Viridans streptococci

Membership includes Streptococcus mutans and sanguinis, the principal agents of dental caries and of subacute endocarditis; S. mitis and salivarius, which cause bacteraemia in neutropenic patients, sometimes with a septic shock syndrome and ARDS after chemotherapy-induced mucositis; and the S. anginosus (milleri) group, which is notable for pyogenic abscess formation in brain, liver, lung, and abdomen rather than endocarditis. Because these organisms are commensals, a single positive blood culture may represent contamination, whereas persistently positive cultures from separate sites satisfy a major Duke criterion for infective endocarditis. Endocarditis caused by them is subacute, occurring on previously abnormal valves, in contrast to Staphylococcus aureus, which attacks normal valves acutely and is the leading cause overall and in intravenous drug use, and Staphylococcus epidermidis, which infects prosthetic valves. Culture-negative endocarditis suggests HACEK organisms, Coxiella, or Bartonella. Antibiotic prophylaxis before dental work is now limited to high-risk cardiac conditions.