Multiplication of Staphylococci in vitro in normal and mastitic milk from vaccinated and nonvaccinated cows.

Mastitis was induced by injection of cell walls of Staphylococcus aureus into the mammary glands of normal cows and of cows which had been vaccinated parenterally with a staphylococcal bacterin in adjuvant. Multiplication of S aureus in normal milk and in mastitic milk from vaccinated and nonvaccinated cows was determined in constant volume cultures. Growth was significantly inhibited during the 1st 6 hours of incubation, regardless of the nature of the milk or the vaccination status of the cows. Growth was inhibited for 24 hours in normal milk, and the organisms grew exponentially in mastitic milk regardless of the vaccination status of the cows.