Temporal stability of Salmonella enterica and Listeria monocytogenes in surface waters used for irrigation in the Mid-Atlantic United States

Authors: KIM, SEONGYUN - University Of Maryland; Pachepsky, Yakov; MICALLEF, SHIRLEY - University Of Maryland; ROSENBERG-GOLDSTEIN, RACHEL - University Of Maryland; HASHEM, FAWSI - University Of Maryland Eastern Shore (UMES); PARVEEN, SALINA - University Of Maryland Eastern Shore (UMES); KNIEL, KALI - University Of Delaware; SAPKOTA, AMY - University Of Maryland; Sharma, Manan

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2023
Publication Date: 2/6/2023
Citation: Kim, S., Pachepsky, Y.A., Micallef, S., Rosenberg-Goldstein, R., Hashem, F., Parveen, S., Kniel, K., Sapkota, A., Sharma, M. 2023. Temporal stability of Salmonella enterica and Listeria monocytogenes in surface waters used for irrigation in the Mid-Atlantic United States. Journal of Food Protection. 86(4). Article 100058. https://doi.org/10.1016/j.jfp.2023.100058.
DOI: https://doi.org/10.1016/j.jfp.2023.100058

Interpretive Summary: Pathogens in irrigation water sources create public health problems. Because of their usually low concentrations, monitoring pathogens is technically difficult and costly. Methods are needed for designing efficient monitoring strategies. We hypothesized that there might exist persistent spatial patterns in pathogen concentration distributions across different sampling sites so that concentrations at some sites are mostly higher than average across all sites, at other sites, concentrations are consistently lower than average, and finally, at some sites, they are not statistically significantly different from the average. The latter sites can represent the average concentration change in time. We tested this hypothesis with data from two years of monitoring of salmonella enterica and Listeria monocytogenes at six sites across the study area in the U. S. Mid-Atlantic. The stable spatial patterns in concentration distributions indeed existed. Concentrations at pond sites were consistently lower than average, and the concentrations at two of four stream sites were consistently higher than average. The other two stream sites represented the average concentration changes in time. The systematic deviations from the average were related to the between-site differences in rainfall for Salmonella and differences in temperature for Listeria, as well as to differences in water quality. These results will be useful for the water monitoring agencies and companies tasked to set the pathogen monitoring in irrigation water sources.

Technical Abstract: Enteric bacterial pathogen levels can influence the suitability of water sources for produce irrigation. We hypothesize that stable spatial patterns of Salmonella enterica and Listeria monocytogenes levels may exist across surface water sources in the Mid-Atlantic U.S. Water samples were collected at four streams and two pond sites in the mid-Atlantic U.S over two years, biweekly during the fruit and vegetable growing seasons and once a month during non-growing seasons. Two stream sites and one pond site had significantly different average concentrations in growing and non-growing seasons. The stable spatial patterns were found for relative differences between the site concentrations and average concentration across the study area. Mean relative differences were significantly different from zero at four sites for S.enterica and three sites for L. monocytogenes. The rest of the sites represented the average concentrations across the study area, i.e. all sampling sites. There was a similarity between the mean relative difference distribution between sites over growing period, non-growing period, and the entire observation period seven-day cumulative rainfall. Mean relative differences were determined for temperature, oxidation-reduction potential, specific electrical conductance, pH, dissolved oxygen, turbidity, and cumulative rainfall. The moderate-to-strong (> 0.657) Spearman correlation was found between spatial patterns of S. enterica and 7-day rainfall, and between relative difference patterns of Listeria monocytogenes and temperature (rs=0.885 and dissolved oxygen (rs =-0.885). We have also observed the persistence in ranking sampling sites be the concentrations of the two pathogens. Finding spatially stable spatial patterns in pathogen concentrations elucidates the spatiotemporal dynamics of these organisms across the study area and can facilitate the design of the microbial water quality monitoring.