Microbial Pathogens

Depending upon the microorganisms present in the product, microbial spoilage certainly may be a potential health hazard. The following microorganisms may be a health hazard in dairy products.

a. Clostridium botulinum. Dairy products are rarely involved in outbreaks of botulism since most dairy products are consumed in a fresh state rather than canned.

b. Salmonella Species. Raw milk has been the carrier in outbreaks throughout the world. One outbreak in the US was due to ingestion of pasteurized milk. Affected ice cream was, in most cases, contaminated by infected shell eggs. The risk of Salmonella organisms in dairy products is rather low.

c. Escherichia coli. Certain strains of E. coli may cause enteritis in humans. In 1971, an outbreak due to enteropathogenic E. coli in imported cheese resulted in several hundred reported cases. In other countries, outbreaks have been associated with consumption of dairy products. The symptoms of illness are diarrhea, fever, nausea, and cramps.

d. Staphylococcus Species. These organisms, especially S. aureus, may be present in the milk of cows suffering from acute mastitis. It is the most common pathogenic organism found in raw milk, but most cases of infection may be traced to a human carrier. Some organisms, especially the lactobacilli, inhibit the growth of staphylococci. Staphylococcal food poisoning has occurred through consumption of cheese which had not developed acidity in a normal manner. Evidently, the acid-producing bacteria, such as the lactobacilli, had not developed and were thus not available to inhibit the growth of contaminating staphylococci.

e. Mycobacterium bovis. Infected raw milk is the chief means by which milkborne tuberculosis is transmitted to man. The organism is one of the most heat-resistant of the nonspore-forming pathogenic bacteria, but fortunately it is destroyed by pasteurization. Milk-borne cases of tuberculosis are rare today. Such cases were more common when milk was not pasteurized and when tubercular cows were not eliminated from the herds.

f. Brucella Species. Brucellosis is the name applied to the disease caused by members of the group of organisms known as Brucella. This disease is spread by contact with infected material or by consumption of raw milk from diseased animals. Brucellosis is most commonly found in rural areas where raw milk is used. The causative organisms are destroyed easily when milk is pasteurized.

g. Leptospira Species. Leptospirosis is a spirochetal infection. Mild attacks in man resemble influenza. Leptospira organisms have been found in the milk of diseased cows. There is some doubt that such milk is a source of the disease in man. As milk has a lytic action on the organisms, they are gradually disintegrated.

h. Coxiella burnetii. This organism causes Q fever, a pneumonia-like disease of rickettsial origin. The organism has been isolated from raw milk. Butter made from unpasteurized milk has also been found to be a source of the disease. This organism is one of the organisms most resistant to pasteurization. Therefore, proper relationships of time and temperature must be carefully observed to ensure its destruction.

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