Tetanus is a disease caused by the toxin produced by an anaerobic bacterium: Clostridium tetani. That this disease still occurs is tragic in view of the fact that it can be completely prevented by vaccination. The disease cannot be transmitted from human-to-human. Clostridium tetani is a strictly anaerobic Gram-positive rod-shaped bacterium. In cultures or in tissue it can be Gram-variable. It forms a characteristic spore at one end (exclamation mark, tennis racket). These spores are very resistant: they resist boiling, short autoclaving, alcohol and phenol. They are destroyed by autoclaving at 121°C for at least 12 minutes (better 15'). The bacterium occurs widely in nature, for example in the soil and in the intestinal tract (especially of cattle and horses). Approximately 10% of people have C. tetani in their colon.