Streptococcus anginosus (S. anginosus)

Streptococcus anginosus is a Gram-positive, catalase-negative bacterium that belongs to the Streptococcus anginosus group (SAG), historically known as the Streptococcus milleri group (StatPearls). It is a common commensal of the human oral cavity, gastrointestinal tract, and genitourinary tract, but it is also a significant opportunistic pathogen (NCBI). S. anginosus is uniquely characterized by its strong association with pyogenic infections and the formation of abscesses in various organs, including the brain, liver, and lungs (PubMed). The organism produces several virulence factors, such as intermedilysin and various hydrolytic enzymes, which facilitate tissue invasion and the development of pus (Journal of Clinical Microbiology). In clinical settings, it is often identified by its characteristic caramel-like odor on agar and its variable expression of Lancefield group antigens A, C, F, or G (StatPearls). Treatment typically involves beta-lactam antibiotics like penicillin or ceftriaxone, although surgical drainage of abscesses is frequently required for clinical resolution (NIH). While generally susceptible to penicillins, some strains have shown increasing resistance to macrolides and tetracyclines, necessitating careful susceptibility monitoring (CDC). Its ability to thrive in acidic environments and form biofilms further enhances its pathogenicity in deep-tissue infections (Microbiology Society).

Other names

Streptococcus milleri groupSAGStreptococcus anginosus group

Antibiotics targeting this organism primarily act by inhibiting bacterial cell wall synthesis through the binding of penicillin-binding proteins (beta-lactams and glycopeptides) or by inhibiting protein synthesis via the 50S ribosomal subunit (lincosamides).