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Quantifying Microbial Risks during Growth of Produce


The long term goal of this project is the development of quantitative risk assessments that will be used to identify production practices that may lead to increased risk of produce contamination and exposure to the consumer. An emphasis will be placed on quantifying risks, which if eliminated will lead to a reduction in the presence of foodborne pathogenic microorganisms (Salmonella spp.) on tomatoes.
While commodity specific food safety guidelines have been published for production of leafy greens and tomatoes with respect to potential risk factors during growth in the field, many guidelines are not scientifically based, or have been based on lab studies that have used unrealistic (high) levels of contamination. These studies have also only addressed contamination on edible portions of the plant pre-process (that is, before the vegetables have been washed and other wise processed and packaged). A unique aspect of our work is the fact that the produce will be harvested and processed prior to testing. This will allow for an estimation of the actual amount of contamination that is on the produce at a time relatively close to consumption, which should improve risk assessment models. <P>The description of the activities proposed is summarized by the following aims: <OL> <LI> To develop a better estimation of the true level of Salmonella contamination in imported produce. <LI> To investigate the potential for Salmonella contamination of tomatoes following application of contaminated pesticides using common industry methods. <LI> To investigate the potential of Salmonella contaminated soil to contaminate the entire tomato plant. <LI> To evaluate various temperature differentials (between process water and pulp) and contact time intervals, and effects on Salmonella internalization. <LI> To use the data obtained from this project as well as published literature and unpublished data to develop tomato specific quantitative microbial risk assessment models. <LI> To disseminate the research findings to stakeholders and academic and extension faculty.

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NON-TECHNICAL SUMMARY: Ongoing food safety outbreaks have necessitated the need to develop effective solutions to reduce the burden of foodborne disease related to the consumption of fresh produce. Currently, several research groups are conducting studies related to risk assessment of various parameters as they relate to the growth, harvest, processing, and transportation of fresh produce. The long term goal of this project is the development of commodity specific quantitative risk assessments that will be used to identify production practices that may lead to increased risk of produce contamination and exposure to the consumer. An emphasis will be placed on quantifying risks at time points as close to produce consumption as possible. Risks associated with the growth of produce will be quantified through experiments that entail sampling produce during the growth, harvest and processing stages to determine the prevalence of foodborne pathogens, and conducting artificial inoculation studies to understand the ecology of the pathogens during produce growth. The studies proposed here will be the first comprehensive attempt to integrate risk assessment data from multiple sources to produce programs that can evaluate microbial risks associated with future produce growing events. The results of the project will be communicated to interested stakeholders through symposia, targeted visits to vegetable growers and producers, and through electronic media. The risk assessment programs that will be created represent new tools with which the microbial safety of fresh produce can be enhanced.

APPROACH: For aim 1, samples of fresh produce and environmental samples will be obtained from farms in close proximity to the Texas/Mexican border and the samples will be tested for the presence of Salmonella by standard microbiological methods. Suspected Salmonella isolates will be confirmed by PCR. For aim 2, laboratory based studies will be conducted to examine the fate of Salmonella spp. in different foliar (pesticide) sprays. Several sprays commonly used in the industry will be prepared at several concentrations using water of differing quality, followed by inoculation with low (10E4 CFU/ml) concentrations of tomato outbreak strains including Salmonella enterica serovars Newport, Saint Paul, Montevideo, and Michigan. The pesticides will be stored at several temperatures including refrigerated temperature (4C) and temperatures that occur in the course of a normal growing season (15 - 35C). Microbial counts will be obtained, and these data will be used to establish survival and growth curves for the Salmonella strains in the different pesticides. In addition, these experiments will allow for an estimation of any serovar to serovar differences. in addition, avirulent Salmonella will be inoculated into the pesticides using parameters that lead to the most bacterial survival and growth, and the pesticide application method (drip vs spray) will be evaluated in order to quantify differences in transfer coefficients associated with transferring Salmonella to tomatoes through different methods of pesticide application. Additional parameters that will be assessed include the extent to which the presence or amount of organic material and dirt in pesticide sprays affect transfer of Salmonella to the tomatoes. Pesticides will be applied once per plant, either by spraying (using handheld sprayers) or by drip irrigation. Following the appropriate pre-harvest interval for each pesticide, tomatoes will be harvested, sorted, processed and tested for the presence of Salmonella as described above. For aim 3,contamination of soil will be investigated as a primary method to introduce Salmonella spp. to tomatoes. Soil will be contaminated with avirulent isolates of Salmonella and rain splatter will be investigated as a route of contamination with the use of an artificial rain simulator. the simulator will be used to simulate various levels (low, medium, high) of precipitation. For aim 4, various contact time and temperature differentials will be evaluated during processing in order to determine the extent to which Salmonella can be internalized into the pulp. For aim 5, data from all of the previous aims will be combined with published and unpublished data to develop microbial risk assessment models to determine the most important contamination routes associated with growth of contaminated tomatoes. Finally in aim 6, all data obtained from this project will be presented to stakeholders in the form of symposia. Outputs of the project will be evaluated by carefully designed surveys that will be developed to estimate behavioral change that was modified due to the research data that was presented.

Sofos, John; Goodridge, Lawrence
Colorado State University
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