Staphylococcus aureus: Virulence and Toxin

VIRULENCE FACTOR:

TOXINS Cytolytic Toxins

α-Hemolysin	Protein inactive at 70oC Reactivated paradoxically at 100″C. Less active against human erythrocytes. Leukocidal Cytotoxic Dermonecrotic Neutotoxic Lethal.
β- Hemolysin	Hot cold phenomenon Sphingomyelinase Hemolytic for sheep cells.
δ  – Hemolysin	Detergent like effect on cell membranes, Plays role in S. aureus diarrhea disease
γ – Hemolysin	Bicomponent protein.
Leukocidin (Panton valentine Toxin	Bi component toxin Associated with farunculosis Important virulence factor in MRSA infection. Kills WBCS by producing holes in their CM

Enterotoxin

• Act on ANS to cause illness
• Preformed
• Types:A, B, C 1-3, D, E and H
• Heat stable toxin
• Responsible for staphylococcal food poisoning which occur 2-5 hrs after consuming meat and fish or milk products.

Source:

• Usually food handler which is carrier.
• Mechnism: Type A toxin is responsible for most cases.
  • Toxin acts directly on autonomic nervous system (Vagal stimulation) andvomiting center.

TSST

• Produce fever, skin rashes,diarrhoea,conjunctivitis,and death to shock
• TSST-1 = Enterotoxin F = Pyrogenic Exotoxin C is responsible for most cases.
• TSST-1 binds to MHC class II molecules, yieldingT-Cell stimulation.
• Staph. Enterotoxin and TSST are super antigen 
• Leading to an excessive and non regulated immune response.

Exfoliating toxin/Epidermotolytic Toxin / ET / Exfoliatin

• Breaks intracellular bridges in the stratum granulosum of epidermis
• Causes its separation from underlying tissue
• Resulting in a blistering and exfoliating disease of skin
• Cause staphylococcal scalded skin syndrome (SSS).
• Severe form is called Rittels disease in neonate arrd toxic epidermal neuolysis in elderly.
• Milder form are pemphigus neonatorum and bullous impetigo.

Two type:

• ETA (chromosomal gene product, heat stable)
• ETB (plasmidnmediated, heat labile). 
• Possess serine protease activity which triggers exfoliation.

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