The ability of lactenin to prevent the multiplication of group A streptococci when milk becomes contaminated with that organism accounts in part at least, for the infrequency of milk-borne streptococcal epidemics. From epidemiological studies it has been shown that most such epidemics arise from the consumption of raw milk in which streptococci occur as a result of bovine mastitis due to group A streptococcus. Lactenin fails to prevent the establishment of mastitis due to the group A streptococcus because the milk in the cow's udder is at a low oxidation-reduction potential and the lactenin is inactive.

Lactenin, being destroyed by temperatures of 80°C. or above, is absent from canned and powdered milk. When the latter have been diluted or reconstituted, they can serve as excellent growth media for group A streptococci, and epidemics have occurred as a result of contamination of milk supplies of those types.

The administration of lactenin by mouth or intraperitoneal injection failed to protect mice from peritonitis or subcutaneous infection due to group A streptococcus.

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