Applied and Environmental MicrobiologyPeer Reviewed Journal11/22/20142/1/2015Berry, E.D., Wells, J., Bono, J.L., Woodbury, B.L., Kalchayanand, N., Norman, K.N., Suslow, T.V., Lopez-Velasco, G., Millner, P.D. 2015. Effect of proximity to a cattle feedlot on Escherichia coli O157:H7 contamination of leafy greens and evaluation of the potential for airborne transmission. Applied and Environmental Microbiology. 81(3):1101-1110.

Interpretive Summary: Cattle are a significant source of the foodborne pathogen Escherichia coli O157:H7. Recent E. coli O157:H7 outbreaks of human disease linked to the consumption of spinach and lettuce demonstrate the need for information regarding E. coli O157:H7 transport from cattle production facilities. In particular, there is a critical need to determine safe set-back distances between fresh produce crops and cattle production that will reduce the risk for produce contamination. In this study, we evaluated the effect of distance from a beef cattle feedlot on E. coli O157:H7 contamination of leafy greens. Spinach, turnip greens, and mustard greens were planted in plots located 60, 120, and 180 meters (200, 400, and 600 feet) from a cattle feedlot. E. coli O157:H7 was found in leafy greens planted at all plot distances. E. coli O157:H7 contamination of leafy greens decreased as distance from the feedlot was increased. Results suggest that risk for airborne transport of E. coli O157:H7 is increased when feedlot pen surfaces are very dry and dusty, and when combined with cattle movement that generates airborne dust. The study results further suggest that the current leafy green industry set-back distance guidelines of 400 feet may not be adequate to reduce the occurrence of E. coli O157:H7 in leafy greens planted near cattle feeding operations. More research will be needed to determine safe set-back distances between cattle feedlots and crop production that will reduce the risk of fresh produce contamination.

Technical Abstract: The impact of proximity to a beef cattle feedlot on E. coli O157:H7 contamination of leafy greens was examined. In each of two years, leafy greens were planted to nine plots located 60, 120, and 180 meters from a cattle feedlot (3 plots each distance). Leafy greens, feedlot manure, and bioaerosol samples were collected from June to September. Both E. coli O157:H7 and total E. coli were recovered from leafy greens at all plot distances. E. coli O157:H7 was recovered from 3.5% of leafy green samples per plot at 60 meters, which was higher (P < 0.05) than the 1.8% of positive samples per plot at 180 meters, indicating a decrease in contamination as distance from the feedlot was increased. Although E. coli O157:H7 was not recovered from air samples at any distance, total E. coli was recovered from air samples at the feedlot edge and all plot distances, indicating that airborne transport of the pathogen can occur. Results suggest that risk for bioaerosol transport of E. coli O157:H7 from cattle production is increased when cattle pen surfaces are very dry, and when this situation is combined with cattle management or cattle behaviors that generate airborne dust. Current leafy green field distance guidelines of 120 meters (400 feet) may not be adequate to limit the transmission of E. coli O157:H7 to leafy greens planted near concentrated animal feeding operations. Additional research is needed to determine safe set-back distances between cattle feedlots and crop production that will reduce fresh produce contamination.