Which statement is true of Clostridium tetani?

• A. It produces rapid tissue necrosis
• B. It is a gram-positive, nonspore-forming bacillus
• C. Microorganisms commonly found in the microbiome of the intestinal tract
• D. Disease is caused by an exotoxin acting on the central nervous system

Answer: (D)

Tetanus is driven by a secreted exotoxin that targets the nervous system. The toxin, tetanospasmin, is produced by Clostridium tetani in an anaerobic wound and travels to the central nervous system, where it blocks the release of inhibitory neurotransmitters like GABA and glycine. This loss of inhibition causes motor neurons to fire inappropriately, leading to the characteristic muscle rigidity and spasms of tetanus. This toxin-mediated CNS effect is why the statement is true.

The other ideas don’t fit tetanus: rapid tissue necrosis is more typical of other clostridial infections, and Clostridium tetani is actually a gram-positive, spore-forming bacillus (not nonspore-forming). It is not a common resident of the intestinal microbiota. Vaccination with tetanus toxoid works by neutralizing this toxin, preventing disease.