Clostridium tetani

It is the causative agent of the potentially fatal condition tetanus.

Morphology

It is an obligate anaerobe, gram positive, rod shaped bacillus shaped like a drumstick or tennis racket, endospore forming and motile with rotary peritrichous flagella.

Classification

Not relevant.

Human Pathology

Disease is caused by the spores entering the body through cuts in the skin or from the use of non sterile instruments contaminated with spores to cut the umbilical cord during birth causing neonatal tetanus. 'Skin popping” by drug addicts can also cause tetanus due to exposure to spores. Toxins tetanospasmin and tetanolysin play a key role in pathogenesis and disease manifestations.

Tetanospasmin is transported in a retrograde fashion from the neuromuscular junction to the spinal cord where it inhibits the release of inhibitory neurotransmitters GABA and glycine causing hyperactivity of the lower motor neurons, which manifests as muscle rigidity and spasms. Tetanolysin acts as a tissue lysin and breaks down tissues.

Tetanus can be neonatal (in newborns), cephalic (localized to head region), local or generalized. It presents as a stiff neck, opisthotonus (backward arching of the head, neck , spine due to extreme spasm), trismus or lockjaw, “risus sardonicus” which looks like a grin due to sustained spasm of facial muscles and generalized rigidity causing apnoea, dysphagia eventually causing death.

Laboratory diagnosis of tetanus

Clinical evaluation is key for diagnosis. Organisms are rarely isolated from the wound site. On gram stain they show typical morphology with terminal endospores. If culture is done it must be anaerobic only.