Streptococcus

Characteristics

Streptococcus pyogenes (Group A)

• β-hemolytic (complete hemolysis).
• Bacitracin-sensitive.
• PYR-positive.
• ASO/Anti-DNase B titers for post-infectious sequelae.

Streptococcus agalactiae (Group B)

• β-hemolytic.
• Bacitracin-resistant.
• CAMP test-positive (arrowhead hemolysis).
• Hippurate hydrolysis-positive.

Streptococcus pneumoniae

• α-hemolytic (partial, green hemolysis).
• Lancet-shaped diplococci.
• Optochin-sensitive.
• Bile-soluble.
• Urine antigen test can be used for pneumonia.

Viridans Group Streptococci

• α-hemolytic.
• Optochin-resistant.
• Bile-insoluble.

Streptococcus gallolyticus (S. bovis)

• Grows in bile.
• Does NOT grow in 6.5% NaCl.
• PYR-negative.
• Finding in blood warrants a colonoscopy.

Enterococcus

• Grows in bile.
• Grows in 6.5% NaCl.
• PYR-positive.

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Diseases

Alpha-hemolysis (partial hemolysis)

• Streptococcus pneumoniae (pneumococcus)

  • Otitis media (especially in children)
  • Sinusitis, pharyngitis
  • Pneumonia (rusty-colored sputum)
  • Meningitis
  • OPSI (in individuals with asplenia or sickle cell disease)

• Viridans streptococci (e.g., S. mutans, S. mitis, and S. sanguinis)

  • Dental caries (S. mutans and S. mitis)
  • Subacute bacterial endocarditis (S. sanguinis)

Beta-hemolysis (complete hemolysis)

• Streptococcus pyogenes (Group A Streptococcus)

  • Head and neck:
    • Pharyngitis
    • Tonsillitis
    • Peritonsillar abscess
    • Otitis media
  • Skin and soft tissues (pyogenic):
    • Erysipelas
    • Cellulitis
    • Impetigo (“honey-crusted” lesions)
    • Necrotizing fasciitis
  • Toxin-mediated disease:
    • Scarlet fever
    • Streptococcal toxic shock-like syndrome
  • Immunologic complications (after primary infection):
    • Acute rheumatic fever
    • Poststreptococcal glomerulonephritis

• Streptococcus agalactiae (Group B Streptococcus, GBS)

  • Adults (often asymptomatic, but can cause):
    • Urinary tract infection
    • Meningitis
    • Pneumonia
    • Soft tissue infection
  • Newborns:
    • Neonatal meningitis and pneumonia
    • Neonatal sepsis
    • Early-onset group B streptococcal infection
    • Late-onset group B streptococcal infection

• Streptococcus gallolyticus

  • Bacteremia
  • Endocarditis
  • Colorectal carcinoma

• Streptococcus anginosus

  • Soft tissue infections (e.g., cellulitis, necrotizing fasciitis)
  • Abscesses (e.g., brain abscess, abdominal abscess)
  • Septicemia