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United States Department of Agriculture

Agricultural Research Service

Research Project: Food Safety Risk for Leafy Greens and Tomatoes from Small Farm Environments Exposed to Manure Dust, Soil Amendments, Insects and Creek Water

Location: Environmental Microbial and Food Safety Laboratory

2012 Annual Report


1a.Objectives (from AD-416):
Determine transference prevalence, survival, and quantities of E. coli, Salmonella, and fecal indicator microbes to leafy vegetables and tomatoes relative to proximity to composting and dairy operations, and to irrigation and agricultural sprays with treated and untreated surface waters tomatoes relative to proximity to composting and dairy operations, and to irrigation and agricultural sprays with treated and untreated surface waters.


1b.Approach (from AD-416):
Prevalence and concentrations of viable E. coli, Salmonella, and fecal indicator microbes will be measured prior to application of a common source of thermophilic and vermicomposted and non-composted aged dairy manure to small field and high tunnel plots where leafy greens and tomatoes are grown. Organic spring mix lettuce plants will serve as sentinels during land application and thereafter, several cultivars of tomato will be included in the replicated field and high tunnel plots. Plants will be arrayed on transects 50, 100, and 400 ft from animal and composting operations at BARC. Prevalence/ concentrations of microbes will be measured on plants at each distance from the suspected source and seasonally as well as in the suspected source materials (manure/compost). Particulate depositions onto lettuce and tomatoes will be measured and manure/compost prevalence in samples assessed by non-destructive fluorescence imaging techniques. Survival of microbes on produce will be assessed at seven days prior to harvest. The role of insects in transference of microbes from suspected nearby sources will be evaluated by imposing insect screening to exclude flying insects from plants in comparison with unscreened plants. Insects and dust at suspected sources and on unscreened fresh produce in nearby mini-plots will be captured and assayed for fecal indicators and pathogens and matched by genotype to those from suspected sources. Pathogen survival on leaves and in manure/compost will be evaluated relative to meteorological conditions during exposure periods and the physico-chemical and biological properties of the crop inputs. Creek water will be used directly and also sand filtered and treated treated with UV or chlorine prior to use in drip irrigation and crop protectant sprays. Non-pathogenic E. coli and Salmonella will be spiked into the creek water if none are naturally present. Impacts on survival of these microbes will be measured on spring mix lettuce and tomatoes.


3.Progress Report:

Improving food safety and reducing foodborne illnesses associated with fresh produce is a high priority national food safety goal. Current, industrial-scale production,harvesting, and processing practices for leafy greens and tomatoes stipulate certain metrics/procedures that require scientific evaluation. Some of these metric present potential major impediments for small-scale producers serving local communities. Field studies on airborne dispersal of microbial dispersal of fecal indicator microorganisms were planned and conducted at the University of Maryland Eastern Shore (UMES). The purpose of the studies was to assess the distance and concentration of E. coli, Staphylococcus, and Salmonella in airborne dust and fine particulates when broiler litter was moved from the poultry house to a manure spreader and subsequently when the manure spreader applied the litter to soil. Two types of microbial air samplers, mini-impingers and Andersen 6-stage samplers were used to capture airborne particulates upwind and downwind of the manure handling and application operations. Meteorological measurements of ambient conditions at the time of sampling were acquired. Microbial content of the broiler litter was assessed prior to the physical handling operations. Deposition onto tomato foliage was assessed. Results from these studies show that E. coli and Salmonella were rarely detected in the broiler litter that was used, but Staphylococcus was abundant. No E. coli or Salmonella were detected in any microbial air samples or from tomato leaf samples collected during litter loading into the spreader or during spreading operations, even as close as 25 feet downwind of the mechanical equipment. However, Staphylococcus was detected in abundance at 25 and 50 ft downwind in air and on leaf samples from tomato plants exposed to the dust. At 400 feet downwind of litter spreading, Staphylococcus was detected in some but not all air samples collected even under highly variable wind conditions. Further studies to repeat the initial tests are planned to confirm these results.


Last Modified: 9/10/2014
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