Clostridium tetani

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Kingdom: Bacteria ; Division: Firmicutes; Class: Clostridia; Order: Clostridiales; Family: Clostridiaceae; Genus: Clostridium; Species: C. tetani

Binomial name Clostridium tetaniFlügge, 1886

Clostridium tetani is a rod-shaped, anaerobic bacterium of the genus Clostridium. Like other Clostridium species, it is Gram-positive, and its appearance on a gram stain resembles tennis rackets or drumsticks. C. tetani is found as spores in soil or as parasites in the gastrointestinal tract of animals. C. tetani produces a potent biological toxin, tetanospasmin, and is the causative agent of tetanus.

Tetanus was well known to ancient peoples, who recognized the relationship between wounds and fatal muscle spasms. In 1884, Arthur Nicolaier isolated the strychnine-like toxin of tetanus from free-living, anaerobic soil bacteria. The etiology of the disease was further elucidated in 1884 by Antonio Carle and Giorgio Rattone, who demonstrated the transmissibility of tetanus for the first time. They produced tetanus in rabbits by injecting their sciatic nerve with pus from a fatal human tetanus case in that same year. In 1889, C. tetani was isolated from a human victim, by Kitasato Shibasaburo, who later showed that the organism could produce disease when injected into animals, and that the toxin could be neutralized by specific antibodies. In 1897, Edmond Nocard showed that tetanus antitoxin induced passive immunity in humans, and could be used for prophylaxis and treatment. Tetanus toxoid vaccine was developed by P. Descombey in 1924, and was widely used to prevent tetanus induced by battle wounds during World War II.

Characteristics
C. tetani is a rod-shaped, obligate anaerobe which stains Gram positive in fresh cultures; established cultures may stain Gram negative. During vegetative growth, the organism cannot survive in the presence of oxygen, is sensitive to heat and has flagella which provide limited mobility. As the bacterium matures, it develops a terminal spore, which gives the organism its characteristic appearance. C. tetani spores are extremely hardy, and are resistant to heat and most antiseptics. The spores are distributed widely in manure-treated soils, and can also be found on human skin and in contaminated heroin.

Treatment
When a tetanus infection becomes established, treatment usually focuses on controlling muscle spasms, stopping toxin production, and neutralizing the effects of the toxin. Treatment includes administration of tetanus immune globulin (TIG), which comprises antibodies that inhibit tetanus toxin (also known as tetanus antitoxins), by binding to and removing unbound tetanus toxin from the body. Binding of the toxin to the nerve endings appears to be an irreversible event, and TIG is ineffective at removing bound toxin. Recovery of affected nerves requires the sprouting of a new axon terminal. Large doses of antibiotic drugs (such as metronidazole or intramuscular penicillin G) are also given once tetanus infection is suspected, to halt toxin production.

Prevention of tetanus includes vaccination, and cleaning the primary wound. Prophylaxis is effective, in the form of a tetanus toxoid vaccine, which is given with or without passive immunization with tetanus immune globulin. Very few cases of tetanus have occurred in individuals with up-to-date tetanus vaccinations. DPT vaccine (diphtheria-pertussis-tetanus) in North America, is given at 2, 4, 6, and 15–18 months of age, followed by a booster before entry to school (4-6 years). This regimen provides protection from tetanus for about 10 years, and every 10 years thereafter, a booster shot of tetanus vaccine is recommended.Tetanus is not contagious from person to person, and is the only vaccine-preventable disease that is infectious but not contagious. A C. tetani infection does not result in tetanus immunity, and tetanus vaccination should be given as soon as the patient has stabilized.