Clostridium Tetani

INTRODUCTION:
  • G+ve, noncapsulated
  • Culture - swarming growth
  • Spores are terminal, heat resistant and bulging giving a drumstick or tennis racket appearance
  • Produces 2 toxins - tetanolysin (hemolysin) and tetanospasmin(neurotoxin)
  • The main reservoir of cl. tetani is soil and intestine of animals and humans
  • The main mode of transmission is through trauma and contaminated wound
MORPHOLOGY :
  • Cl. tetani is Gram positive Bacillus,Non capsulated, Sporing, Obligatory anaerobe
  • Drum stick appearance; Spherical & terminal spores
  • The spores are spherical, terminal and bulging, giving the bacillus the characteristic 'drumstick' appearance. - Motile by peritrichate flagella except type IV which is non motile.
  • Tetanus spores are highly resistant to a number of injurious agents including boiling and autoclaving for 15 minutes at 120 ( Heat)
CULTURAL CHARACTERSTICS:
  • Shows swarming growth over the surface of agar. This property enables the sepration of Cl. tetani from mixed cultures. - `Filde's technique'.
  • Incubation period of clostridium tetani is 6-10 days
  • Grows well in Robertson's cooked meat broth.Shows Swarming growth on culture is characteristic of C.tetani
  • On blood agar, a-hemolysis is produced, which later develops into 13-hemolysis, due to the production of hemolysin (tetanolysin).
  • Tetanus spores are highly resistant to a number of injurious agents including boiling and autoclaving for 15 minutes at 120 ( Heat)
TOXIGENICITY
  • Tetanotysin (hemolysin) has no role in pathogenesis
  • Tetanospasmin block release of inhibitory neurotransmitters glycine and GABA of spinal cord, acting pre-synaptically → abolition of spinal inhibition → spread of uncontrolled impulses initiated elsewhere in the CNS
  • Filde's technique used to get pure cultures When the toxin is injected intramuscularly in one of the lower limbs - ascending tetanus is seen
  • When injected intravenously - descending tetanus seen
  • Strains of clostridium tetani are tested by production of toxins by following methods :
  • In vitro neutralization of toxin on blood agar
  1. The test is performed on blood agar containing 4% agar.
  2. High percentage of agar is used to inhibit swarming of C tetani.
  3. One half of medium is inoculated with tetanus antitoxin (1500 units/ml) while other half does not contain any antitoxin.
  4. Strains of clostridium are inoculated on both the halfs anaerobically for 8 hours.
  5. Colonies of clostridium shows hemolysis on part of agar without antitoxin.
  6. It is not a reliable test.
  • In vivo neutralization test on mice
  1. Two mouse are used.
  2. Control mouse is protected with 1000 unit of antitoxin one hour before the test.
  • 0.2 ml of 2-4 days old cooked meat culture of C tetani is incoulated in the tail of both the mouse.
  • Symptoms of ascending tetanus due to tetanospasmin produced by clostridium tetani develops in test mouse 12-24 hours after inoculation, no symptom occurs in control mouse.
Exam Question
  • The main reservoir of cl. tetani is soil and intestine of animals and humans
  • The main mode of transmission of cl. tetani is through trauma and contaminated wound
  • C.tetani is An anaerobic, gram-positive,spore forming, motile bacillus
  • Drumstick appearence is seen in cl. tetani
  • Swarming growth on culture is characteristic of C.tetani
  • Cl. tetani produce heat resisstant spores
  • Tetanospasmin is the Virulence factor for clostridium tetani
  • Tetanus is caused by clostridium tetani
  • Neonatal Tetanus is Caused by clostridium tetani
  • Incubation period of clostridium tetani is 6-10 days
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