Escherichia coli O157:H7 in bioaerosols from cattle production areas: evaluation of proximity and airborne transport on leafy green crop contamination.

Escherichia coli O157:H7 in bioaerosols from cattle production areas: evaluation of proximity and airborne transport on leafy green crop contamination.

Jan. 1, 2011 - Dec. 31, 2012

2011-136

$296,360.00

Elaine D. Berry, Ph.D.
USDA - ARS

James E. Wells, Ph.D.

Final Report

Publication

Publication

A clear role for dust or wind in the transport of Escherichia coli O157:H7 from cattle to produce crops has not been determined.  The research objectives are to: (1) Determine if E. coli O157: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 O157: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 O157: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 O157: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.

Technical Abstract

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.  The objectives of this work are to:  (1) Determine if E. coli O157:H7 can be transported by windborne bioaerosols from cattle production to leafy green crops, and (2) Determine the impacts of environmental conditions and proximity on the airborne transmission of E. coli O157:H7 by dust or wind from cattle production to leafy green crops.  In each of two years, spinach will be planted to nine plots in a 4.5-hectare field just north of the 6,000-head USMARC cattle 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.  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 (source 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, to provide supplemental information about the transport of this species by dust and/or wind and to provide quantitative data for risk assessment and modeling of the transport process.  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.  This work is anticipated to determine if indeed E. coli O157:H7 can be transported in windborne bioaerosols, and provide data regarding how this transport is influenced by environmental factors and distance.  This information is critical to the produce industry for assessing the risks associated with growing produce crops in close proximity to cattle production facilities, and for setting guidelines regarding buffer zone distances that are adequate to reduce contamination risk.