Binding of fibronectin to the surface of group A, C, and G streptococci isolated from human infections

Sixty-nine haemolytic and non-haemolytic streptococcal strains were isolated from various human infections and serogrouped with the coagglutination test. The amount of¹²⁵I-fibronectin bound to bacterial cells in a standard assay was determined. Most of the group A, C, and G strains were able to bind fibronectin. None of the group B or D strains bound significant amounts of fibronectin. Group A, C, and G streptococci appear to preferentially bind the N-terminal region of the fibronectin molecule because the 25K N-terminal fragment of the protein could effectively inhibit the binding of¹²⁵I-fibronectin to cells. Furthermore, the ability of representative strains of group A, C, and G to bind fibronectin was markedly reduced after trypsin treatment of the cells. Fibronectin binding components released from one strain by trypsin treatment inhibited the binding of¹²⁵I-fibronectin to all group A, C, and G streptococci strains. These findings indicate similarities among fibronectin binding proteins of the three groups of streptococci tested. However, the relative susceptibility to trypsin of fibronectin receptors of the three strains differed as did the relative potency of the inhibitory activity of receptors solubilized from different strains. Binding of fibronectin to the cell surface of group A, C, and G streptococci may contribute to virulence, for instance by promoting specific attachment to exposed fibronectin in open wounds and tissue lesions.