The pathogenesis of a high-virulence and a low-virulence strain of Corynebacterium bovis in the mammary gland of the mouse.

A comparison was made of the pathogenesis of experimental mastitis in mice caused by a strain of Corynebacterium bovis (P3) isolated from clinical mastitis in the cow and a strain (NCDO 1930) isolated from the teat of a symptomless carrier cow. Strain NCDO 1930 elicited a neutrophil response which controlled the infection so that, after 6 to 8 days, 9 of 10 glands were sterile and one abscess was found. In contrast, the neutrophil response to strain P3 failed to control the infection and, by 6 to 8 days, 8 of 10 glands were infected and there were abscesses in 11 of 20 glands. The virulence of strain P3 was associated with its ability to colonize on and in milk fat globules, from which the organisms multiplied in the alveolar lumen irrespective of the neutrophil infiltration.