Clostridium tetani is an anaerobic pathogenic bacterium that is primarily found in soil and animal intestinal tracts. As characteristic of all bacteria, C. tetani bacteria are single-celled and do not contain any membrane-bound organelles, such as a nucleus. This bacterium is Gram-positive, meaning it lacks an outer lipopolysaccharide membrane and possesses only a thick peptidoglycan cellular wall. However, established vegetative bacterium occasionally stain Gram-negative, indicating a development of a thin lipopolysaccharide membrane. This bacterium is characteristically rod-shaped and flagellated in its vegetative state, and drumstick shaped in its spore form. There are currently eleven identified strains of C. tetani, and all eleven strains are known to produce an identical neurotoxin known as tetanospasmin. This potent toxin is the cause of the central nervous condition known as tetanus, which is commonly fatal unless treated.
Figure 1 is an unrooted phylogram detailing the phylogeny of the Clostridium genus relative to other bacterial genera. Clostridium has been highlighted by a white border for ease of location.