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<OL> <LI> Determine the prevalence, diversity, and quantity of bacteria associated with
organic as compared to conventional fresh produce in Maryland and Virginia.
<LI> Determine colonization and survival rates of bacterial pathogens associated with
selected organic and conventional fresh produce.
<LI> 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.
<LI> Determine the persistence and survival of Escherichia coli O157:H7 on fresh and
fresh-cut leafy green produce.
<LI> Compare the extent of enteric pathogen transmission by a chewing insect, Colorado
Potato Beetle, in organically- and conventionally-grown produce.
Approach: 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.