (e.g., macro- and micro-nutrient levels) and each microbial target. Three Virginia produce farms, representing different regions and soil types, were sampled four times over 1 year (October 2021–November 2022). For each individual farm visit, composite soil samples were collected from 20 sample sites (25 m<sup>2</sup>) per farm per visit for microbial and nutrient analysis (<italic>n</italic> = 240). Samples (25 g) were processed for <italic>Listeria</italic> spp. and <italic>Salmonella</italic> using a modified FDA BAM method; samples (5 g) were enumerated for generic <italic>E. coli</italic> and total coliforms (TC) using Petrifilm. Presumptive <italic>Listeria</italic> spp. and <italic>Salmonella</italic> isolates were confirmed by PCR using the sigB and invA genes, respectively. Soil nutrients from each sample were tested and evaluated for their association with each microbial target by Bayesian Mixed Models. <italic>Salmonella</italic> prevalence was 4.2% (10/240), with 90% (9/10) recovered on Farm C. <italic>Listeria</italic> spp. and <italic>L. monocytogenes</italic> prevalence were 10% (24/240) and 2.5% (6/240), respectively. When samples were positive for generic <italic>E. coli</italic> (107/240), the average concentration was 1.53 ± 0.77 log10 CFU/g. Soil pH was positively associated with <italic>L. monocytogenes</italic> [Odds Ratio (OR) = 5.5] and generic <italic>E. coli</italic> (OR = 4.9) prevalence. There was no association between <italic>Salmonella</italic> prevalence and any evaluated factor; however, <italic>Salmonella</italic> was 11.6 times more likely to be detected on Farm C, compared to other farms. Results show pathogen prevalence was relatively low in unamended soils, and that factors influencing prevalence and concentration varied by microbial target and farm.</p>