Streptococcus anginosus group

• S. anginosus
• S. constellatus
• S. intermedius

Gram Stain

• Gram positive cocci in tiny irregular clumps or chains (aerobic)

Clinical Significance

These organisms are part of the viridans group of streptococci and may be part of the commensal flora of the oropharynx, gastrointestinal tract, female urogenital tract, and upper respiratory tract. 

They are associated with deep and superficial abscesses (commonly with anaerobes), cervicofacial/dental infections, endocarditis, pulmonary infections (empyema/pleural effusions), central nervous system infections, bacteremia, endocarditis, osteomyelitis, septic arthritis, and rarely urinary tract infections.

There is emerging evidence in cystic fibrosis that S. anginosus group may work synergistically with Pseudomonas aeruginosa to cause disease.

S. anginosus - associated with polymicrobial infections (sinusitis, pleuropulmonary, intra-abdominal (including hepatobiliary), female urogenital and skin/soft tissue infections).

S. constellatus - associated with pleuropulmonary and intra-abdominal infections, often with anaerobes. It has been implicated in pharyngitis.

S. intermedius - most virulent and is associated with brain and hepatic abscesses, especially in children. Unlike S. anginosus and S. constellatus where co-isolation with anaerobes is typical, S. intermedius is often the sole organism isolated.

Usual Susceptibility Pattern

These organisms are typically susceptible to penicillin, amoxicillin, and ceftriaxone, although rare resistance does occur.

Susceptibility to clindamycin is variable.

Note: penicillin susceptibility does not necessarily predict susceptibility to ceftriaxone.