203 - Streptococcus anginosus Group

Abstract

The Streptococcus anginosus (milleri) group is a subgroup within the viridans-group streptococci that includes three separate streptococcal species: S. anginosus, S. constellatus, and S. intermedius. These viridans-group streptococci are part of the normal microbiota in the human oropharynx and urogenital and gastrointestinal tracts and initially were associated with dental abscesses. When pathogenic, the members of the S. anginosus (milleri) group are characterized by their proclivity to cause abscesses and should be considered true pathogens when isolated from blood cultures or other clinically relevant cultures. Like other streptococci, these gram-positive cocci are catalase negative and nonmotile. Their hemolysis patterns on sheep-blood agar are highly variable and include α-, β-, and γ-hemolytic patterns. Biochemically, S. anginosus (milleri) group streptococci are identified through use of three rapid biochemical tests: Voges-Proskauer test for acetoin production, arginine hydrolysis, and failure to ferment sorbitol. Clinically, S. anginosus (milleri) group infections frequently cause polymicrobial abscesses in both adults and children. Mixed infections are more invasive and frequently cause metastatic infection. The most frequent infections encountered are oral, head and neck, thoracic, and abdominal infections; metastatic abscesses such as brain or liver abscess or empyema may occur. Bacteremia caused by S. anginosus (milleri) group isolates suggests surgical sepsis; the source should be sought. Brain abscesses caused by members of the anginosus group should also prompt a search for a source. These abscesses or empyema often require surgical drainage. Cephalosporin antibiotics such as ceftriaxone continue to be effective, although additional coverage for anaerobic copathogens and surgical débridement and drainage may be needed.