C. tetani is a slim, Gram-positive rod, which may stain Gram negative in very young or oldcultures. It forms spores readily in nature and in culture, yielding a typical round terminalspore that gives the organism a drumstick appearance before the residual vegetative celldisintegrates. The organism is flagellate and motile. C. tetani requires strict anaerobic con- ditions. Its identity is suggested by cultural and biochemical characteristics, but definite identification depends on demonstrating its neurotoxic exotoxin. C. tetani spores remainviable in soil or culture for many years. It is resistant to most disinfectants and withstandsboiling for several minutes.
The most important product of C. tetani is its neurotoxic exotoxin, tetanospasmin or tetanus toxin, a metalloproteinase that enzymatically degrades a protein required for docking of neurotransmitter vesicles at the appropriate site on presynaptic membranes. Loss of this function prevents release of neurotransmitters used by inhibitory afferent mo-tor neurons. The effect is unopposed firing of the motor neurons, generating spasms. The toxin is heat labile, antigenic, readily neutralized by antitoxin, and rapidly destroyed by intestinal proteases. Treatment with formaldehyde yields a nontoxic product or toxoid that retains the antigenicity of toxin and thus stimulates production of antitoxin.