Research letterInteraction between fibronectin and purified staphylococcal clumping factor

Clumping of Staphylococcal aureus was observed in the presence of fibrinogen as well as fibronectin. In order to elucidate the mechanism of this clumping, binding of radiolabelled fibrinogen and fibronectin to S. aureus cultures was studied. Cultures of S. aureus reacted with 125I-labelled fibrinogen as well as fibronectin. The binding of labelled fibrinogen to S. aureus could be completely inhibited by unlabelled fibronectin, whereas the binding of labelled fibronectin was only partially inhibited by unlabelled fibrinogen. This suggested an interaction of fibronectin with clumping factor which is the binding protein for fibrinogen in staphylococci. The clumping factor was purified from S. aureus strain K 807 by affinity chromatography on fibrinogen-Sepharose followed by HPLC. The purified clumping factor inhibited the binding of fibrinogen and fibronectin to staphylococci. In western blots the purified clumping factor reacted with fibrinogen as well as fibronectin. Thus, the direct interaction of clumping factor with fibronectin might be responsible for the clumping of staphylococci in fibrinogen depleted plasma or serum.