Foodborne outbreaks have continued to be associated with produce contamination originating from on-farm sources, such as soil or agricultural water. Additionally, the heterogeneity of the pre-harvest environment complicates the development of universal strategies for managing produce safety risks. Understanding the ecology and epidemiology of foodborne pathogens and fecal indicator bacteria (FIB) by growing regions, sample types, scale of analysis, and detection method is essential for developing targeted mitigation strategies. This dissertation utilized quantitative research methods and statistical modeling to examine the impact of sampling method, spatial, temporal, meteorological, and physicochemical factors on pathogen prevalence and FIB levels. Key findings highlight that the drivers of prevalence differ between pathogens and were influenced by sample type, scale, and region.. The variations in associations emphasize that risk varies by space and time. Therefore, results support regional and scale-dependent food safety standards and guidance documents for controlling hazards to minimize risk. Additionally, the method used for pathogen detection influences prevalence highlighting the need for standard methods since methodological differences confound comparisons across studies. Furthermore, since agricultural water quality is an important food safety priority, this dissertation aimed to determine the efficacy of chemical antimicrobial sanitizers against Salmonella in pre-harvest agricultural water. Results demonstrated that certain sanitizer treatments and conditions can significantly reduce Salmonella populations in preharvest agricultural water sources and thus may serve as a risk reduction option when used correctly. / Doctor of Philosophy / Fresh fruits and vegetables are continually implicated in foodborne outbreaks. Additionally, the source of the pathogen that causes illness in these outbreaks is often due to contact with contaminated soil or water on the farm. Since the environment is extremely diverse, the risk of foodborne pathogens is not uniform across a farm and between farms. Therefore, the development of a one-size-fits-all plan to reduce the risk of foodborne pathogens from contaminating produce on a farm is difficult. Understanding the incidence and distribution of foodborne pathogens and fecal bacteria and how these microorganisms interact with the environment is important to develop strategies to manage risk. Additionally, understanding how the prevalence of bacteria varies by state, medium (water vs soil), and farm is needed to develop targeted mitigation plans. This dissertation utilized laboratory and field-based experiments to understand how space, time, weather, and physical properties impact the occurrence of foodborne pathogens and fecal bacteria. The primary results show factors that impact prevalence are different between pathogens (Salmonella vs Listeria vs E. coli). Furthermore, the occurrence differed by sampling method (molecular vs culture), sample type (water vs soil), scale (within a farm vs between multiple farms), and region emphasizing that the risk from foodborne pathogens varies over space and time. Overall, this dissertation's results suggest that both regional and scale-specific guidelines are needed to reduce foodborne pathogen risks in the farm environment. Lastly, since the quality of the water used in growing fresh produce is an important food safety priority, the effectiveness of chemical antimicrobial sanitizers against Salmonella in agricultural water was evaluated. Results demonstrated that certain sanitizer treatments and conditions (sanitizer concentrations, water temperatures) can significantly reduce Salmonella populations in pre-harvest water sources and may serve as a risk reduction option when sanitizers are used correctly.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/114794 |
| Date | 25 April 2023 |
| Creators | Murphy, Claire Margaret |
| Contributors | Food Science and Technology, Strawn, Laura K., Boyer, Renee Raiden, Weller, Daniel Lowell, Ovissipour, Reza |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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