2011 Annual Report
1a.Objectives (from AD-416)
The objectives are to: (1) Determine if E. coli O157:H7 can be transferred by dust or wind from cattle production environments to leafy green produce crops, (2) Determine the impacts of environmental conditions and proximity on the transmission of E. coli O157:H7 by dust or wind from cattle production environments to leafy green produce crops, and (3) Determine the impacts of environmental conditions and proximity on the density of flies and E. coli O157:H7-positive flies in a leafy green produce crop.
1b.Approach (from AD-416)
As a model for leafy green produce, spinach will be planted to nine plots in a 4.5-hectare field just north of the USMARC feedlot near Clay Center, Nebraska. Planting the target crop north of the feedlot will take advantage of prevailing south winds that are typical during the late spring and summer for this region. In each of two years, new spinach will be planted in each plot every two to three weeks from mid-May through late August to ensure there is leaf growth above ground continually from June to mid-September. The nine plots will be located at distances of 60, 120, and 180 m from the nearest row of feedlot pens (3 replicate plots at each of 3 distances). Rainfall volumes and intensity, air temperature, wind direction and speed, and relative humidity will be monitored and recorded at 15-min intervals by a weather station at the site. Thus, should E. coli O157:H7 be found to be transmitted to the spinach by airborne transport, effects of distance and other environmental factors on this process can be determined. At two-week intervals beginning in early June and continuing through mid-September, 30 spinach plants will be collected from each plot and feedlot surface soil samples will be collected from the feedlot pens. The presence of E. coli O157:H7 on the leafy portions of each plant sample and from each manure sample will be determined. In addition, the levels of generic E. coli on the spinach plants will be determined. During the periods of each year that E. coli O157:H7 prevalence in feedlot source samples is highest (typically August through mid-September), air and flies at each spinach plot and at the feedlot pens will be sampled and analyzed for E. coli O157:H7 and generic E. coli. Confirmed E. coli O157:H7 isolates will be subjected to PFGE analysis, in order to confirm linkage of any spinach isolates to cattle, air, or fly isolates.
A clear role for airborne transport in the dissemination of E. coli O157:H7 from cattle production environments to produce crops has not been demonstrated. In FY2011, we initiated studies to determine if E. coli O157:H7 can be transported by windborne aerosols from a cattle feedlot to a spinach crop, and if it is, to determine the impacts of environmental conditions and proximity on this airborne transport. In addition, we are examining cattle pest flies as potential sources of spinach contamination. Spinach plots were planted at locations 60, 120, and 180 meters from the nearest row of feedlot pens at a 6,000-head capacity feedlot. Spinach, air, fly, and feedlot manure samples were collected and analyzed for the presence of E. coli O157:H7. This information is critical to the produce industry for assessment of the risks associated with growing produce crops in close proximity to cattle feeding operations, and for defining appropriate distances for buffer zones that will reduce the risk of produce contamination.