Streptococcus anginosus group

Background

Microbiology

• Catalase negative, variably hemolytic Gram-positive cocci within the viridans group streptococci
• Contains Streptococcus anginosus, Streptococcus constellatus, and Streptococcus intermedius
  • S. anginosus has two subspecies: S. anginosus subsp. anginosus and S. anginosus subsp. whileyi
  • S. constellatus has three subspecies: S. constellatus subsp. constellatus, S. constellatus subsp. pharyngis, and S. constellatus subsp. viborgensis
• Have a buttered popcorn smell on plate
• Normal flora of oral cavity, throat, stool, and vagina
• Identified using three rapid tests:
  • Voges-Proskaur (VP) test for acetoin production
  • Arginine hydrolysis
  • Failure to ferment sorbitol

Clinical Manifestations

• Tendency to form abscesses, unlike other streptococci, which can be polymicrobial with anaerobes and Enterobacterales
• Infections can range in severity, and include pharyngitis, dental abscess, skin and soft tissue infection, pneumonia, empyema, lung abscess, brain abscess, liver abscess, and kidney abscess

Investigations

• Presence of bacteremia without focus should prompt investigations to identify an occult abscess
• The HANDOC score can assess need for echocardiography

Management

• Typically treated with ceftriaxone or other third-generation cephalosporin pending susceptibilities
• If found in an abscess, should be considered polymicrobial and treated with concomitant metronidazole
• Clindamycin resistance is high, approximately 20-30%