C
The primary causes of infective endocarditis are the viridans streptococci, made up of several species (Box 67-2). These organisms are normal inhabitants of the oral cavity, often gaining en-trance to the bloodstream as a result of gingivitis, periodontitis, or dental manipulation. Heart valves, especially those previously damaged, present convenient surfaces for attachment of these bacteria. Streptococcus sanguinis and S. mutans are frequently isolated in streptococcal endocar-ditis.