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Microbiological risk assessment using QMRA in preharvest agriculture water treatment systems for leafy greens


To date, agricultural water treatment research has heavily focused on the efficacy of available chemistries/devises at reducing microbiological indicators including generic Escherichia coli (E. coli) and Total Coliform bacteria in water. While key learnings have led to a strong understanding of the conditions needed to achieve reductions of pathogens/indicators in agricultural water itself, there remains a significant knowledge gap of the impact that treated agricultural water has on pathogens already established on plant surface(s) or in soil. Additionally, there is a lack in understanding of the risk to human health that agricultural water treatment variability or “breakthrough” has when associated with the consumption of fresh leafy greens. This proposal aims to directly address these knowledge gaps by using laboratory and field evaluation coupled with Quantitative Microbial Risk Assessment (QMRA). The specific objectives of this project are: (1) Determine the die-off or log-reduction of E. coli O157:H7 and generic E. coli surrogates pre-established on leaf surface and in soil following agricultural water treatment using commonly used water treatment sanitizers (PAA and Calcium Hypochlorite); (2) Conduct in-field evaluations with grower collaborators of water treatment variability or “breakthrough” using traditional grab sampling techniques for microbiological indicators (generic E. coli and Total Coliform bacteria) coupled with real-time in-line monitoring for physical/chemical parameters (PAA, free chlorine, pH, temperature, ORP, flow rate in gpm); and (3) Use real world collected data from Objectives 1 and 2 to conduct a QMRA for STECs in leafy greens (romaine and spinach). Success of the project will include a comprehensive understanding of the impact of residual agricultural water treatment chemistries on pathogen persistence in water, on plant tissue and in soil and how it relates to risk. It is anticipated that scientific data will be generated which growers can use to justify enhanced benefits of their antimicrobial water treatment beyond die-off of organisms found in agricultural water alone. The study will also evaluate treatment systems at a commercial scale production to document critical time periods and durations of treatment variability that may result in a loss of effectiveness due to decreased residual, and all taken together will result in improved estimates of risk to human health. Ultimately, the study aims to provide growers and regulators with an improved understanding of the impact of water treatment on risk reduction for consumers.

Channah Rock, Ph.D.; Charles Gerba, Ph.D.; Kerry Cooper, Ph.D.; Kerry Hamilton, Ph.D.
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