Effect of Proximity to a Cattle Feedlot on Escherichia coli O157:H7 Contamination of Leafy Greens and Evaluation of the Potential for Airborne Transmission

Abstract

cThe impact of proximity to a beef cattle feedlot on Escherichia coli O157:H7 contamination of leafy greens was examined. In each of 2 years, leafy greens were planted in nine plots located 60, 120, and 180 m from a cattle feedlot (3 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 bacteria 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 m, which was higher (P < 0.05) than the 1.8% of positive samples per plot at 180 m, 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 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. Current leafy green field distance guidelines of 120 m (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.T he consumption of fresh produce increasingly has been linked to human food-borne disease (1-4). In particular, leafy vegetables, such as spinach and lettuce, have become significant vehicles for the transmission of food-borne pathogens. Produce-associated outbreak surveillance data from the Centers for Disease Control and Prevention (CDC) for the period from 2000 to 2009 showed that among produce commodities, leafy greens were the most frequently linked to outbreaks (5). An analysis of published reports of U.S. fresh produce-associated outbreaks with an attribution risk ranking tool categorized the combination of leafy greens and Escherichia coli O157:H7 with the highest risk ranking score, followed by Salmonella enterica in tomatoes ranking second and S. enterica in leafy greens ranking third (6). For all U.S. foodborne disease outbreaks caused by Shiga toxin-producing E. coli (STEC) in the period of 1998 to 2008, leafy vegetables were the second most common implicated commodity, following beef (2). In addition, spinach, lettuce, and cilantro were commodities most associated with the recovery of STEC in produce market basket surveys conducted within the USDA Agricultural Marketing Service Microbiological Data Program from 2002 to 2012 (7). Leafy greens typically are consumed raw, so protecting these products from microbial contamination in the preharvest environment is critical to reducing the risk for food-borne illness. Potential sources of pathogens for preharvest produ...

Shiga Toxin (Verotoxin)-producing<i>Escherichia coli</i> and Foodborne Disease:A Review

“…In an outbreak of STEC O157:H7 infection associated with attendance at multiple rodeos that had used bulls from the same cattle supplier, isolates from all 14 patients showed indistinguishable PFGE pattern and isolates from nine patients had identical multiple-locus variable-number tandem repeat analysis (MLVA) patterns and five had minor differences, and an isolate of STEC O157 identified from a dirt sample collected from the bullpens of one of the attended rodeos was indistinguishable by PFGE and MLVA form the main outbreak strain 131) . STEC O157:H7 was recovered from 3.5% of leafy green samples of the plot at 60 m away from a cattle feedlot, whereas that was recovered from 1.8% of the samples at 180 m away from the same feedlot, suggesting airborne contamination with STEC O157:H7 from cattle production area 132) .…”

Survival of Salmonella enterica in Dried Turkey Manure and Persistence on Spinach Leaves

“…The handling of manure in agricultural environments (e.g., stacking, storing, application to fields, and transport from animal rearing operations to compost facilities) can lead to the unintentional airborne transfer of foodborne pathogens from the source of the manure to leafy green farms in proximal locations (4). As a result, the proximity of agricultural facilities with large amounts of manure may serve as a source of airborne contamination of leafy greens being cultivated in nearby fields (3,7). This possibility has been considered in the establishment of the leafy greens produce safety guidance, which recommends that leafy greens should not be grown within 400 ft of a source of manure or compost operation (7).…”

Contamination of Fresh Produce by Microbial Indicators on Farms and in Packing Facilities: Elucidation of Environmental Routes

“…Outbreak investigations on the farm and in packing facilities suggest that sources of produce contamination may include animal droppings, farmworkers' hands (subsequently simply referred to as "hands"), soil, agricultural water, tools, equipment, and other contact surfaces (6)(7)(8)(9)(10)(11)(12). Under laboratory conditions, such contamination events have been demonstrated (13)(14)(15)(16).…”