Clostridium botulinum is a group of bacteria best known as the main source of botulinum neurotoxin, the cause of botulism in humans. There are several types of botulism. Foodborne botulism is caused by consumption of pre-formed toxin, whereas infant/intestinal (adult) botulism and wound botulism are infections involving toxin formation in situ.
The symptoms of botulism are primarily neurological and frequently begin with blurred vision, continuing to a descending bilateral flaccid paralysis, and in severe cases a flaccid paralysis of the respiratory or cardiac muscles. In many countries, equine antitoxin is administered to adults suffering from botulism, although in severe cases full recovery may take months or even years. The fatality rate is approximately 5 to 10% of cases. The economic and medical costs associated with foodborne botulism are extremely high.
Clostridium botulinum is defined solely on the basis of an ability to form botulinum neurotoxin, rather than on phylogenetic relationships. This approach is taken in order to emphasize the importance of neurotoxin formation. As a consequence, however, C. botulinum is a heterogeneous "species" that actually comprises four phylogenetically and physiologically distinct clades, known as C. botulinum Groups I to IV, with the distinction among the groups strong enough to merit treatment as four different species. Proteolytic C. botulinum (C. botulinum Group I) and non-proteolytic C. botulinum (C. botulinum Group II) are responsible for most cases of foodborne botulism.
(Peck et al. 2011 and references therein)
Based on research begun in the 1980s, botulinum toxin has been found useful in an expanding list of medical applications that require the blocking of involuntary muscle contractions, including eyelid twitching and other neurological problems. In the late 1980s, it was found that injection of botulinum toxin had cosmetic dermatological applications as well and botulinum toxin entered the cultural mainstream in the United States in the formulation known as Botox® (Kopera 2011)
More information on botulism is available from the U.S.Centers for Disease Control and Prevention.