Occurrence and pathogenicity of the Streptococcus milleri group.

Streptococci of the milleri group are part of the normal flora of human mucous membranes. These streptococci have also been reported to be significant pathogens. Like other mucosal streptococci, they may cause infective endocarditis; unlike other mucosal streptococci, however, they have also been repeatedly associated (more frequently in men than in women) with serious suppurative infections. Evidence for the pathogenicity of the Streptococcus milleri group is scattered and mainly circumstantial. Although the organisms are found in a high proportion of certain suppurative infections, other bacteria are often present as well. Successful treatment of these infections with surgery and broad-spectrum antibiotics is not indicative of any specific etiology. Only a few attempts at the induction of experimental infections other than endocarditis have been effective. Further investigation is required to establish the pathogenicity and pathogenic mechanisms of the S. milleri group.