Which organism is primarily responsible for tetanus?

• A. Escherichia coli
• B. Clostridium tetani
• C. Bacillus subtilis
• D. Bacillus cereus

Answer: (B)

Tetanus is caused by a toxin-producing bacterium that thrives in low-oxygen environments, especially in deep wounds. The organism primarily responsible is Clostridium tetani, a spore-forming anaerobe found in soil and animal feces. It releases tetanospasmin, a neurotoxin that travels to the nervous system and blocks the release of inhibitory neurotransmitters GABA and glycine, leading to unrestrained motor neuron activity and the severe muscle stiffness and spasms seen in tetanus (often starting with lockjaw).

Escherichia coli is a common gut bacterium and not linked to tetanus; Bacillus subtilis is typically nonpathogenic and used in labs; Bacillus cereus can cause food poisoning but does not produce tetanospasmin.