A ROLE FOR FIBRINOGEN IN THE STREPTOKINASE-DEPENDENT ACQUISITION OF PLASMIN(OGEN) BY GROUP-A STREPTOCOCCI

Acquisition of plasmin(ogen) by group A streptococci occurs by two distinct pathways. In addition to the well-characterized direct interaction of plasmin with cell-surface receptors on group A streptococci, a second pathway dependent on streptokinase and a nonplasminogen factor(s) present in human plasma was identified. The role of streptokinase in the second pathway was not merely as a plasminogen activator, since substitution of the plasminogen activator urokinase did not result in the capture of plasmin(ogen) by bacteria in the presence of plasminogen-depleted plasma. However, if streptokinase was added to plasmin that had been generated by treatment of plasminogen with urokinase, the ability of the bacteria to capture plasmin in the presence of plasminogen-depleted plasma was restored. Fibrinogen present in human plasma was identified as the major factor required for streptokinase-dependent uptake of plasmin(ogen) by group A streptococci.