In bloodborne staphylococcal infections, bacteria and platelets often combine, forming thrombi on the subendothelium, 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.

Receptor-mediated adhesion of bacteria to biological surfaces is a significant step leading to infection. Due to an increase in bacterial antibiotic resistance, novel methods to block and disrupt these specific interactions have gained considerable interest as possible therapeutic strategies. Recently, several monoclonal antibodies specific for the Staphylococcus aureus collagen receptor demonstrated specialized ability to displace attached cells from collagen in static assays. In this study, we experimentally examine the monoclonal antibody detachment functionality under physiological shear conditions to evaluate the role of this parameter in the detachment process. The detachment of staphylococci from collagen was quantified in real-time using a parallel plate flow chamber, phase contrast video-microscopy and digital image processing. The results demonstrate a unimodal dependence of detachment on fluid wall shear rate. The observed decrease in effective detachment rate with increasing force at the highest shear levels evaluated is counterintuitive and has not been previously demonstrated. Several possible mechanisms of this result are discussed.

Dynamic bacterial adhesion has recently gained significant attention due to its role in the initiation of infectious diseases. Staphylococcus aureus binding to collagen has been shown to be an important event in the pathogenesis of infection. Staphylococcal strains have exhibited wide variability in their level of collagen binding, which may be a result of the collagen receptor expression level. In this study, the dynamic adhesion to collagen for several S. aureus strains was quantified at physiological wall shear rates in a parallel-plate flow chamber. In addition, the collagen receptor density was quantified for each strain. An existing theoretical framework was used to analyze the dependence of adhesion on receptor density. Intrinsic kinetic adhesion parameters were determined and demonstrated to be strong functions of receptor density for all strains. These results suggest that staphylococcal adhesion to collagen is heavily dependent on the receptor density. Using this analytical approach it is possible to predict the dynamic adhesion of S. aureus to collagen in vitro by only measuring the collagen receptor density.