Clostridium botulinum is a rod-shaped Gram-positive bacterium which produces the most poisonous toxin known. Botulinum toxin has a lethal dose of about 1 ng/kg, meaning that a few hundred grams could theoretically kill every person on earth. The toxin works by blocking the release of acetylcholine, preventing muscles from contracting. In mammals, this leads to repiratory failure and death, although the toxin is slow acting and takes several days to reach its full effect.
Botulism is a severe and often fatal disease of humans and animals, but the symptoms are caused by botulinum toxin rather than by the bacteria itself. Food-borne botulism is caused by eating food contaminated with Clostridium botulinum endospores. However, Clostridia are anaerobic bacteria which do not grow in the presence of oxygen, so the most common source of botulism is improperly canned foods where not all the bacteria have been killed in the canning process, or where perforated cans allow the bacteria to enter and grow in an anaerobic environment. There are around 100 cases of food-borne botulism in the USA each year. Other types of botulism include infant botulism, caused by the toxin released from Clostridium botulinum cells growing in the intestine of newborn infants, and wound botulism which is caused by wounds infected with C. botulinum.
The complete genome sequence of C. botulinum was recently determined (Genome sequence of a proteolytic (Group I) Clostridium botulinum strain Hall A and comparative analysis of the clostridial genomes. Genome Research, DOI: 10.1101/gr.6282807). This study revealed was that C. botulinum has a saprophytic lifestyle in soil and aquatic environments and relies on its potent toxin to rapidly kill a wide range of prey species in order to gain access to nutrient sources, which it then digests by releasing a large number of extracellular enzymes.
There are seven serologically distinct types of botulinum toxin, called A to G. The toxin itself is a two-chain polypeptide with a 100-kDa heavy chain joined by a disulphide bond to a 50-kDa light chain. The light chain is a protease which attacks the fusion proteins at neuromuscular junctions, 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 seen in botulism as opposed to the spastic (rigid) paralysis seen in tetanus (caused by Clostridium tetani).
So botulinum toxin is clearly nasty stuff, and only a lunatic would inject themselves with it. There are in fact a few genuine medical reasons where very small doses of botulinum toxin can be useful, such as prolonged headaches in severe migrane sufferers, and a few surgical operations where carefully controlled use of the toxin can make the operation more successful. This makes it all the more mysterious why botulinum toxin (or Botox) injections are the fastest-growing cosmetic procedure. Botox was first used in 1980 to treat facial muscle disorders such as lazy eyes, facial ticks and uncontrolled blinking. Cosmetic treatments were pioneered in 1987. In small doses, Botox works by paralysing the muscles of the face which are used in frowning and raising the eyebrows. When these muscles relax, the fine lines and wrinkles smooth out. Unfortunately, when too much is used, Botox treatment can leave the face with a lack of expression. And with something as potent as botulinum toxin, there is a very fine line between fewer winkles and facial paralysis. People who undergo too many Botox treatments may develop antibodies to the toxin, so the treatment stops working. 40% of UK patients using Botox expressed a compulsive desire for further treatments and there was a 50% increase in the number of people treated with Botox in the UK during 2005. More than 100,000 Botox treatments are now given in Britain each year, but the UK government recently refused to introduce safety standards for the use of Botox in cosmetic surgery.
Personally, I’m quite happy with my wrinkles, so I don’t think I’ll be paying a lot of money to be injected with the most poisonous substance ever discovered any time soon!