Clostridia are spore-forming, Gram-positive, anaerobes (although some species are microaerophilic). They are known to produce a variety of toxins, some of which are fatal.The genomes of both Clostridium tetani, the etiological agent of tetanus, and Clostridium perfringens, the etiological agent of gas gangrene have been sequenced. The genome of C. tetani is 2,799,250 bp long with 2,372 open reading frames. C. tetani also contains a plasmid that measures 74,082 bp long with 61 open reading frames and encodes the tetanus toxin.The genome of Clostridium perfringens is 3,031,430 bp long with 2,660 open reading frames and a low G+C content of 28.6%. C. perfringens is an excellent model for genetic studies of the clostridium genus due to its oxygen tolerance and fast growth rate. The genome contains, as would be expected, the typical anaerobic fermentation enzymes leading to gas production (one of the characteristics of gas gangrene, the disease it causes), but no enzymes for the tricarboxylic acid cycle of respiratory chain.Clostridia are commonly found in the environment. They inhabit soil, sewage, and marine sediments, as well as the intestines of both animals and humans. Several species of clostridia are used industrially for the production of alcohols and commercial solvents. A few species, such as C. butyricum and C. pasteurianum fix nitrogen. The spores of clostridia are produced during times of stress, and can persist in toxic environments where the anaerobic bacteria cannot.There are three species of clostridia that cause widely recognized and often-deadly diseases. Clostridium tetani is the etiological agent of tetanus, Clostridium botulinum is the etiological agent of botulism, and Clostridium perfringens is one of the etiological agent of gas gangrene. Tetanus is contracted through contact between spores of C. tetani and an open wound, such as stepping on a rusty nail. If an anaerobic environment is present the spores will germinate. Tetanus is a neurological disease. C. tetani releases an exotoxin called tetanus toxin, which blocks the release of neurotransmitters from the presynaptic membrane of inhibitory interneurons of spinal cord and brainstem of mammals that regulate muscle contraction. This leads to continuous muscle contraction primarily in the neck and jaw muscles (lockjaw). If the infection is left untreated, it will eventually lead to respiratory failure and death. If not treated early, mortality rates for tetanus are relatively high. After World War II with the introduction of the tetanus vaccine, C. tetani infection has become relatively rare in industrialized countries, and almost all cases are due to insufficient immunization.Clostridium botulinum causes botulism, which is contracted through contact (usually ingestion) of botulinum toxin (wound botulism is rare, but can occur). There are about 10-30 outbreaks of botulism reported annually in the United States, almost all of which are associated with improperly canned or processed food (usually home-canned). Sausages, meat products, canned vegetables, and seafood are the most frequent vehicles of C. botulinum. Because clostridium spores can be airborne, they often find their way onto food that is going to be canned, which provides a pleasant anaerobic environment for the spores to germinate and release their toxin. Botulinum toxin is a protein that C. botulinum secretes, which causes muscle paralysis by blocking the presynaptic release of the neurotransmitter acetylcholine. The onset of symptoms for foodborne botulism is usually 18-36 hours after the ingestion of infected food. The toxin causes paralysis that progresses symmetrically downward, usually starting with the eyes and face, then down to the throat, chest, and extremities. Once the chest muscles and diaphragm become involved, respiration becomes difficult and death by asphyxia often results.Clostridium perfringens is one of several species of clostridia known to cause gas gangrene and is the causative agent in 95% of gas gangrene cases. The site of infection is usually a wound that comes into contact with C. perfringens spores that germinate in an anaerobic environment. People with poor circulation are more likely to get this disease, due to their inability to keep all of their tissues adequately oxidized. The C. perfringens toxin, which is a phospholipase, attacks cell membranes, causing extensive tissue damage and necrosis, which further reduces the blood supply to the affected area, promoting the spread of the disease. Gas gangrene gets its name from the frequent formation of gas bubbles in the tissue. These gas bubbles are caused by rapid metabolism by C. perfringens, using the muscle tissue as substrate. If untreated gas gangrene will eventually result in a very painful death, as the bacteria slowly eats away at your flesh. Usual treatment is amputation of the infected areas. (From http://microbewiki.kenyon.edu/index.php/Clostridium) (MicrobeWiki: Clostridium)
