Quantification of staphylococcal-collagen binding interactions in whole blood by use of a confocal microscopy shear-adhesion assay

In bloodborne staphylococcal infections, bacteria and platelets often combine, forming thrombi on the sub-endothelium, where collagen is exposed. In this process, the collagen serves as a potential binding surface for Staphylococcus aureus. However, the extent and importance of S. aureus-collagen binding interactions in the development of infected thrombi is uncertain. We quantified S. aureus adhesion to collagen in a whole-blood suspension under defined physiologically relevant fluid shear conditions. S. aureus-collagen binding interactions, mediated by both the S. aureus collagen adhesin (CNA) and protein A-von Willebrand factor (vWf), were evaluated using mutant strains and antibody-blocking techniques. The position of adherent bacteria (at the collagen surface or above the surface in the platelet aggregate) was measured using confocal laser microscopy. Results demonstrated significant CNA-collagen interactions and protein A-vWf-collagen binding interactions under physiological shear conditions. We conclude that collagen binding interactions are important in the development of infected thrombi.