by Seth Cowan. Tetanus is a disease caused by the bacteria Clostridium tetani, a gram negative rod bacterium. C. tetani spores generally reside in manure rich soils after being passed from the normal gut flora of animals.y Seth Cowan. Tetanus is a disease caused by the bacteria Clostridium tetani, a gram negative rod bacterium. C. tetani spores generally reside in manure rich soils after being passed from the normal gut flora of animals.