ABSTRACT
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. “Streptococcus milleri” is an unofficial name that has been applied to a group of streptococci which, although basically similar, show various hemolytic, serological, and physiological characteristics. Head and neck infections and pneumonia are most often associated with beta-hemolytic strains, and bacteremia and gastrointestinal and urogenital tract infections with alpha-hemolytic strains. The species name Streptococcus anginosus has recently been recognized as the approved name for these organisms. Streptococci known as S. milleri have been implicated as etiologic agents in a variety of serious purulent infections, but because of their heterogeneous characteristics, these organisms may be unrecognized or misidentified by clinical laboratories.
