PLG and infection: Streptokinase (Ska) is highly specific for human plasminogen and contributes to streptococcal virulence by generating plasmin, which leads to bacterial spread from a primary focus of infection by causing fibrinolysis, as well as degradation of the extracellular matrix and basement membrane components.23 The isoleucine or threonine residues at position 17 of the Ska sequence of emm89 strains are located in the streptokinase α domain.