Clinical manifestation and Pathogenesis of Streptococcus pyogenes

Virulence factors of Streptococcus pyogenes

A. Antigenic structure

  • M protein: rod like coiled structure with two major structural classes; Class I and Class II ;major virulence factor;resist phagocytosis and intracellular killing by polymorphonuclear leukocytes in the absence of antibodies.

B. Toxins and enzymes

  1. Streptokinase
  • It is also called as fibrinolysin.
  • It transforms the plasminogen of human plasma into plasmin, an active proteolytic enzyme that digests fibrin and other proteins, allowing the bacteria to escape from blood clots.
  1. Deoxyribonucleases
  • Streptococcal deoxyribonucleases A, B, C, and D degrades DNA (DNases) and similar to streptokinase facilitate the spread of streptococci in tissue by liquefying pus.
  1. Hyaluronidase
  • Hyaluronidase splits hyaluronic acid, an important component of the ground substance of connective tissue. Thus, hyaluronidase aids in spreading infecting microorganisms (spreading factor).
  1. Pyrogenic exotoxins (Erythrogenic toxins)
  • It act as superantigens, which stimulate T cells by binding to class II MHC complex and the activated T cell release cytokines that mediate shock and tissue injury.
  • It is associated with Streptococcal toxic shock syndrome and scarlet fever.
  1. Hemolysins
  • Two hemolysins are produced.
  • Streptolysin O which is oxygen labile and immunogenic in nature. It induces the production of Anti-Streptolysin O(ASO) after the infection with streptococci.
  • Streptolysin S which is oxygen stable and not immunogenic in nature. It s an agent responsible for the hemolytic zone around the streptococcal colonies on surface of blood agar.

Clinical manifestation and Pathogenesis of Streptococcus pyogenes

Clinical manifestation of Streptococcus pyogenes

Disease attributable to invasion by S pyogenes

1. Erysipelas

  • Portal of entry is skin
  • Raised lesion and red
  • Brawny edema

2. Cellulitis

  • Acute
  • Spreading infection of the skin and subcutaneous tissue
  • Pain, tenderness, swelling and erythema

3. Necrotizing fasciitis

  • Rapidly spreading necrosis of skin tissue and fascia

4. Puerperal fever

  • If the organism enter uterus after delivery, puerperal fever develops
  • Septicemia

5. Bacteremia and sepsis

  • Infection of traumatic or surgical wounds with streptococci results in bacteremia, which can rapidly be fatal

Disease attributable to local infection with S pyogenes and their byproduct

1. Streptococcal sore throat

  • Sub acute nasopharyngitis
  • Thin serous discharge
  • Fever
  • Infection extend to middle ear or mastoid
  • Enlarged cervical lymph nodes
  • Tonsillitis
  • Intense redness and edema of mucous membranes
  • Purulent exudates

2. Streptococcal pyoderma

  • Infection of superficial layer of skin : impetigo
  • Superficial vesicles
  • Denuded surface covered with pus and later encrusted

Invasive Group A Streptococcal infection

1. Streptococcal toxic shock syndrome and scarlet fever

  • Shock
  • Bacteremia
  • Respiratory failure
  • Multiorgan failure
  • Necrotizing fasciitis
  • Myositis
  • Fever
  • Erythema and desquamation

Poststreptococcal disease

1. Acute glomerulonephritis

  • Blood and protein in urine
  • Edema
  • High blood pressure
  • Urea nitrogen retention
  • Low serum complement levels
  • Chronic form leads to kidney failure

2. Rheumatic fever

  • Most serious sequela
  • Damage to heart muscles and valves
  • Fever
  • Malaise
  • A migratory non suppurative polyarthritis
  • Inflammation of all parts of heart ( endocardium, myocardium and pericardium)
  • Thickened and deformed valves

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