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A Guide to Food Pathogens

A Guide to Food Pathogens

The Culinary Institute of America

The specific types of pathogens responsible for foodborne illnesses are fungi, viruses, parasites, and bacteria.

Fungi, which include molds and yeast, are more adaptable than other microorganisms and have a high tolerance for acidic conditions. They are more often responsible for food spoilage than for food-borne illness. Fungi are important to the food industry in the production of cheese, bread, wine, and beer.

Viruses do not actually multiply in food, but if through poor sanitation practice a virus contaminates food, consumption of that food may result in illness. Infectious hepatitis A, caused by eating shellfish harvested from polluted waters (an illegal practice) or poor hand-washing practices after using the rest room, is an example. Once in the body, viruses invade a cell (called the host cell) and essentially reprogram it to produce more copies of the virus. The copies leave the dead host cells behind and invade still more cells. The best defenses against food-borne viruses are good personal hygiene and obtaining shellfish from certified waters.

Parasites are pathogens that feed on and take shelter in another organism, called a host. The host receives no benefit from the parasite and, in fact, suffers harm or even death as a result. Amebas and various worms, such as Trichinella spiralis, which is associated with pork, are among the parasites that contaminate foods. Different parasites reproduce in different ways. An example is the parasitic worm that exists in the larva stage in muscle meats. Once consumed, the life cycle and reproductive cycle continue. When the larvae reach adult stage, the fertilized female releases more eggs, which hatch and travel to the muscle tissue of the host, and the cycle continues.

Bacteria are responsible for a significant percentage of biologically caused food-borne illnesses. In order to better protect food during storage, preparation, and service, it is important to understand the classifications and patterns of bacterial growth.

Bacteria are classified by their requirement for oxygen, the temperatures at which they grow best, and their spore-forming abilities. Aerobic bacteria require the presence of oxygen to grow. Anaerobic bacteria do not require oxygen and may even die when exposed to it. Facultative bacteria are able to function with or without oxygen.

Bacteria reproduce by means of fission—one bacterium grows and then splits into two bacteria of equal size. These bacteria divide to form four, the four form eight, and so on. Under ideal circumstances, bacteria will reproduce every twenty minutes or so. In about twelve hours, one bacterium can multiply into sixtyeight billion bacteria, more than enough to cause illness.

Certain bacteria are able to form endospores, which serve as a means of protection against adverse circumstances such as high temperature or dehydration. Endospores allow an individual bacterium to resume its life cycle if favorable conditions should recur.