Summary
S. aureus produces and secretes a protein, extracellular fibrinogen binding protein (Efb),
which contributes to virulence in wound infection. We have shown here that Efb is
a potent inhibitor of platelet aggregation. Efb can bind specifically to platelets
by two mechanisms; 1) to fibrinogen naturally bound to the surface of activated platelets
and 2) also directly to a surface localized component on the platelets. This latter
binding of Efb is independent of fibrinogen. The specific binding of Efb to the putative
receptor on the platelet surface results in a stimulated, non-functional binding of
fibrinogen in a dose dependent manner, distinct from natural binding of fibrinogen
to platelets. The natural binding of fibrinogen to GPIIb/IIIa on activated platelets
could be blocked by a monoclonal antibody against this integrin, whereas the Efb-mediated
fibrinogen binding could not be blocked. The enhanced Efb-dependent fibrinogen binding
to platelets is of a nature that does not promote aggregation of the platelets; instead
it inhibits aggregation. The anti-thrombotic action of Efb may explain the effect
of Efb on wound healing, which is delayed in the presence of Efb.
Keywords
Bacteria - coagulation inhibitors - fibrinogen / fibrin - platelet physiology
