Phenotypic characterization of Streptococcus dysgalactiae isolates from bovine mastitis by their binding to host...

The binding of 80 Streptococcus dysgalactiae mastitis isolates from 51 farms to plasma and connective tissue proteins fibronectin (29 kDa N-terminal fragment), vitronectin, collagen type I, fibrinogen, alpha 2-macroglobulin, IgG, and albumin was studied. All isolates boiund the bovine 29 kDa fibronectin fragment and the binding of bovine fibrinogen, caprine albumin, bovine alpha 2-macroglobulin-trypsin complexes and caprine IgG was also very frequent (92.5, 92.5, 72.5% and 87.5%, respectively). Binding to human vitronectin was observed in 55% of the isolates, whereas only 20% of the isolates bound human type I collagen. None of the isolates bound native alpha 2-macroglobulin. Nearly all isolates (91%) bound more than 3 ligands. The bacterial binding sites for these proteins (termed here receptors) occurred in different combinations of which the combination fibronectin-, albumin-, fibrinogen-, vitronectin-, alpha 2-macroglobulin- and IgG-receptor was the most common. More than one isolate was obtained from 10 farms. The isolates from 5 farms showed close similarity of binding profiles within the farm, indicating that they were of similar origin and suggesting that the binding characteristics were relatively stable. Wider variation among the isolates obtained from other 5 farms was detected. The different isolates of the same farm origin varied mostly in the binding of albumin, IgG and fibrinogen. Interestingly, a difference in the number of receptors between isolates from two different sampling areas was observed. The binding profiles offer a new phenotypic method for epidemiological studies and may also when combined with genetical studies provide more insight both into the role of the bacterial plasma and connective tissue protein receptors in the infection process and the regulation of receptor expression.