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botulinum toxin

Sunday 15 March 2009

Botulinum toxin is a neurotoxic protein produced by the bacterium Clostridium botulinum.

It is the most toxic protein known with an LD50 of roughly 0.005-0.05 µg/kg. Despite this, it is used in minute doses in some parts of the world, to treat muscle spasms.

There are seven serologically distinct toxin types, designated A through G; 3 subtypes of A have been described. The toxin is a two-chain polypeptide with a 100-kDa heavy chain joined by a disulfide bond to a 50-kDa light chain.

This light chain is an enzyme (a protease) that attacks one of the fusion proteins (SNAP-25, syntaxin or synaptobrevin) at a neuromuscular junction, preventing vesicles from anchoring to the membrane to release acetylcholine.

By inhibiting acetylcholine release, the toxin interferes with nerve impulses and causes flaccid (sagging) paralysis of muscles in botulism as opposite to the spastic paralysis seen in tetanus.

It is the most acutely toxic substance known, with a median lethal dose of about 1 ng/kg (intravenously).

Food-borne botulism usually results from ingestion of food that has become contaminated with spores (such as a perforated can) in an anaerobic environment, allowing the spores to germinate and grow. The growing (vegetative) bacteria produce toxin. It is the ingestion of preformed toxin that causes botulism, not ingestion of the spores or vegetative organism.

Proper refrigeration at temperatures below 3 °C (38 °F) prevents the growth of Clostridium botulinum. Clostridium botulinum is also susceptible to high salt and low ph levels.

Infant (intestinal) and wound botulism both result from infection with spores which subsequently germinate, resulting in production of toxin and the symptoms of botulism.

Toxin itself is rapidly destroyed by heat, such as in thorough cooking. However, the spores which produce the toxin are heat-tolerant and will survive boiling at 100 degrees Celsius for an extended period of time.


It is sold commercially under the brand names Botox, Dysport, Myobloc, Neurobloc and Xeomin for this purpose. BOTOX™ Cosmetic and Vistabel are available for cosmetic treatment. The terms Botox (Cosmetic), Vistabel, Dysport, Myobloc, Neurobloc and Xeomin are trade names and are not used generically to describe the neurotoxins produced by C. botulinum.

Botulism (Latin, botulus, "sausage") also known as "Botulinus Intoxication," is a rare but serious paralytic illness caused by botulin toxin. The toxin is produced by the bacteria Clostridium botulinum.

Clostridium botulinum is an anaerobic, Gram positive, spore-forming rod. Botulin toxin is one of the most powerful known toxins: about one microgram is lethal to humans. It acts by blocking nerve function and leads to respiratory and musculoskeletal paralysis.

There are three main kinds of botulism:

- Infant botulism or intestinal botulism is caused by ingesting the spores of the Clostridium botulinum, which then grow inside the infant’s intestines and release toxin.

- Foodborne botulism is caused by eating foods that contain botulin toxin.

- Wound botulism, the least common of the three in developing countries; but is by far the most common cause of botulism in developed countries. It is caused by botulin toxin produced in a wound infected with C. botulinum, and there is a particular association with intravenous drug use and skin popping.

All forms of botulism can be lethal and are always considered medical emergencies. Foodborne botulism can be extremely dangerous as a public health risk because multiple persons can consume the poison from a single contaminated food source.