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Tufts OpenCourseware
Author: Amelia Virostko

1. Identification of Streptococci

  1. Gram-positive cocci
  2. Hemolysis on blood agar plates
    1. α green color due to partial lysis
    2. β clear color due to complete lysis
    3. γ no hemolysis
  3. Lancefield group based on cell-wall carbohydrate antigen
  4. Species according to metabolic reactions

2. S. pyogenes (Group A Strep or GAS)

  1. β-hemolytic
  2. Syndromes caused by GAS
    1. Pharyngitis: mild infection of the throat
    2. Impetigo: superficial skin infection that causes honey-brown crusts
    3. Erysipelas: serious and deeper skin or soft tissue infection
    4. Necrotizing Fasciitis: severe fascial and tissue infection with high morbidity and mortality rates
    5. Scarlet Fever: caused by erythrogenic toxin that leads to sore throat, fever, and rash
    6. Toxic Shock: high fever and shock
    7. Acute Rheumatic Fever: occurs after untreated pharyngitis and causes myocarditis, arthritis, chorea, and rash
    8. Acute Glomerulonephritis: antigen-antibody complex deposited in kidneys causing edema, hypertension, and rust-colored urine
  3. Spread
    1. Possible spread depending on syndrome
  4. Virulence Factors
    1. M protein: anti-phagocytic and anti-complement
    2. Erythogenic toxin: causes rash in scarlet fever
    3. Exotoxin A: pyrogenic superantigen
    4. Hyaluronidase: degrades hyaluronic acid
    5. Streptokinase: activates plasmin
    6. Nucleases
    7. Streptolysin O and Streptolysin S: lyse red and white blood cells
    8. Protein F and Lipotechoic acid: bacterial attachment
    9. Protein G: binds IgG
    10. Hyaluronic capsule: anti-phagocytic
    11. C5a peptidase: inactivates C5a
  5. Damage
    1. Local, tissue damage, sepsis, or organ failure depending on syndrome
  6. Treatment
    1. Penicillin
      1. Must treat pharyngitis for 10 days to prevent acute rheumatic fever

3. S. pneumoniae

  1. Leading cause of bacterial pneumonia
    1. Risk factors: cigarette smoking, alcohol consumption, excess fluid in lungs, splenectomy (capsulated), pre-existing lung infection, immunocomprised
  2. Can also cause otitis media, meningitis (capsule), sinusitis, and bronchitis
  3. Identification
    1. Often found as diplococci
    2. Optochin-sensitive
    3. α-hemolytic and catalase negative
  4. Encounter/Entry
    1. Found in nares and throat of humans
    2. Inhalation of respiratory droplets
  5. Virulence Factors
    1. Polysaccharide capsule: anti-phagocytic
    2. Choline binding protein A: binds glycoproteins on host cells
    3. Neuraminidase: exposes receptors on host cells
    4. IgA protease: inactivates IgA
    5. Autolysin
    6. Pneumolysin
  6. Treatment
    1. Vancomycin or 3rd generation cephalosporins
    2. 30% of strains are now penicillin-resistant