Streptococcus mitis

S. mitis colonizes the oral mucosa and dental plaque. Its distinctive clinical niche is the patient rendered neutropenic and mucositic by cytotoxic chemotherapy, particularly high-dose cytarabine for acute leukaemia or after haematopoietic stem cell transplantation: breakdown of the oral mucosal barrier permits invasion, and the resulting viridans streptococcal shock syndrome causes fever, hypotension, rash, and acute respiratory distress with a mortality that can exceed that of gram-negative sepsis. This is one reason empirical febrile neutropenia regimens sometimes add vancomycin when mucositis is severe or when the patient is unstable, since penicillin resistance among these strains has risen. S. mitis is also a common cause of subacute native valve endocarditis, sharing the dextran-mediated valve adherence of the group, and is one of the organisms whose presence in a single blood culture may reflect skin or oral contamination, so repeated cultures matter. Laboratory identification rests on alpha-haemolysis with optochin resistance and bile insolubility, separating it from pneumococcus.