MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE
Project Number: 1265-32420-004-00
Start Date: Apr 10, 2006
End Date: Apr 01, 2011
1. Determine the prevalence, diversity, and quantity of bacteria associated with organic as compared to conventional fresh produce in Maryland and Virginia.
2. Determine colonization and survival rates of bacterial pathogens associated with selected organic and conventional fresh produce.
3. Investigate the mechanism(s) of introduction and transference of E. coli O157:H7 to lettuce and leafy greens during growing, harvest, postharvest handlings and processing operations.
4. Determine the persistence and survival of Escherichia coli O157:H7 on fresh and fresh-cut leafy green produce.
5. Compare the extent of enteric pathogen transmission by a chewing insect, Colorado Potato Beetle, in organically- and conventionally-grown produce.
A farm-based investigation will be conducted to assess the prevalence, diversity, and quantity of epi- and endophytic saprophytes and gastroenteric bacteria associated with organic as compared to conventional fresh produce. Bacterial analyses will include use of microbial cultural and molecular methods to characterize the enteric and saprophytic microflora on fresh market produce types most commonly reported in foodborne illness outbreaks: tomatoes, salad greens: lettuce, arugula, mesculin, spinach, beets; herbs: basil, cilantro, parsley; strawberries; cucurbits: cucumbers and melons. In addition, practices at each farm will be identified and characterized to associate analytical results with microbial quality of farm inputs and operations. Bacterial analysis will include total aerobic heterotrophic bacteria, enteric bacteria (coliforms), Aeromonas spp., Bacillus cereus, C. perfringens, E. coli, Enterococcus spp., L. monocytogenes, and Salmonella. Microbial community analysis of epi- and endophytic bacteria by DGGE will be used for tomato fruit and salad greens from organic and conventional farms. Growth chamber and field plot experiments will be conducted to establish the pathogen concentrations required to establish populations that survive on different plants (e.g., tomatoes, greena, basil, scallions, carrots, and strawberries). Survival of pathogens (Aeromonas, EHEC, L. monocytogenes, and Salmonella) on/in plants grown in organic and conventional soils with composted or aged manure (spike with pathogens) and irrigated with contaminated river water or sprayed with compost tea will be determined by enrichment and enumeration of rhizosphere, cortical root tissue, and/or on the edible portion of plants. Organic practices that can prevent pathogen growth in compost tea and internal plant tissues will be evaluated in growth chamber and field studies with tomato. Finally, the potential for a chewing insect, Colorado Potato Beetle, to transfer bacterial pathogens to the surface and interior tissue of tomato plants and initiate systemic colonization will be investigated for organic and conventional production methods.