Clostridium tetani

Clostridium tetani

Organism

Clostridium tetani is a moderately-sized gram-positive, endospore-producing bacillus.
Motile with a peritrichous (def) arrangement of flagella.
Produce round, terminal endospores that give the bacterium a "tennis-racquet" appearance.
An obligate anaerobe(def).

Habitat

Colonizes the intestinal tract in humans and animals.

Source

Endospores found in fertile soil or feces.

Epidemiology

Endospores are found in most soils and in the intestinal tract of many animals and humans.
Although exposure to endospores is commom, disease is uncommon except in countries with poor medical care and vaccination compliance.
Fewer than 50 cases per year in the U.S.; most in elderly individuals with waning immunity.
It is estimated that there is more than one million cases a year worldwide, with a mortality rate of 20% to 50%.
Most deaths occur in neonates and originates from infection of umbilical stumps in mothers that have no immunity.

Clinical Disease

Generalized tetanus is most common. Typical presenting symptoms include lockjaw and sardonic smile, arrising as a result of spastic paralysis (def) of the masseter muscles (def) and other facial muscles. Difficulty in swallowing, drooling, irritability, and persistent back spasms are other early symptoms. When the autonomic nervous system is involved, symptoms include perfuse sweating, hyperthermia (def), cardiac arrhythmias (def), and fluctuations in blood pressure.
Cephalic infection primarily infects the head and involves cranial nerves.
Localized infection involves the muscles in the area of primary injury.
Neonatal tetanus is in newborns and originates from infection of umbilical stumps in mothers that have no immunity.
The infection begins when endospores of C. tetani enter an anaerobic wound (def). Since the bacterium is an obligate anaerobe, an anaerobic environment is needed for the endospores to germinate and the vegetative bacteria to grow. Vegetative bacteria eventually produce tetanospasmin, the toxin responsible for symptoms of tetanus.

Pathogenicity

Produces an A-B (Type III) (def) toxin called tetanospasmin. This is a neurotoxin that binds to inhibitory interneurons of the spinal cord and blocks their release of inhibitor molecules. It is these inhibitor molecules from the inhibitory interneurons that eventually allow contracted muscles to relax by stopping excitatory neurons from releasing the acetylcholine that is responsible for muscle contraction. The toxin, by blocking the release of inhibitors, keeps the involved muscles in a state of contraction and leads to spastic paralysis (def), a condition where opposing flexor and extensor muscles simultaneously contract. Death is usually from respiratory failure.
Endospores enable the bacterium to survive indefinitely in soils and other environments.

Treatment

Treatment involves debridement, the antibiotic metronidazole* (see antibiotic table), active immunization (def) with tetanus toxoid (def), and passive immunization (def) with tetanus immune globulin (def).
Prevention is through active immunization with tetanus toxoid**. The toxoid stimulates the body to make neutralizing antibodies against the binding component of the tetanus toxin. Once the antibody binds to the toxin, the toxin can no longer bind to the receptors on the host cell membrane.

*Drugs may change with time.

** CDC Recommendations for tetanus prophylaxis.

For a more detailed article on tetanus, see Tetanus, by Daniel J Dire, MD, FACEP, FAAEM, Associate Professor, Department of Emergency Medicine, University of Alabama at Birmingham and Daniel J Dire, MD, FACEP, FAAEM, is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, Association of Military Surgeons of the US, and Society for Academic Emergency Medicine