Differential binding of biofilm-derived and suspension-grown Staphylococcus aureus to immobilized platelets in shear flow

Background. The adhesion of Staphylococcus aureus to platelets is a critical first step in endovascular infection. S. aureus is known to form biofilms and detached cells are likely responsible for initiating bloodborne secondary infections. Although several previous studies have evaluated the mechanisms of S. aureus-platelet binding, standard procedures have used suspension-grown cells, which are known to differ in their adhesion properties from biofilm-derived cells. Methods. This study used both shake flask-grown cells (hereafter, "suspension-grown cells") and cells derived from growing biofilms to compare the level and mechanisms of adhesion to immobilized platelets under physiologically relevant shear conditions. Of specific interest were the roles of clumping factor A (ClfA) and plasma proteins in supporting adhesion. Results. S. aureus cells collected after 24 h of biofilm growth demonstrate significantly reduced levels of binding to immobilized platelets in the presence of exogenous plasma proteins, in comparison with suspension-grown cells. These adhesion results correlate directly with ClfA expression levels for the different cell populations. Conclusions. The results presented herein demonstrate that the mode of growth, temporal adhesin expression pattern, and hydrodynamic shear govern S. aureus adhesion to immobilized platelets. ClfA was identified as the critical binding adhesin, regardless of the mode or phase of growth.