The extracellular fibrinogen binding protein (Efb) belongs to the Secreted Expanded Repertoire Adhesive Molecules (SERAM) family of secreted proteins from Staphylococcus aureus. Efb binds both to fibrinogen and to complement C3. A knock-out mutant lacking Efb is less virulent in a rat wound infection model. Vaccination of mice with Efb followed by S. aureus infection (insertion of a piece of cloth contaminated with S. aureus) resulted in reduced signs of infection.

In addition to fibrinogen and complement binding, Fbe can bind to activated platelets in such a way that its aggregation is blocked. Therefore S. aureus infection of a wound results in delayed wound healing due to Efb. Efb given intravenously also leads to a prolonged bleeding time and can prevent thrombus formation in a mouse model of stroke.

Separate binding sites at both the C- and N-termini of Efb bind simultaneously to fibrinogen, thereby causing precipitation of Efb:fibrinogen complex. This presumably causes depletion of fibrinogen in the vicinity of the bacterium. Both fibrinogen-binding domains of Efb can inhibit clotting of fibrinogen by thrombin. Similarly, also other fibrinogen binding proteins from S. aureus inhibited clotting of fibrinogen (ClfA, and Eap) and Fbe (SdrG) from S. epidermidis.

Delayed wound healing due to Efb is thus due to a multitude of functions: 1) Inhibition of platelet aggregation, 2) Consumption of fibrinogen by co-precipitation, 3) Inhibition of clotting.