The Multiplication of Staphylococci of Bovine or Human Origin in Cows’Milk

Abstract

Summary Mild mastitis was produced experimentally in cows of various ages, stages of lactation and milk yields, by the infusion of staphylococcal culture filtrate into the teat canal. The multiplication in vitro of Staphylococcus aureus strain 280 in samples of mastitis milk from these cows was compared with the multiplication of the same organism in normal milk from the same cows. When the leucocyte count in the mastitis milk was greater than 1.0 X 106 cells/ml., there was inhibition of staphylococcal multiplication, although above this level the degree of inhibition produced by the milk of different cows was variable, and not directly related to the magnitude of the leucocyte counts. In milk from a single cow, a linear relationship between the leucocyte:bacteria ratio and the inhibitory index for strain 280 was demonstrated. Significant differences in multiplication rates in normal milk were not observed among 10 strains of staphylococci of bovine origin and 5 of human origin. While each strain was inhibited to a significant extent in mastitis milk, there was some variation among the strains. The inhibitory index of the mastitis milk for the bovine strains was usually somewhat greater than that for strain 280, while the multiplication of the human strains was inhibited less than that of strain 280. The multiplication rate of strain 280 in either normal or mastitis milk from each of 3 cows was slightly slower under anaerobic than under aerobic conditions.