Tetanus is caused by infection with which organism?

• A. Clostridium botulinum
• B. Clostridium tetani
• C. Streptococcus suis
• D. Bacillus anthracis

Answer: (B)

Clostridium tetani is the organism that causes tetanus. It’s a strict anaerobe that forms spores and is commonly found in soil. In a wound with limited oxygen, these spores germinate and release tetanospasmin, a powerful neurotoxin. The toxin travels along nerves to the spinal cord and brain, where it blocks the release of inhibitory neurotransmitters like GABA and glycine. Without these brakes, motor neurons fire too strongly, leading to the characteristic muscle rigidity and spasms, often starting with lockjaw.

The other organisms listed cause different diseases. Clostridium botulinum produces botulinum toxin, which blocks acetylcholine release at the neuromuscular junction and causes flaccid paralysis. Streptococcus suis is a pig-associated bacterium that can cause meningitis and other infections in animals and people but not tetanus. Bacillus anthracis causes anthrax through its own toxins, not tetanospasmin. Therefore, the organism responsible for tetanus is Clostridium tetani.