Role of Staphylokinase in the Acquisition of Plasmin(ogen)-Dependent Enzymatic Activity by Staphylococci

In this study, the role of the staphylococcal plasminogen activator, staphylokinase (SAK), was analyzed for its ability to mediate acquisition of cell-associated plasmin-like activity by staphylococci in the presence of a source of human plasminogen. A panel of staphylococcal strains isolated from humans was tested for the presence of the SAK gene, secretion of the plasminogen activator, and the ability to acquire enzymatic activity when incubated with purified human plasminogen or serum. When SAK was compared with the eukaryotic plasminogen activators, urokinase and tissue plasminogen activator, only SAK could mediate acquisition of cell-associated enzymatic activity by staphylococci without first generating significant fluid-phase plasmin. These studies provide evidence for a novel mechanism by which SAK-producing S. aureus can acquire an unregulatable host plasmin-like activity that might contribute to their invasive potential.