Streptokinases produced by pathogenic group C streptococci demonstrate species-specific plasminogen activation.

The species specificities of plasminogen activation and binding of plasmin by pathogenic group C streptococci isolated from humans, horses, and pigs were examined. Of 56 streptococcal isolates, 52 elaborated plasminogen activator activity and 49 of these had specificity for plasminogen of the homologous host. Analysis of supernatants from 13 isolates indicated that the plasminogen activator activity resulted from secreted streptokinases. These 13 streptokinases were antigenically related and bound all three plasminogens, indicating that the binding recognition sites were conserved despite the observed species-specific activation. In addition, all group C isolates tested demonstrated surface receptors that bound human, equine, and porcine plasmin. Species-specific plasminogen activation may be an early step in events resulting in infection and may account for the species preference of certain streptococci.