Influence of Streptococcus dysgalactiae surface hydrophobicity on adherence to mammary epithelial cells and phagocytosis by mammary macrophages

Bacterial surface hydrophobicity (SH) plays a role in adhesion of bacteria to host surfaces and ingestion by phagocytic cells. Streptococcus dysgalactiae (n = 60) isolated from bovine intramammary infections were examined for expression of SH after growth in Todd-Hewitt broth (THB) and THB supplemented with skim milk, whey, lactose, and casein. Strains were significantly more hydrophobic after growth in THB and THB plus whey and more hydrophilic after growth in THB plus skim milk. Both trypsin and proteinase K abolished SH in three strains tested. Mild pepsin treatment had little effect on SH, while heat treatment at 70 degrees or 80 degrees C abolished SH in two strains tested. A hydrophilic strain of S. dysgalactiae did not adhere as well to bovine mammary epithelial cells as a hydrophobic strain. Trypsin treatment significantly reduced adherence of a hydrophobic strain of S. dysgalactiae to epithelial cells while adherence of a hydrophilic strain remained unaltered. A hydrophilic strain of S. dysgalactiae was significantly more resistant to phagocytosis by bovine mammary gland macrophages than a hydrophobic strain. Differences in expression of SH may play an important role in determining the ability of S. dysgalactiae to establish successfully within the mammary gland.