Invasion of bovine mammary epithelial cells by Streptococcus dysgalactiae

Two strains of Streptococcus dysgalactiae, isolated from cows with mastitis, were assayed for their ability to invade, multiply, and induce damage to a bovine mammary epithelial cell line, MAC-T. Invasion of S. dysgalactiae into MAC-T cells was time-dependent, and invasion was inhibited in a dose-dependent manner by cytochalasin B and D, but not by colchicine. The invasion process did not appear to affect viability of mammary epithelial cells, but cellular damage was induced, as indicated by a time-dependent release of increasing amounts of lactate dehydrogenase. No net intracellular bacterial growth was observed, but S. dysgalactiae survived inside MAC-T cells. These results indicated that S. dysgalactiae invaded epithelial cells, induced cellular damage, and was capable of persisting inside bovine mammary epithelial cells.