Foodborne pathogens have been estimated to cause 6 million illnesses and approximately 9,000 deaths each year (Mead et al., 1999). Escherichia coli O157:H7 was first associated with human disease during two investigations of hemorrhagic colitis in 1982 (Wells et al., 1983). Since then, E. coli O157:H7 has been the cause of numerous foodborne disease outbreaks in the United States and continued public attention has contributed to its emergence as a pathogen of significant public health concern. Several E. coli O157:H7 outbreaks have been linked to beef products, particularly the consumption of raw or undercooked contaminated ground beef. Knowledge contributing to the control of this pathogen continues to be a priority for the beef industry. The industry has been successful at identifying post-harvest methods to reduce the prevalence of this pathogen on carcasses. Various treatments have been designed to decontaminate carcasses, including the use of sanitizing agents such as hot water sprays, organic acid sprays, or combinations of these treatments (Castillo et al., 1998). Also, steam vacuuming has been shown to be effective in reducing the numbers of pathogens on carcasses (Kochevar et al., 1997).
Additionally, several packers are implementing innovative hide intervention technologies such as chemical dehairing, cetylpyridinium chloride (CPC), on-line hide wash cabinets, and ozonated and electrolyzed oxidizing (EO) waters. Nou et al. (2003) demonstrated that chemical dehairing effectively reduced the incidence of hide-to-carcass contamination with E. coli O157:H7. Bosilevac et al. (2004) tested the efficacy of a combined water wash and CPC treatment under conditions simulating a hide wash cabinet and concluded that the prevalence of E. coli O157:H7 was greatly reduced, resulting in near elimination of the pathogen prior to evisceration. On-line hide wash cabinets have been shown to reduce the prevalence of E. coli O157:H7 on hides, as well as pre-evisceration carcasses (Bosilevac et al., 2005a). Most recently, ozonated and electrolyzed oxidizing waters evaluated as a hide washing system were found to be effective methods of reducing the prevalence of E. coli O157:H7 on hides and carcasses (Bosilevac et al., 2005b).
Currently, the industry is making vast progress in the development of pre-harvest pathogen intervention strategies as well. Many of these technologies include vaccines, antibiotics, and feed additives administered to the animals at the feedlot. Ransom and Belk (2003) investigated several on-farm management practices as pre-harvest beef safety microbiological interventions, including a microbial feed additive, an antimicrobial feed additive, and a vaccine. They reported that all three interventions produced effective reductions of E. coli O157:H7 prevalence on hides and in feces.
The fact that some animals do not shed E. coli O157:H7 despite being exposed to stressful stimuli might be due to variation in stress response among individuals. Research on human subjects suggests that individuals neurologically respond to stressful situations with different regions of the prefrontal cortex (Rosenkranz et al., 2003). The neurological response seemed to be related to variation in the activation of the adrenal axis, which subsequently adversely affected the production of antibodies in response to an immune challenge.
This study was designed to examine the relationship between stress response and the fecal shedding of E. coli O157:H7. Much of the current research evaluating this relationship involves experimental inoculation of animals, along with the application of a specific stressor such as dietary or temperature changes. These types of parameters have been successful experimental techniques; however, these extremes do not sufficiently represent “real world” circumstances. To adequately represent “real world” conditions, steers and heifers, typical of those entering a commercial feeding operation, were utilized in this experiment, and these animals were handled according to common industry management practices.
The stated objectives for this work were:
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