24.3 CASE STUDY

Compare the mode of action of the toxins produced by C. tetani and C. botulinum.

Exactly, the key difference between the two toxins lies in their modes of action and the resulting clinical presentations:

Tetanospasmin (produced by C. tetani):

• Causes spastic paralysis.

• It blocks the release of inhibitory neurotransmitters, specifically glycine and gamma-aminobutyric acid (GABA). This results in constant stimulation of the muscles, leading to the characteristic spasms and rigidity seen in tetanus.

Botulinum toxin (produced by C. botulinum):

• Causes flaccid paralysis.

• It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction. This leads to muscle paralysis, as muscles cannot contract without acetylcholine signaling.

While both toxins target neurotransmitter release, the key distinction is that tetanospasmin increases muscle contractions by inhibiting inhibitory signals, while botulinum toxin directly stops the excitatory signal, leading to muscle relaxation and paralysis.

Mind Map: Compare the mode of action of the toxins produced by C. tetani and C. botulinum

Tetanospasmin (produced by C. tetani):

• Causes spastic paralysis.

• Blocks the release of inhibitory neurotransmitters:

  • Glycine

  • Gamma-aminobutyric acid (GABA)

• Results in constant muscle stimulation:

  • Characteristic spasms

  • Rigidity seen in tetanus

Botulinum toxin (produced by C. botulinum):

• Causes flaccid paralysis.

• Prevents the release of acetylcholine:

  • Neurotransmitter at the neuromuscular junction

• Leads to muscle paralysis:

  • Muscles cannot contract without acetylcholine signaling

Key distinction:

• Tetanospasmin:

  • Increases muscle contractions by inhibiting inhibitory signals

• Botulinum toxin:

  • Directly stops the excitatory signal

  • Leads to muscle relaxation and paralysis