Clostridium tetani is a bacterium that causes tetanus in humans. Clostridium tetani are Gram-positive, spore-forming rods that are anaerobic. If they enter the body through a wound, they can multiply and produce a toxin that affects the nerves and controls the activity of muscles. Toxin of Clostridium tetani binds to membranes of peripheric nervous cells and inhibits the release of neurotransmitters.