11 - Sources of microbial contamination at slaughtering plants

Abstract

The production of red meats at slaughtering plants involves the slaughtering of animals, carcass dressing, cooling of meat, and carcass breaking. Slaughtering processes usually include stunning and always include sticking and bleeding of the animal. Other operations, such as electrical stimulation of the carcass to accelerate the development of rigor, might also be performed. Bacteria could be introduced into the carcass through the stunning or sticking wounds, possibly passing to the muscle tissues. When that possibility was investigated, it was found that bacteria from slaughtering instruments could be recovered from muscle tissues only when instruments like pithing rods were artificially contaminated with very large numbers of bacteria before they were applied to the animal. Thus, contamination of meat with bacteria during slaughtering operations could occur under only highly unusual circumstances and the muscle tissues of animals are generally sterile until meat surfaces are contaminated during carcass dressing. While pathogenic bacteria can certainly be transferred to meat in contaminated feces during the carcass dressing process, fecal matter may not be the only or even the major source of the enteric pathogens on the raw meat products dispatched from every packing plant. Thus proximate sources of pathogenic organisms other than fecal matter must be considered and properly investigated at packing plants if the contamination of raw meats with pathogens is to be minimized. This chapter focuses on the sources of microbial contamination at slaughtering plants.