E. coli from feedlots spreads much further than
food safety investigators have expected.
Trials by a microbiology team revealed that
breezes can carry the bacteria at least 180 meters from feedlots.
That means produce growers need to keep their
crops further from feedlots.
The trials were run at distances of 60, 120 and
180 meters, and although fewer travelled the longer distances, some made it to
all three collection sites.
The highly risky strain, E. coli 0157:H7, was
among the strains that went as far as 180 meters.
That strain has sickened thousands and killed
scores of consumers across North America, including the sensational case of
poisoned water in the municipal distribution system at Walkerton, Ont. in 2000.
About 2,300 people were sickened and seven died in that case; the water was
probably polluted by cattle manure running into the river or wells after a
heavy spring rainstorm.
The new study has been published in Applied and
Environmental Microbiology.
Lead author of the study is Elaine Berry, a
researcher at the U.S. Department of Agriculture’s Meat Animal Research Center
at Clay Center, Nebraska.
In each of two years, leafy greens were planted
to nine plots located 60, 120, and 180 meters from a cattle feedlot (three
plots at 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, the team reports.
E. coli O157:H7 was recovered from 3.5 percent
of leafy green samples per plot at 60 meters, which was higher 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.
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.
Until this research, most assumed the feedlot
risk was from manure applied to fields or runoff into water used to irrigate
crops.
