An official website of the United States government.

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Control of Food-Borne Pathogens in Pre- and Post-Harvest Environments


<Ol> <LI> Develop or improve methods for control or elimination of pathogens in pre-and post harvest environments including meat, poultry, seafood, fruits and vegetables and nutmeats. <LI> Develop and validate mathematical modeling to gain understanding of pathogen behavior in macro and micro-environments. <LI> Investigate factors leading to the emergence, persistence and elimination of antimicrobial resistance in food processing and animal production environments. </ol> Projected Outputs, Outcomes & Impacts. <Ol><LI> Validated decontamination methods that can be used by the fruit, vegetable, seafood, meat and poultry industry to enhance the safety of their finished product. <LI> Outreach/extension education and training materials for regulatory personnel, producers, processors, consumers, extension agents. <LI> Overall enhanced food safety for consumers.

More information

NON-TECHNICAL SUMMARY: An increasing number of gastrointestinal disease outbreaks have been linked to the consumption of fresh fruits and vegetables. Two foodborne pathogens, Salmonella and Escherichia coli O157:H7, have been responsible for many outbreaks associated with fresh fruits and vegetables and nuts. Fresh fruits and vegetables are of concern because they are minimally processed and are susceptible to contamination. Our overall goal is to develop or improve methods for control or elimination of pathogens in pre-and post harvest environments including fruit, vegetables and nutmeats. Factors affecting survival preharvest and during postharvest handling will be studied. Results of these studies will be used for development of outreach training and publications. Information gained from this research will reveal the adequacy and appropriateness of practices currently used in the tree nut and lettuce industries in terms of controlling and eliminating Salmonella or E. coli O157:H7. This knowledge will form the scientific basis for the adequacy of or need to improve these practices. We will partner with the nut and lettuce industry to disseminate this new information and to evaluate its application and implementation; ultimately improving the safety of these products.


APPROACH: This proposal will, through laboratory studies, identify points during post-harvest handling of treenuts where Salmonella may be reduced, controlled or amplified. Emphasis will be placed on understanding the behavior of inoculated Salmonella during hulling, drying and long-term storage. Working with the industry, the overall goal of this research is to use the laboratory data to develop scientifically-based food safety risk-reduction strategies for the treenut industry. Nut kernels or in-shells or other pre-or post-harvest materials (hulls, shells, processing water, etc.) will be inoculated at 3 to 9 log CFU/g with a cocktail of Salmonella as appropriate to the study. Hulling, shelling and drying, storage at different temperatures, pasteurization methods may be evaluated as appropriate. Salmonella will be recovered from samples using previously described methods or modifications of these methods as appropriate. Samples will be analyzed for presence of Salmonella by plating using standard methods developed for almonds and, when appropriate, by enrichment. As necessary, modifications will be made to this procedure for other inoculated products. When appropriate, the FDA BAM method will be used for enrichment. Inoculated product will be held or exposed to different conditions that would be encountered in the pre or post-harvest nut environment. Field trials will be conducted in California to assess the fate of inoculated, attenuated non-pathogenic rifampicin-resistant E. coli on lettuce. Drip and sprinkler irrigation will be compared in May and July (early and late summer) plantings. Romaine lettuce will be inoculated after thinning (approximately 4 weeks after planting) by spraying prepared cell suspension on each plant. At each time point (from day 0 to 28) 10 to 20 samples will be randomly selected from each of 3 replicates. The test organism will be recovered from lettuce and soil using standard methods. Enumeration, filtration and enrichment methods will be used. By combining different methods the detection limit can be pushed to 10 CFU/lettuce head after which enrichment of lettuce heads will be performed. Precipitation data, soil and air temperatures, and storm report data collected from nearby weather stations accessed online from the California Irrigation Management Information System (CIMIS) and the National Climatic Data Center (NCDC) of the National Oceanic and Atmospheric Administration (NOAA). These will be supplemented by temperature data collected directly in the inoculated field. Field data will be used to validate growth chamber experiments for further study of factors impacting survival of E. coli on growing lettuce plants. The results of the combined work should help to inform growers of strategies that would mitigate the risk of the organism surviving after a contamination event.

Harris, Linda
University of California - Davis
Start date
End date
Project number
Accession number