Which organism is described as the most common cause of endocarditis in this material?

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Streptococcus viridans is the most common cause of endocarditis in settings where the valve is already damaged or abnormal and infection follows dental care or poor dentition. These bacteria are part of the normal oral flora and can enter the bloodstream during dental procedures. They have strong adherence to damaged endocardial surfaces via dextran-mediated binding to fibrin-platelet vegetations, leading to a subacute, indolent course rather than an abrupt, fulminant illness. This pattern contrasts with Staphylococcus aureus, which often causes rapid, acute endocarditis, especially in IV drug users or nosocomial settings, and with Enterococcus faecalis or Streptococcus bovis, which are associated with urinary/GI procedures or colon pathology, respectively. Thus, the described most common cause in this material is viridans group streptococci.