Clostridium tetani

Clostridium tetani is a gram positive bacilli that causes tetanus. This organism exists as a gut commensal as well as in the soil. The organism remains localized at the portal of entry, but produces an exotoxin (tetanospasmin) which acts on the CNS. Also, it produces an oxygen-labile haemolysin of unknown pathogenicity.

C. tetani bears spherical spores in its terminal regions which are resistant to drying and antiseptics. The spores are also partly resistant to heat. Morphologically, the appearance of bacilli with spores has been likened to a 'drumstick'.

C. tetani is a strict anaerobe. It can grow on ordinary media at 37 degrees centigrade to produce a spreading, thin growth that is often poorly visible.

Tetanospasmin reaches the central nervous system by intraaxonal transport, moving at a rate of 75 to 250 nm per day (1).

• this toxin produces presynaptic blockade of the synapses on inhibitory Renshaw cells and Ia fibres of alpha motor neurons that handle the transmission of gamma - aminobutyric and glycine, but not of the Renshaw cells that handle acetylcholine transmission
• tetanospasmin binding appears to be irreversible
• recovery of function depends on the sprouting of new axonal terminals

Reference:

• Sanford JP (1995). Tetanus - forgotten but not gone. NEJM, 332, 812-3.