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Mechanisms Associated with Contamination of Fresh and Fresh-Cut Fruits and Vegetables by Pathogenic Microorganims and Development of Control


The overall objective of this project is to determine mechanisms for food-borne pathogenic microorganisms to contaminate and colonize fresh and fresh cut fruits and vegetables and to develop pre and post harvest strategies for their control and/or elimination. Specific goals are listed for each principal investigator on this project.

<P>Objective #1: To determine routes by which food-borne pathogenic bacteria contaminate produce commodities under pre-harvest conditions, including environmental persistence and potential for pathogen to internalize into fruit during growth. <BR>Goal #1: To determine the survival and persistence of food-borne pathogen in soil conditions. <BR>Goal #2: To determine potential for food-borne pathogens to be transferred via irrigation water through root systems and tissues of fruit bearing plants resulting in contaminated fruit. <P>

Objective #2: To characterize the microbial communities present on cut and whole surface produce and determine interactions between human enteric pathogens and normal background flora. <BR>Goal #3. Determine composition of the normal background flora of spinach, lettuce and tomatoes <BR>Goal #4. Identification of members of native microbiota that inhibit growth and survival or compete with enteric pathogens <P>

Objective #3: To determine the effect of post harvest process interventions on survival and persistence of food-borne pathogens. <BR>Goal #5: To determine the effect of packaging and storing fresh and fresh cut fruits and vegetables under modified and controlled atmospheres on the survival and persistence of food-borne pathogens. <BR>Goal #6: To determine parameters for the application of high hydrostatic pressure processing to reduce or eliminate Salmonella enterica serovars from fresh and fresh cut tomatoes. <P>

Objective #4: Identify candidate genes important in the survival and attachment of human enteric pathogens on plants. Are known virulence genes implicated? <BR>Goal #7: To identify extracellular proteins which influence ability of food-borne bacterial pathogens to attach to and colonize plant surfaces. <BR>Goal#8: Determine global transcriptional response of various serotypes of Salmonella enterica in the presence of native microflora and under minimal processing conditions

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NON-TECHNICAL SUMMARY: Each year in the United States, 13.8 million illnesses are attributed to food-borne transmission. Two common bacterial food-borne pathogens, Salmonella enterica and Escherichia coli O157:H7 are responsible for an estimated 1.4 million and 79 thousand illnesses each year. In 2005 (the most recent available data) serotypes of S. enterica accounted for 45,322 illnesses, while E. coli O157:H7 resulted in 2,621 cases of food-borne illness that were reported within the United States. The state of Virginia, accounted for 1172 (approximately 2.6%) of these Salmonella enterica and 53 (approximately 2.1%) of E. coli O157:H7 infections. Agricultural crop losses due to food-borne disease typically top 100 million dollars per year, while medical associated costs are even higher. Annual economic losses due to Salmonella enterica and E. coli O157:H7 infections are estimated at 0.6 to 3.6 billion and 405 million, respectively, depending on the severity of the disease. Due to the high economic and health costs associated with these two bacterial diseases a better understanding of reservoirs and control strategies are necessary for the completion of the mission of the Virginia department of Agriculture to promote consumer protection and economic growth. Traditionally, foods of animal origins have been associated with food-borne illness. Recently, the number of outbreaks associated with contaminated fruit or vegetables increased 8-fold from 1973 to 1997. The most frequently identified etiologic agents associated with fresh produce are E. coli O157:H7 and serotypes of the bacterium Salmonella enterica. This organism has been implicated in outbreaks associated with salad, cilantro, seed sprouts, berries, melon, juice, mixed fruit, and tomatoes. From 1982 to 2002, 21% of all E. coli O157:H7 outbreaks were linked to produce. Lettuce is the most common vegetable associated with E. coli O157:H7 produce outbreaks (34%). These outbreaks have raised concerns about the pre-harvest contamination by human pathogens, particularly Salmonella enterica and E. coli 0157:H7. The largest impact factor in the increase of produce associated outbreaks has been the increased availability of fresh produce, in minimally processed, ready to eat forms. These products do not use traditional thermal processing techniques that would kill human pathogens due to undesirable effects on the product. An increased understanding of the interaction between the pathogen, host plant and associated microbiota is necessary to and to identify and control colonization of fresh produce by human pathogens. The results from this study will provide increased knowledge in the subject of pathogen / host interactions from the perspective of food-borne pathogens and their interactions with plants. Impacts may include recommendations to the fruit and vegetable industry in Virginia regarding planting and irrigation strategies to reduce potential for pathogen contamination in the pre- and post harvest environments. Alternative storage and processing methods will be evaluated which may lead to the industry adopting acceptable interventions to reduce microbial load and increase quality of produce products.
APPROACH: This project will primarily be conducted in field and laboratory settings using general scientific methods. Procedures will focus on both culture based methods for recovering microorganisms as well as molecular techniques. Where applicable, recovery of pathogens by direct plating will be analyzed using the mixed procedure of SAS version 8.1. The experimental design will be set up using a randomized complete block design, factorial treatment arrangement, repeated measures with sampling blocked upon replicate. Means will be separated using Tukey's HSD when significant differences occur. Research results will be disseminated through presentations at scientific meetings such as International Association for Food Protection, Institute of Food Technologists and American Society for Microbiology. Additionally, results will be published in refereed scientific journals. Research with industry and extension impact will be reported in extension publications, trade journals and workshops.

Boyer, Renee
Virginia Polytechnic Institute and State University
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