Beef producers have invested over $20 million since 1993 to improve beef safety via development and validation of interventions, as well as changes in sampling and testing procedures (National Cattlemen’s Beef Association, 2003b). The top ten beef packers have spent $400 million in the last decade to address E. coli O157:H7 contamination of beef by use of processing-level microbiological interventions (Kay, 2003). Points of Focus for the Producer Sector, to reduce the prevalence of E. coli O157:H7 associated with market-ready cattle, as identified at the E. coli Summit meeting (National Cattlemen’s Beef Association, 2003b) included: (a) Maintain present Good Management Practices (GMP) of clean feed, clean water, clean pens and clean cattle, (b) Evaluate adoption of interventions or GMP that have been scientifically validated, and (c) It is critical for the industry to maintain open communication and share data regarding pre-harvest interventions and GMP.
Harvest decontamination interventions (usually applied in multiple-hurdle systems) are more efficacious if the proportion of incoming cattle with E. coli O157:H7 on their hides is reduced. Cattle can be a reservoir for E. coli O157:H7 (Chapman et al., 1993) and these organisms can be transferred from hide to meat during slaughtering/dressing (Sofos et al., 1999) such that hides of animals being harvested can be a significant source of contamination of resulting carcasses (Riddell and Kerkeala, 1993; Bell, 1997; Sofos et al., 1999; Byrne et al., 2000; McEvoy at al., 2000). According to Ransom et al. (2003), carriage of E. coli O157:H7 on pre-evisceration carcasses was 7.1% if pre-harvest fecal prevalence was less than 20%, versus 12.5% if pre-harvest fecal prevalence was greater than 20%. Cattle hides may become contaminated with E. coli O157:H7 from feedlot pen floors (Dewell et al., 2003), contact between animals after departure from the farm (Tutenel et al., 2003), floors of lairage pens, or the stunning-box floor (Avery et al., 2002; Small et al., 2002, 2003).
Several studies have examined causality of carcass contamination at steps in the harvest process (Grau, 1987; Gill et al., 1996a, b; Bell, 1997; Gill and McGinnis, 1999), but such studies do not directly link sources with the introduction of specific organisms in terms of contamination events (Barkocy-Gallagher et al., 2001). Pulsed-field gel electrophoresis (PFGE) genotyping is used most notably by the Centers for Disease Control and Prevention, among others, to track sources of E. coli O157:H7 outbreaks.
Barkocy-Gallagher et al. (2001) were the first to use PFGE genotyping to track E. coli O157 on carcasses and in the slaughter environment and characterized the isolated E. coli O157 strains by use of PFGE in order to detect contamination routes. In the latter study, molecular characterization of E. coli O157:H7 (PFGE profiles and Stx types) was used to later determine that hide-to-hide contamination after departure from the farm seemed to be a major transmission route (Tutenel et al., 2003).
The stated objectives for this work were: As a prelude to identifying potential pre-harvest interventions, determine the origin (feedlot, transport trailers, packing-plant holding pens, or self-contamination from feces) of E. coli O157:H7 contamination on steer/heifer hides at the time of harvest.
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