Virulence factors and Clinical manifestation of Staphylococcus aureus

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Last Updated on June 28, 2020 by Sagar Aryal

Virulence factors of Staphylococcus aureus

A. Cell wall components

  1. Polysaccharide Capsule: inhibits phagocytosis
  2. Peptidoglycan: activates complement, IL-1, chemotactic to PMNs
  3. Teichoic acid: species specific, mediate binding to fibronectin
  4. Protein A: It binds to the Fc region of IgG and complement ,exerting an anti-opsonin effect.
  5. Fibronectin binding protein(FnBP): promote binding to ,mucosal cells and tissue matrices.
  6. Clumping factor: FnBP enhances clumping of organism in presence of plasma.

B. Enzymes

  1. Catalase enzyme: conversion of hydrogen peroxide into water and oxygen
  2. Coagulase enzyme and clumping factor: an enzyme like protein that clots oxalated or citrated plasma.
  3. Other enzymes: hyaluronidase(spreading factor), staphylokinase(fibrinolysis), protienases, lipases, β- lactamases

C. Toxins

  1. Exotoxins: comprises of four toxins α,β,γ,δ: also called hemolysin,
    – α exotoxins- heterogenous protein acts on broad spectrum of eukaryotic cell membranes
    – β exotoxins- degardes sphingomyelin
    – δ exotoxins- disrupts biological membrane
    – γ exotoxins- interact with two proteins to form six potential two component toxins. All six toxins lyse WBC by pore formation in the cellular membranes that increase cation permeability
  2. Panton Valentine leukocidin: composed of two components S and F whichact synergistically to kill white blood cells
  3. Exfoliative toxins: composed of type A- located on phage and headt stable and type B- plasmid mediated and heat labile: yield generalized desquamation scalded skin syndrome
  4. Toxic shock syndrome toxins (TSST-1): prototypical superantigen which bind with MHC-II yielding T-cell stimulation. Toxic is associated with fever, shock and multisystem involvement.
  5. Enterotoxins: altogether 15 enterotoxins(A-E,G-P), heat stable, resistant to gut enzymes

Virulence factors and Clinical manifestation of Staphylococcus aureus

Clinical manifestation of Staphylococcus aureus

A. Localized skin infections

  1. Infections are small superficial abscesses involving hair follicle, sweat or sebaceous glands.
  2. Subcutaneous abscesses called furuncles (boils) often formed around foreign bodies
  3. Carbuncles are larger, deeper, multiloculated skin infections that can lead to bacteremia
  4. Impetigo is usually localized, superficial, spreading crusty skin lesions

B. Deep localized infections

  1. Metastatic from superficial infections or skin carriage or may result from trauma.
  2. Acute infection of joint space in children.

C. Acute endocarditis

  1. Generally associated with intravenous drug users.
  2. Bacteria can be introduced into soft tissue and the bloodstream.

D. Septicemia

  1. Generalized infection with sepsis or bacteremia associated with a known focus or not

E. Pneumonia

F. Nosocomial infections

  1. hospital associated infections often of wounds or bacteremia associated with catheter.

G. Toxin mediated infections

  • Toxic shock syndrome

  • High Fever
  • Rash
  • Vomiting
  • Diarrhea
  • Hypotension
  • Multiorgan involvement
  • Staphylococcal gastroenteritis

  • Nausea
  • Vomiting
  • Diarrhea
  • Scalded skin syndrome

  • Appearance of superficial bullae
  • Marked epithelial desquamation

Virulence factors and Clinical manifestation of Staphylococcus aureus

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