Human milk taken by the baby straight from the mother is seldom a vector of pathogens. Only minor bacteriological problems are associated with the collection and storage of expressed human milk. Cow's milk, on the other hand, presents many important problems. It may contain pathogens derived from the cow; the circumstances of its collection, unless carefully controlled, permit it to become heavily contaminated with a wide variety of micro-organisms; it is a good culture medium for many of these; it may spend hours or days at temperatures suitable for bacterial multiplication before it is consumed; and, as the result of pooling, milk from a single cow may be distributed to a large number of human beings.
Organisms which may be present in cow's milk include the following:-
Multiplication of organisms can be kept to a minimum by cooling the milk as soon as it is collected, keeping it cool during transmission, and delivering it to the consumer early in the day while the atmospheric temperature is still low. But even a combination of all these measures does not guarantee that the milk will be safe to drink. This can be achieved only by heating it.
BACTERIOLOGICAL EXAMINATION OF MILK
In this test, haematoxylin-stained dead brucellae are added to a sample of the milk; if they are agglutinated, they rise up in the fat globules and form a blue ring in the cream layer. Milk products, such as butter and cheese, and milk-containing foods, such as ice-cream and custards, are of course liable to contain pathogens similar to those found in milk, and are exposed to greater risks of contamination by handlers. It is, however, very much more difficult to devise bacteriological standards and tests for these products, apart from cultures to exclude the presence of named pathogens.
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