The Streptococcus bovis/Streptococcus equinus complex was created in 2003 after an extensive taxonomic revision . This complex includes four major species (table 1) that all belong to group D streptococci (GDS). The published literature regarding these organisms does not always distinguish GDS to the biotype and/or subspecies level consistently.
The microbiology, pathogenesis, and epidemiology of these species will be reviewed here. The clinical manifestations, diagnosis, and treatment are discussed separately. (See "Clinical manifestations, diagnosis, and treatment of infections due to group D streptococci (Streptococcus bovis/Streptococcus equinus complex)".)
Group D streptococci (GDS) are catalase-negative, gram-positive cocci that usually express the Lancefield group D antigen. Colonies are typically small and non-hemolytic on blood agar. Most GDS grow in 40 percent bile and hydrolyze esculin [2-4]. GDS can be distinguished from enterococci because they are PYR (pyrrolidonyl arylamidase) negative, fail to hydrolyze arginine, and are typically unable to grow in 6.5 percent salt broth [2-4]. However, the traditional tests for enterococci (salt tolerance, growth on bile esculin agar, and expression of Lancefield group D antigen) may not allow a definitive distinction between enterococci and GDS, so either additional biochemical testing or molecular techniques are needed to avoid misidentification .
A study of 58 blood isolates of GDS identified to the subspecies level by 16S rRNA sequencing noted the following species breakdown :
●29 strains were S. gallolyticus subsp. gallolyticus (50 percent)