Analysis of plasmin(ogen) acquisition by clinical isolates of group A streptococci incubated in human plasma.

Group A streptococci isolated from throat swabs or blood cultures were compared for the expression of plasmin(ogen) receptors. The majority of isolates bound 125I-labeled Lys-plasmin and 125I-labeled Lys-plasminogen while displaying minimal reactivity with 125I-labeled Glu-plasminogen. All streptococcal isolates could acquire surface enzymatic activity when incubated in human plasma but not if the plasma had been depleted of plasminogen. The ability to acquire surface enzymatic activity was limited by the quantity of streptokinase in the reaction mixture. There was no statistically significant difference between group A streptococci isolated from throat swabs and those from blood cultures with respect to their interaction with components of the fibrinolytic system in human plasma. However, these isolates could be divided into two groups based on their ability to acquire surface enzymatic activity when incubated in plasma with exogenous streptokinase. Surprisingly, the acquisition of surface enzymatic activity when incubated in plasma containing streptokinase was not always correlated with the plasmin(ogen) binding capacity determined by direct binding of radiolabeled ligands. Analysis of this phenomenon suggests that group A streptococci can use diverse mechanisms to acquire plasmin(ogen)-dependent enzymatic activity.