AN APPRAISAL OF THE VIRULENCE FACTORS ASSOCIATED WITH STREPTOCOCCAL ENDOCARDITIS

Platelet aggregation is believed to be a virulence factor in infective endocarditis. Other factors may be adhesion to components of thrombot ic vegetations, particularly platelets, fibronectin and fibrinogen. Tw o strains from the Streptococcus sanguis group (SSG) were chosen for c omparative study on the basis that one aggregated both human and rat p latelets and the other lacked this capacity. Both strains caused endoc arditis in the rat model but the aggregating strain was found in highe r numbers in the excised vegetations. The nonaggregating strain was un able to bind to human or rat platelets but could bind insoluble fibron ectin, insoluble fibrinogen and platelet-fibrin clots from both source s, albeit to a lesser extent than the aggregating strain. These result s suggest that whereas adhesion to, and aggregation of, platelets are not essential events in the initiation of the pathogenesis of experime ntal endocarditis, they may be factors contributing to virulence.