A Novel Strategy to Test and Monitor Beef Feedlot Food-Safety Control Points

NON-TECHNICAL SUMMARY: Food safety could be enhanced if food-borne pathogens, such as Escherichia coli O157:H7 and Salmonella could be controlled during live cattle production. Being able to determine the E. coli O157:H7 status of feedlot cattle is important for feedlot production food safety research and HACCP monitoring. However, determining if individual live cattle are shedding E. coli O157:H7 or Salmonella is expensive and impractical. The goal of this project is to improve food safety by developing efficient, effective methods to determine the E. coli O157:H7 and Salmonella status of pens of feedlot cattle and to reduce the potential that these foodborne pathogens leave the feedlot. Pen testing will reduce time, cost, and labor and avoid detrimental animal welfare effects of handling finished cattle prior to shipping (shrink, dark cutters, and bruising). Additionally, most conceivable interventions to reduce human foodborne pathogens in feedlot cattle are directed towards pens. A pen-testing protocol has been identified that shows promise as a monitoring tool for feedlot production HACCP programs and as a research tool to identify and test potential HACCP control points. Objectives of this project are to complete validation of this pen- test for E. coli O157:H7 and Salmonella shedding; determine what a positive (or negative) pen test means in terms of length of time cattle may be shedding E. coli O157:H7 or Salmonella in commercial feedlots; identify potential control points using risk factor analyses; and disseminate results to researchers, industry partners and consumers.

<P>

APPROACH: A cross-sectional study will be used to measure agreement between pen- level tests and individual-level fecal shedding of cattle. Feces will be cultured for E. coliO157:H7 and Salmonella from all cattle in representative feedlot pens from commercial feedlots during late spring, summer and winter. Likelihood estimates will be used to determine prevalence cut-offs. This will provide validated sensitivity and specificity measures for pen testing methods. Concurrently, information will be collected and analyzed to identify pen characteristics associated with increased prevalence of cattle shedding E. coli O157:H7 or Salmonella. Prospective longitudinal weekly sampling will document whether the prevalence of E. coli O157:H7 or Salmonella changes with days on feed. The relationship between pen prevalence and duration of positive pen tests will be analyzed. This will identify the best locations, time intervals and period during the final weeks of the feeding cycle to conduct pen testing. If pen-test status changes over time for individual pens, pen and temporal factors associated with the initiation and duration of shedding will be examined. This information is needed to design, implement, and to evaluate the effectiveness of control measures. We will present results to our communities of interest through scientific journals, at scientific meetings, and to researchers, veterinarians, cattlemen, feedlot personnel, extension educators, food safety personnel and others regionally and nationally through workshops, presentations, demonstrations, newsletter, and other written guides as appropriate for the audience. <P>

PROGRESS: 2000/11 TO 2004/10<BR>
Although cattle are important reservoirs, no validated method exists to monitor E coli O157:H7 on farms. In 29 Midwestern US feedlot pens we compared culturing feces from the individual cattle to: 1) culturing rope devices that cattle rub or chew (ROPES); and 2) culturing a composite of fecal pats. Eighty-six percent (68%-96%) of pens were classified correctly using rope devices to detect pens with at least 16% of the cattle shedding STEC O157 [sensitivity = 82% (57%-96%); specificity = 92% (62%-100%)]. Ninety percent of pens (73%-98%) were classified correctly using composite-feces to detect pens with at least 37% of the cattle shedding STEC O157 [sensitivity = 86% (42%-100%); specificity = 91% (71%-99%)]. Ranking pens into 3 risk levels based on parallel interpretation of the pen-test results correlated (Spearman's r = 0.76, p<0.0001) with the pen's prevalence. This strategy could identify pens of cattle posing higher risk to food safety. Why E. coli O157:H7 varies by time and place in fed cattle is poorly understood so we conducted a two year two season longitudinal study to describe and explain the occurrence of E. coli O157:H7 and Salmonella by pen-level factors of time and place using ROPES to monitor the pens of cattle. From each pen, we cultured seven ropes placed within pens for cattle to rub and chew (ROPES), in order to classify the pens as high or low prevalence. Recovery of the pathogen from at least one rope classified the pen as ROPES-positive. Pens ROPES-positive for E. coli O157:H7 clustered temporally. Factors associated with ROPES-positive pen-weeks during both the summer and winter feeding periods were feedyard, prior 7-day mean air temperature, recovery of E. coli O157:H7 from the composite fecal sample, and recovery of E. coli O157:H7 from the water tank. Pens of summer-fed cattle were less likely to be ROPES-positive for E. coli O157:H7 if the ROPES were positive for Salmonella spp. The condition of the pen surface was associated with the likelihood for winter-fed pens of cattle to be ROPES-positive. We observed differences in occurrence of ROPES-Salmonella-positive pens by weeks within each season such that, at times, a high proportion of pens were of the same ROPES-status even though feedyards were separated by 50-200 km. Factors associated with ROPES-positive pen-weeks during both the summer and winter feeding periods were the condition of the pen surface and recovery of Salmonella spp. from the water tank. The probability for pens of summer-fed cattle to be ROPES-positive for Salmonella spp. increased as the number of cattle in the pen increased and decreased when the pen was ROPES-positive for E. coli O157:H7. Pens of winter-fed cattle differed by feedyard in their probability to be ROPES-positive for Salmonella spp. We were able to monitor these pens of cattle using ROPES at minimal cost and without disturbing individual cattle.
<BR> <BR>
IMPACT: 2000/11 TO 2004/10<BR>
Understanding when and where food safety pathogens occur in cattle feedlots enable us to speculate on ways to control those agents. We also need this information so that we can design clinical trials to test interventions.