Feedlot E. coli study suggests new buffer areas are needed

Daily News
Dec 30, 2014
According to a new study from the U.S. Department of Agriculture’s U.S. Meat Animal Research Center, E. coli O157:H7 can spread more than a tenth of a mile downwind from a cattle feedlot onto nearby produce.

Whether or not this study sets the stage for new regulations remains to be seen, but first author Elaine Berry and her colleagues sampled leafy greens growing in nine plots (three each at 60, 120, and 180 meters downwind from the cattle feedlot at the research center) over a two-year period.

The rate of contamination with the pathogenic E. coli O157:H7 declined with distance. There was an average positive sample 3.5 percent of the time at 60 meters and 1.8 percent at 180 meters.

“In each of two years, leafy greens were planted to nine plots located 60, 120, and 180 meters from a cattle feedlot (three plots each distance). Leafy greens (270) and feedlot manure samples (100) were collected six different times from June to September in each year. 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 percent of leafy green samples per plot at 60 meters, which was higher (P < 0.05) than the 1.8 percent of positive samples per plot at 180 meters, indicating a decrease in contamination as distance from the feedlot was increased,” according to the authors.

The findings suggest that current buffer-zone guidelines of 120 meters (400 feet) from a feedlot may not be far enough.

Transmission of the pathogens is thought to be airborne. The researchers found E. coli in air samples at 180 meters from the feedlot, though the instruments were not sensitive enough to pick up E. coli O157:H7.

The highest levels of contamination on the produce were in August and September of 2012 after several weeks of very little rainfall and several days of high temperatures, conditions that appear to aid airborne transport of bacteria. In addition, increased cattle production activities during this time, created more 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 produce crops 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,” the authors wrote in their abstract.

“Results suggest that risk for airborne 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.”

Limitations of the research include that it was conducted only in one state—Nebraska, which is not a produce growing state. Nonetheless, Berry says that the location was a reasonable model for some of the U.S.’s major produce growing regions, such as California’s Central Coast, as winds there can blow almost as hard as in Nebraska, and both places can have dry summers, which are conducive to airborne transport of bacteria.

The research was published ahead of print in the journal Applied and Environmental Microbiology. — Traci Eatherton, WLJ Editor