It is generally agreed that the internal tissues of healthy slaughter animals are free of bacteria at the time of slaughter, assuming that the animals are not in a state of exhaustion. When one examines fresh meat and poultry at the retail level, varying numbers and types of microorganisms are found. The following are the primary sources and routes of microorganisms to fresh meats with particular emphasis on red meats: 1.
The stick knife. After being stunned and hoisted by the hind legs, animals such as steers are exsanguinated by slitting the jugular vein with what is referred to as a “stick knife.” If the knife is not sterile, organisms are swept into the bloodstream, where they may be deposited throughout the carcass. 2. Animal hide.
Organisms from the hide are among those that enter the carcass via the stick knife. Others from the hide may be deposited onto the dehaired carcass or onto freshly cut surfaces. Some hide biota becomes airborne and can contaminate dressed out carcasses as noted below. See the section on carcass sanitizing and washing towards the end of this chapter. 3.
Gastrointestinal tract. By way of punctures, intestinal contents along with the usual heavy load of microorganisms may be deposited onto the surface of freshly dressed carcasses. Especially important in this regard is the paunch or rumen of ruminant animals, which typically contains ∼1010 bacteria per gram. 4.
Hands of handlers. As noted in Chapter 2, this is a source of human pathogens to freshly slaughtered meats. Even when gloves are worn, organisms from one carcass can be passed on to other carcasses. 5. Containers. Meat cuts that are placed in nonsterile containers may be expected to become contaminated with the organisms in the container. This tends to be a primary source of microorganisms to ground or minced meats. 6. Handling and storage environment.
Circulating air is not an insignificant source of organisms to the surfaces of all slaughtered animals; this is noted in Chapter 2. 7. Lymph nodes. In the case of red meats, lymph nodes that are usually embedded in fat often contain large numbers of organisms, especially bacteria. If they are cut through or added to portions that are ground, one may expect this biota to become prominent.