Clostridium tetani is a Gram-positive, motile bacterium found in soil and animal feces. Toxigenic strains of C. tetani contain a plasmid encoding the potent exotoxin which causes tetanus (lockjaw). The toxin is synthesized as a single 150 kDa protein chain which is cleaved ("nicked") into a 100 kDa heavy chain (fragment B) and a 50 kDa light chain (fragment A) connected by a disulfide bridge. Tetanus toxoid is produced by prolonged incubation of the toxin with formaldehyde and lysine, and is often used as a carrier for compounds of poor immunogenicity. This antibody binds to both tetanus toxin and tetanus toxoid.