Section I. MICROBIOLOGY OF DAIRY PRODUCTS
a. General. It is important to apply the information learned about microbiology
in lesson one to food products used by the public. This lesson, Lesson 2, will discuss
food microbiology as it is related to dairy products, meats, poultry and shell eggs,
waterfoods, fruits, and vegetables.
b. Milk. Since milk contains proteins, carbohydrates, fats, vitamins, and
minerals, and has a pH of about 6.8, it is little wonder that in addition to being an
excellent food for man, it provides an excellent growth medium for microorganisms.
Some microorganisms can be harmful while others are beneficial when existing in milk.
The beneficial organisms, in most cases, are controlled and used to make other dairy
products. Harmful organisms can and must be kept to a minimal, safe level to prevent
DISEASES FROM MILK
a. Two Sources of Pathogenic Organisms. Nonpathogenic bacteria are
always found in milk even under the strictest sanitary conditions. However, milk also
provides an excellent media for the dissemination of pathogenic microorganisms. Milk
may become contaminated with pathogenic organisms anywhere along the line from
cow to consumer. This contamination may come from an infected cow or from an
infected milk handler. Therefore, we classify the occurrence of pathogenic organisms
as coming from two sources.
Organisms that infect the cow and, therefore, the milk.
(2) Organisms causing disease as a result of contamination of the milk by
b. Diseases Transmitted From the Cow. Included in the diseases occurring
as a result of organism contamination prior to or at time of lactation (that is, transmitted
from the cow) are tuberculosis, brucellosis (undulant fever), streptococcal infections,
some staphylococcal infections, and Q fever (rickettsial organisms). (A description of
these diseases can be found in any standard medical reference.) Tuberculosis and
undulant fever are the most important of these diseases. Both are transmittable from
animal to animal or from animal to man. The route from the animal's tissues to the milk
is not known for certain, but there is some possibility that Brucella organisms, which
cause undulant fever, may be secreted directly from the blood stream into the udder.
The infectious agent of bovine tuberculosis is the bacterium Mycobacterium bovis.