Salmonella Prevalence Is Strongly Associated with Spatial Factors while Listeria monocytogenes Prevalence Is Strongly Associated with Temporal Factors on Virginia Produce Farms

Murphy, Claire M.; Weller, Daniel; Strawn, Laura K.

doi:10.1128/aem.01529-22

Cited by 3 publications

(1 citation statement)

References 63 publications

(128 reference statements)

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“…A 2020 review of agricultural water in the Southeastern United States noted that the geographical location of a water source played an important role in the prevalence and survival of foodborne pathogens ( 35 ). This conclusion is supported by other studies that compared microbial water quality between growing regions nationally ( 16 , 37 ) and locally ( 12 , 17 , 38 ), and between water types ( 32 , 39 – 41 ). Indeed, multiple studies have shown that this variability in water quality limits the efficacy of one-size-fits-all approaches to monitoring and mitigating microbial hazards in aquatic environments.…”

Section: Introductionsupporting

confidence: 77%

Methodological differences between studies confound one-size-fits-all approaches to managing surface waterways for food and water safety

Weller,

Murphy,

Love

et al. 2024

Appl Environ Microbiol

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Even though differences in methodology (e.g., sample volume and detection method) have been shown to affect observed microbial water quality, multiple sampling and laboratory protocols continue to be used for water quality monitoring. Research is needed to determine how these differences impact the comparability of findings to generate best management practices and the ability to perform meta-analyses. This study addresses this knowledge gap by compiling and analyzing a data set representing 2,429,990 unique data points on at least one microbial water quality target (e.g., Salmonella presence and Escherichia coli concentration). Variance partitioning analysis was used to quantify the variance in likelihood of detecting each pathogenic target that was uniquely and jointly attributable to non-methodological versus methodological factors. The strength of the association between microbial water quality and select methodological and non-methodological factors was quantified using conditional forest and regression analysis. Fecal indicator bacteria concentrations were more strongly associated with non-methodological factors than methodological factors based on conditional forest analysis. Variance partitioning analysis could not disentangle non-methodological and methodological signals for pathogenic Escherichia coli , Salmonella , and Listeria . This suggests our current perceptions of foodborne pathogen ecology in water systems are confounded by methodological differences between studies. For example, 31% of total variance in likelihood of Salmonella detection was explained by methodological and/or non-methodological factors , 18% was jointly attributable to both methodological and non-methodological factors. Only 13% of total variance was uniquely attributable to non-methodological factors for Salmonella , highlighting the need for standardization of methods for microbiological water quality testing for comparison across studies. IMPORTANCE The microbial ecology of water is already complex, without the added complications of methodological differences between studies. This study highlights the difficulty in comparing water quality data from projects that used different sampling or laboratory methods. These findings have direct implications for end users as there is no clear way to generalize findings in order to characterize broad-scale ecological phenomenon and develop science-based guidance. To best support development of risk assessments and guidance for monitoring and managing waters, data collection and methods need to be standardized across studies. A minimum set of data attributes that all studies should collect and report in a standardized way is needed. Given the diversity of methods used within applied and environmental microbiology, similar studies are needed for other microbiology subfields to ensure that guidance and policy are based on a robust interpretation of the literature.

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Section: Introductionsupporting

confidence: 77%

Methodological differences between studies confound one-size-fits-all approaches to managing surface waterways for food and water safety

Weller,

Murphy,

Love

et al. 2024

Appl Environ Microbiol

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Effects of Fumigation on the Reduction of Salmonella enterica in Soil

Gu,

Murphy,

Zheng

et al. 2023

Foodborne Pathogens and Disease

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Factors associated with foodborne pathogens and indicator organisms in agricultural soils

Cook,

Diekman,

Weller

et al. 2023

Front. Sustain. Food Syst.

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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 (Salmonella, Listeria monocytogenes) and concentration of indicator bacteria (total coliforms, generic Escherichia coli) 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 m2) per farm per visit for microbial and nutrient analysis (n = 240). Samples (25 g) were processed for Listeria spp. and Salmonella using a modified FDA BAM method; samples (5 g) were enumerated for generic E. coli and total coliforms (TC) using Petrifilm. Presumptive Listeria spp. and Salmonella 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. Salmonella prevalence was 4.2% (10/240), with 90% (9/10) recovered on Farm C. Listeria spp. and L. monocytogenes prevalence were 10% (24/240) and 2.5% (6/240), respectively. When samples were positive for generic E. coli (107/240), the average concentration was 1.53 ± 0.77 log10 CFU/g. Soil pH was positively associated with L. monocytogenes [Odds Ratio (OR) = 5.5] and generic E. coli (OR = 4.9) prevalence. There was no association between Salmonella prevalence and any evaluated factor; however, Salmonella 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.

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Salmonella Prevalence Is Strongly Associated with Spatial Factors while Listeria monocytogenes Prevalence Is Strongly Associated with Temporal Factors on Virginia Produce Farms

Cited by 3 publications

References 63 publications

Methodological differences between studies confound one-size-fits-all approaches to managing surface waterways for food and water safety

Methodological differences between studies confound one-size-fits-all approaches to managing surface waterways for food and water safety

Effects of Fumigation on the Reduction of Salmonella enterica in Soil

Factors associated with foodborne pathogens and indicator organisms in agricultural soils

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