A Comparison of the Effects of Shear Stress on the Interactions between Streptococcus sanguis and Staphylococcus aureus with Perfused Human Blood Platelets

Abstract number: P0328

Kerrigan¹ SW, Douglas² CWI, Meade¹ G, Foster³ TJ, Cox¹ DM

¹¹Royal College of Surgeons in Ireland, Dublin, Ireland ¹¹Royal College of Surgeons in Ireland, Dublin, Ireland ²²University of Sheffield, Sheffield, UK ³³Trinity College Dublin, Dublin, Ireland

Infective endocarditis is a bacterial infected disease associated with considerable morbidity and mortality. Staphylococcus aureus and Streptococcus sanguis are frequent causative organisms. Platelet activation plays a critical role in the pathogenesis and dissemination of the infective process. Previously we identified a role for the S. aureus fibrinogen binding protein ClfA and S. sanguis GPIba binding protein, Hsa, in supporting platelet adhesion and inducing an aIIbb3 dependent platelet aggregation. We therefore, investigated the influence of shear stress on bacteria-platelet interactions. Bacteria were coated onto flow chamber glass cover slips overnight at room temperature. Platelets in whole blood were stained with a lipophillic dye. Whole blood was perfused over the bacteria at a flow rate of 50 s^-1 to 1500 s^-1. Experiments were recorded in real time and visualized using fluorescence and brightfield microscopy. Deletion mutants were generated by allelic exchange with antibiotic resistance cassettes. Platelets rolled on immobilised S. sanguis at a low shear rate of 50 s^-1 however, failed to interact at the higher shear rate of 200 s^-1 or above. Platelets failed to interact with a Hsa deletion mutant of S. sanguis, at any shear rate. Furthermore, platelets failed to interact with S. aureus at a shear rate of <500 s^-1. However, platelets time dependently adhered to S. aureus at a higher shear rate of 800 s^-1 and 1500 s^-1. Platelets failed to interact with a ClfA deletion mutant of S. aureus at any shear rate. Our results demonstrate for the first time that S. sanguis interacts with platelets under low shear conditions (veneous pressure) and S. aureus interacts with platelets under high shear conditions (arterial pressure). Furthermore, our results identify surface proteins essential for the interaction with platelets. These results may lead to new insights into potential new drug targets for patients with infective endocarditis.