Identification of a Staphylococcus aureus adhesin that mediates adherence to human endothelial cells

The frequency with which S. aureus infects or invades endovascular tissue suggests that a unique bacterial-endothelial cell interaction is involved. In the present study, intact human umbilical vein endothelial cells (EC) were used to identify and follow the sequential purification of a staphylococcal adhesin that mediates adherence to EC. Lysostaphin-solubilized S. aureus proteins were separated on an SDS-PAGE gel, transferred to polyvinylidene difluoride (PVDF), probed with biotin-labelled EC and then visualized with streptavidin alkaline phosphatase. Scanning electron microscopy confirmed that the EC remained intact on the PVDF. A 120 kDa surface adhesin recognized by the EC was isolated from two staphylococcal strains. Partially purified protein (50 fold enriched) from both strains inhibited S. aureus adherence to EC in a competitive inhibition assay (100 μg/well, >1000x reduction, p<.05). Purified protein (500ng/ml) eluted from a gel, resulted in a >10x reduction in bacterial adherence to EC (p<.05). A similar size protein was present in 13 additional S. aureus strains tested, but not in 5 other bacterial species. The 120 kDa protein is equally expressed during logarithmic and stationary growth phase. It is not secreted into the media. The protein interacted with biotinylated bovine mammary cells or human foreskin fibroblasts suggesting that the host cell receptor is a common determinant. The ability of S. aureus to cause metastatic disease in different tissues may depend on the ability of this adhesin to recognize common cellular epitopes. This 120 kDa protein may play a critical role in the first step involving staphylococcal colonization of endovascular tissue.