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A clear role for dust or wind in the transport of Escherichia coli 0157:H7 from cattle to produce crops has not been determined. The research objectives are to: (1) Determine if E. coli 0157:H7 is transported by dust or wind from cattle production to leafy green crops, and (2) Determine the impacts of environmental conditions and proximity on any dust/wind transmission of E. coli 0157:H7. In each of two years, spinach will be planted in plots at distances from 60 to 180 meters from a cattle feedlot. Spinach plants will be collected every two weeks and examined for E. coli 0157:H7 and nonpathogenic E. coli. Weather data, including rainfall volumes and intensity, air temperature, wind direction and speed, and relative humidity will be recorded at 15-min intervals by an on-site weather station. Thus, if E. coli 0157:H7 is found to be transmitted to spinach by dust or wind, the effects of distance and other environmental factors on the transport process can be determined. This information is critical to the produce industry for understanding the risks associated with growing crops in close proximity to cattle production, and for determining safe distances between cattle feedlots and crop production.
Approach:
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.