Acetylsalicylic acid reduces vegetation bacterial density, hematogenous bacterial dissemination, and frequency of embolic events in experimental Staphylococcus aureus endocarditis through antiplatelet and antibacterial effects

Background-Platelets are integral to cardiac vegetations that evolve in inf ectious endocarditis. It has been postulated that the antiplatelet aggregat ion effect of aspirin (ASA) might diminish vegetation evolution and embolic rates. Methods and Results-Rabbits with Staphylococcus aureus endocarditis were gi ven either no ASA (controls) or ASA at 4, 8, or 12 mg . kg(-1) . d(-1) IV f or 3 days beginning 1 day after infection. Vegetation weights and serial ec hocardiographic vegetation size, vegetation and kidney bacterial densities, and extent of renal embolization were evaluated. In addition, the effect o f ASA on early S aureus adherence to sterile vegetations was assessed. In v itro, bacterial adherence to platelets, fibrin matrices, or fibrin-platelet matrices was quantified with either platelets exposed to ASA or S aureus p reexposed to salicylic acid (SAL), ASA at 8 mg . kg(-1) . d(-1) (but not at 4 or 12 mg . kg(-1) . d(-1)) was associated with substantial decreases in vegetation weight (P<0.05), echocardiographic vegetation growth (P<0.001), vegetation (P<0.05) and renal bacterial densities and renal embolic lesions (P<0.05) versus controls, Diminished aggregation resulted when platelets w ere preexposed to ASA or when S aureus was preexposed to SAL (P<0.05). S au reus adherence to sterile vegetations (P<0.05) or to platelets in suspensio n (P<0.05), fibrin matrices (P<0.05), or fibrin-platelet matrices (P<0.05) was significantly reduced when bacteria were preexposed to SAL, Conclusions-ASA reduces several principal indicators of severity and metast atic events in experimental S aureus endocarditis. These benefits involve A SA effects on both the platelet and the microbe.