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"Streptococcus milleri" endocarditis caused by Streptococcus anginosus

Patrick C Y Woo1, Herman Tse, Kai-ming Chan

  • 1Department of Microbiology, The University of Hong Kong, Hong Kong.

Diagnostic Microbiology and Infectious Disease
|February 20, 2004
PubMed

Insights

Members of the Streptococcus milleri group, particularly Streptococcus anginosus, can cause infective endocarditis. Accurate species identification is crucial for diagnosing and treating this serious heart infection, especially in cases of bacteremia.

Area of Science:

  • Infectious Diseases
  • Microbiology
  • Cardiology

Background:

  • The Streptococcus milleri group, unlike other viridans streptococci, is known for abscess formation but rarely causes infective endocarditis.
  • Previous studies indicated varying associations with abscesses among S. intermedius, S. constellatus, and S. anginosus, but their role in infective endocarditis remained unclear.

Purpose of the Study:

  • To investigate the relative importance of the three species within the Streptococcus milleri group as causes of infective endocarditis.
  • To evaluate the diagnostic accuracy of conventional methods versus 16S ribosomal RNA (rRNA) gene sequencing for identifying these bacteria in endocarditis cases.

Main Methods:

  • A retrospective analysis of 6 infective endocarditis cases caused by the Streptococcus milleri group over a 5-year period.
  • Identification of isolates using 16S ribosomal RNA (rRNA) gene sequencing, Vitek (GPI), and API (20 STREP) systems.
  • Review of patient demographics, underlying conditions, bacteremia characteristics, and treatment outcomes.

Main Results:

  • All 6 identified cases of Streptococcus milleri group endocarditis were caused by Streptococcus anginosus, confirmed by 16S rRNA gene sequencing.
  • Conventional identification systems (Vitek and API) failed to accurately identify the isolates to the species level with high confidence.
  • Patients often had predisposing factors such as chronic rheumatic heart disease or intravenous drug abuse; mortality was observed in 2 cases.

Conclusions:

  • Streptococcus anginosus is a significant, albeit rare, cause of infective endocarditis within the Streptococcus milleri group.
  • 16S rRNA gene sequencing is superior to conventional methods for accurate species identification, which is critical for guiding clinical management.
  • Infective endocarditis should be suspected and investigated in patients with monomicrobial S. anginosus bacteremia, particularly when detected in multiple blood cultures.

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