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Persistence of Enteric Pathogens in Manure-Amended Soils in Northeast U.S. Produce-Growing Environments


<p>Identify the important factors, including post-harvest processing and storage conditions, potential routes of contamination, and consumer handling practices, that may affect the transfer and persistence of Salmonella spp., L. monocytogenes in whole and fresh-cut cantaloupes; determine how surface moisture, initial temperature, and storage conditions affect L. monocytogenes survival and growth; and assess contamination of field-grown melons when grown in soils where Salmonella spp. is present. Results will be used for the development of knowledge-based intervention strategies, risk assessment, FDA guidelines, and educational materials.</p>

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Cantaloupe melons, including 2 East and 3 West Coast cultivars, will be grown at BARC in soils contaminated with Salmonella spp. as well as in soils free of the pathogens. Cantaloupes harvested from soils free of Salmonella will be inoculated in the laboratory with a multi-strain cocktail of L. monocytogenes from the Jensen Farms outbreak. Persistence/growth of L. monocytogenes on inoculated melons will be assayed after temperature-controlled storage at 4 and 25 degrees C under constant humidity for up to 30 days. Cantaloupes will also be contaminated by exposure to specific surfaces (rollers, brushes, foam pads, plastic belts) which have been inoculated with L. monocytogenes. Transfer of the pathogens from these contaminated surfaces to the rind, stem-scar area, and to subsequent cut-melon pieces will be detected and quantified by conventional and advanced bacteriological recovery techniques. The effect of packinghouse operating conditions on the transfer of pathogens will also be assessed. The method of exposure which results in the greatest amount of transfer of pathogen to the cantaloupe surface will then be used as the inoculation method for the studies outlined below. Forced air cooling will remove field heat from melons using small-scale commercial coolers. Prior to cooling, melons will be surface inoculated and subjected to one of three cooling regimens. Internal and surface (rind) temperatures of selected melons placed at various positions within a pack will be recorded prior to and during the cooling operations. Inoculated melons will be subjected to the forced air cooling, and L. monocytogenes populations will be enumerated immediately before and after the cooling process. Uninoculated, field-grown cantaloupes will also be submerged in a suspension of L. monocytogenes and then cut to determine the extent of contamination into the flesh of melons. Different cutting methods and their effect on the transfer of L. monocytogenes from the rind to the flesh will be evaluated. Whole, contaminated melons will then be stored at 4, 10, and 25 degrees C for up to 20 days. On days 1, 3, 5, 10, and 20, melons will be cut and the flesh will be analyzed for the presence of L. monocytogenes. Cantaloupe seeds will also be sown in soils containing naturally present Salmonella spp. As plants grow, plant and soil samples will be taken and Salmonella spp. populations will be recovered. Cantaloupes at various stages of maturity will be analyzed for Salmonella populations to evaluate the correlation between the presence of Salmonella on melon rinds and in the soil. Salmonella spp. populations in soil, on plants, and on melons will be monitored throughout the harvest period of the melons. Melons will be analyzed to determine if Salmonella spp. prevalence differs by location on the melon (i.e., ground spot vs. top of melon) to provide an assessment of the distribution of the pathogen on the melon. Soil moisture and nutrients, including readily available N and carbon, pH, and organic matter content will be determined and used in correlation analyses with Salmonella spp. population data at various intervals within the harvest period.

Sharma, M.
University of Delaware
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