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The long term goals of our research are to understand the ecology of Escherichia coli O157:H7 in beef cattle and their environments and identify and evaluate effective preharvest intervention strategies to control or reduce prevalence of E. coli O157:H7 in cattle at the farm level. The aims of our continuing research are to develop and validate improved methods for the detection of E. coli O157:H7 in cattle feces and environmental samples, identify factors affecting gut persistence and fecal shedding of E. coli O157:H7, and to evaluate management strategies and production practices which could potentially be manipulated to reduce fecal shedding of E. coli O157 in cattle. This is a multi-step effort; potential animal and management factors are initially identified in field-based studies, and then these factors are tested using bacterial challenge models in cattle.<P> In this proposal, we will address the following specific objectives: <OL> <LI> Compare the genetic relatedness of E. coli O157 isolates from feces of cattle that were shedding at low (low shedders) or high levels (super shedders) and carcasses at slaughter. <LI> Evaluation of the association between feeding distillers grains (DG) and fecal shedding of E. coli O157:H7 in cattle, and <LI> Determine potential transmission of E. coli O157:H7 by house flies in cattle located in adjacent farms.
NON-TECHNICAL SUMMARY: The food supply in the United States is one of the safest in the world; however, food-borne illnesses do occur and frequently are associated with foods derived from animal agriculture. Escherichia coli O157:H7 is an important food-borne pathogen. Food products (beef and produce) contaminated with cattle feces are a major source of E. coli O157 in outbreaks. Despite rigorous surveillance of meat processors by the USDA Food Safety and Inspection Service, the number of confirmed human illnesses caused by E. coli O157:H7 continues at unacceptable levels. This strengthens the need for effective pre-harvest intervention strategies so that cattle with lower prevalence or pathogen load are presented for slaughter. Control strategies aimed at reducing the prevalence and concentration of E. coli O157:H7 in cattle feces, thus reducing the overall number of bacteria entering both the food and environmental pathways, may be the most effective approach for reducing the overall risk of human infections. Our research has focused on understanding the factors affecting the prevalence, magnitude and duration of fecal shedding of E. coli O157 with the long term goal of developing and validating practical on-farm control programs.
<P> APPROACH: E. coli O157:H7 shed in the feces of cattle is a primary source of contamination of meat and produce. We propose to assess the relationship of E. coli O157:H7 recovered from feces to that of isolates from in cattle that were shedding high or low levels of E. coli O157:H7 as they were presented for slaughter. Determination of genetic relatedness of E. coli O157:H7 isolates can provide valuable information on the pre-harvest ecology of this pathogen. Fecal and carcass samples will be collected from truckloads of finished cattle at a Midwest commercial abattoir. Matched fecal (rectal content) and carcass samples from a maximum of 32 animals will be collected from each of 45 truckloads of cattle from feedlots that fed DG and 45 truckloads of cattle from feedlots that did not feed DG. We will use pulsed-field gel electrophoresis (PFGE) to evaluate the genetic relatedness of the isolates. Our Evaluation of the association between feeding distillers grains (DG) and fecal shedding of E. coli O157 in cattle will provide confirmation and estimation of the magnitude of an association between E. coli O157:H7 and feeding cattle DG. In order to identify the potential component(s) in DG responsible for the positive association with E. coli O157, we will use in vitro fermentation systems with ruminal or fecal microbial inoculum. This is a simple and inexpensive approach for evaluating factors responsible for stimulating or inhibiting growth of E. coli O157 and other bacterial species. The in vitro fermentation systems will be used to assess the following factors or components of distillers grains such as, types, forms, individual components, etc., on the growth E. coli O157:H7 or other bacterial (non-O157 E. coli, Salmonella, etc.) species. We also propose to assess the potential transmission of E. coli O157:H7 by house flies from feedlot to dairy cattle. This will be done by collecting fecal samples and house flies from a feedlot and an adjacent dairy farm in the summer months, isolating E. coli O157:H7, and use PFGE to assess genetic relatedness.