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Evaluation of risk factors and detection of selected foodborne pathogens associated with fresh produce




Coleman, Shannon M., author
Goodridge, Lawrence, advisor
Bunning, Marisa, committee member
Woerner, Dale, committee member
Newman, Steven, committee member

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The Economic Research Service (ERS) of the United States Department of Agriculture (USDA) has reported increases of greater than 40 pounds per capita in yearly fresh produce consumption over the last 30 years. Outbreaks associated with fresh produce have also increased with an estimated 46% of foodborne outbreaks attributed to the consumption of various types of fresh produce from 1998 to 2008. One of the foodborne pathogens of concern is Salmonella spp., the leading cause of foodborne illness hospitalizations and deaths in the United States (US). Salmonella species are ubiquitous microorganisms necessitating increased need for proper surveillance. Testing for major pathogens such as Salmonella spp. and Escherichia coli O157:H7 in produce is impractical due to large retail volume, variability of contamination, and low sensitivity of current platforms. Irrigation, wash waters, and other agricultural sources offer greater probability for pathogen detection when combined with appropriate sample preparation. One food commodity commonly linked to Salmonella spp. outbreaks is tomato. Greenhouse/hydroponic production currently accounts for a large share of tomato production and has had a significant impact on the U.S. fresh-tomato market. There is little known about the possibility of contamination and internalization of foodborne pathogens via greenhouse/hydroponic commercial production since these operations are usually considered relatively sanitary due to the closed environment. I evaluated the risk factors associated with fresh produce contamination such as contaminated irrigation water and agricultural sources using simple sample preparation, subtyping techniques, and rapid molecular testing. This research is comprised of three study topics: development of an irrigation water concentration method with subsequent detection of Salmonella spp. and E. coli O157:H7 using Vitek Immuno Diagnostic Assay (VIDAS) technology, comparison of molecular serotyping methods to conventional serotyping methods for Salmonella enterica subsp. enterica isolates from food and agricultural sources, and evaluation of contaminated irrigation water as a risk factor for contamination of hydroponically grown tomatoes. Novel molecular methods were used in the three studies, including VIDAS UP® technology, Automated RiboPrinter, Luminex® xMAP Salmonella serotyping assay, and pulsed-field gel electrophoresis to detect foodborne pathogens. Results showed that a novel concentration method was effective in concentration of Salmonella spp. and E. coli O157:H7 with subsequent detection via mini VIDAS® technology. Molecular serotype methods were unable to serotype isolates obtained from agricultural sources. However, molecular methods allowed us to identify serovars associated with food and clinical sources. Salmonella Typhimurium did not survive well in the nutrient solution of a conventional hydroponic system used in tomato production. We also discovered that continuous contamination with S. Typhimurium might lead to contamination of the root systems but not contamination of the leaves and fruit. This work illustrates the continuing need to evaluate production methods and pathogen detection techniques to improve the safety of fresh produce.


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Escherichia coli O157:H7
Salmonella spp.
fresh produce


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