VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

TOXINS

• C.tetani produces atleast two distinct toxins.
  • Tetanospasmin
  • Tetanolysin
• They are antigenically and pharmacologically distinct and their production is mutually independent.
• A third toxin – a nonspasmogenic peripherally active neurotoxin has been identified recently.
• It is not known whether this plays any role in the pathogenesis of tetanus.

Tetanolysin

• It is a heamolysin or cytotoxin causing lysis of rabbit and horse RBC’S.
• It is heat and oxygen labile, similar to those of streptolysin O, d toxin. (C. oedematiens) and j toxin (C. welchii).

Tetanospamin

• It is a very potent neurotoxin responsible for the clinical manifestations of tetanus.
• It is oxygen stable, but relatively heat labile, being inactivated at 65⁰C in 5mts.
• The highly purified form gets toxoided spontaneously.
• It is a good antigen and is specifically neutralized by the antitoxin. The toxin exists in two forms.
• A monomer of MW 68000, which is toxic and a dimer is which is non toxic but antigenic.
• The purified toxin is active in extremely small amounts and it contains about 3x10⁷ minimum mouse lethal dose per mg protein.
• There is considerable variation in the susceptibility of different species of animals to the toxin.
• The horses and human are the most susceptible.
• Guinea pigs, mice, goats and rabbits are susceptible in that descending order. Birds and reptiles are highly resistant.