Characterization of Staphylococcus aureus-platelet binding by quantitative flow cytometric analysis.

Quantitative analyses of Staphylococcus aureus binding to platelets were done using flow cytometry after bacterial exposure to the following treatments: proteases (trypsin, protease K), antibiotics (oxacillin, gentamicin), surface carbohydrate modifiers (sodium periodate, anticapsular antibody), or platelet microbicidal protein. In separate studies, platelets were exposed to a monoclonal antibody to their Fc receptor (Fc gamma RII) before binding was quantified. The percentage of bacteria bound to platelets varied significantly among strains (22.1% +/- 3.8% to 76.4 +/- 3.2%). For all isolates, binding to platelets was rapid, saturable, and reversible, suggesting a receptor-ligand interaction. The following modifiers significantly reduced binding: platelet microbicidal protein (by 32.1% +/- 5.2%; P less than .001), homologous (but not heterologous) anticapsular antibody (by 17.7% +/- 1.9%; P less than .05), sodium periodate (by 36.3% +/- 4.3%; P less than .005), and anti-platelet Fc monoclonal antibody (by 41.5% +/- 4.4%; P less than .002). Collectively, these data suggest that the mechanism(s) involved in S. aureus-platelet binding are complex and multimodal, involving carbohydrate-rich and platelet microbicidal protein-susceptible S. aureus surface ligands as well as the platelet Fc receptor.