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Clostridium (Greek for spindle) bacteria produce rugged spores that occur in soils throughout the world. Some are natural inhabitants of mammalian (e.g., human, cattle, horses) intestinal tracts, and are present in their excreta. The organisms are anaerobic, and thrive in anoxic conditions, including rotting organisms. C. botulism, which is named after the Latin word for sausage (botulus), was discovered by Van Ermengen in 1897, who determined its toxicity was caused by a toxin released into ham. He also discovered the bacteria was destroyed by heat, and would not produce in a saline environment. Cases of botulism were increasingly reported with canning in the US, which raised concerns about swollen tin cans, but the incidence of human toxiciy from botulism poisoning in the US was relatively low in the 1930ís and it is now almost negligible.
Botulism is caused by the bacteria, Clostridium botulism, which produces a neurotoxin with seven serological varieties (A-G). The effect of each of those varieties is similar: paralysis of muscles controlled by cholinergic nerve cells due to the prevention of the release of acetylcholine from the nerve endings. Symptoms include blurred vision, respiratory difficulty, nausea, diarrhea and/or constipation, cramps, sore throat, muscle weakness, and paresthesia. The common types in human food borne illness are A, B, E, and F; those causing animal illness are C and D. Types F and G are rare. Types A and some of B and F are proteolytic (i.e., they digest meat to produce a characteristic putrefactive smell), while type E and some types B,C,D, and F are nonproteolytic and may not be detected by a strong odor.
Spores of C. botulism are found world-wide, but the types have characteristic geographic distributions. Type A is most commonly found in the western US, Brazil, and Argentina; proteolytic type B is most common in the eastern US; nonproteolytic type B is most common in the United Kingdom, Denmark and The Netherlands; type E is most common in the northern regions (Scandinavia, Poland, Japan, Russia, Alaska, Canada, and Sweden) and large numbers of its spores (350,000 / kg) have been found in sediments of the Baltic Sea. Consequently, it is likely that the organism actively grows in marine environments, as well as in the St. Lawrence estuary and shallow, brackish lakes.
The bacteria is also present in fish-eating mammals. This has caused outbreaks of botulism in Inuits, when their food is prepared in traditional ways. These involve fermenting blubber and flippers in skin pouches and jars at ambient temperatures, which lead to anaerobic conditions and the subsequent germination and multiplication of the anaerobic bacteria. Any toxin present in the contaminated meat will not be destroyed by freezing, but can be destroyed by thorough cooking. In response to this problem, health authorities now regulate these food product, antitoxins are located in medical stations, and emergency medical evacuation plans are in place throughout the Arctic. Consequently, there are now only an average of 8 cases and 1 death per year due to botulism in northern Canada.
The problem is most common in food processing activities that parallel those of the Inuit. Notably, canning foods without proper heating (e.g., pressure cooker) to kill the organisms and extended storage, which allows the organism to multiply. In the US, this results in losses of over $100 million per year contaminated tuna and salmon, each.
Ingestion of the preformed toxin is not the only cause of botulism. In infant botulism, the bacteria germinates in the gut and produce small amounts of the toxin, which may be debilitating and may be a cause of sudden infant syndrome (SID). The sources of bacteria have not been firmly established, since it has been found in dust and some foods, but the strongest link is in honey. Because of this connection, it is recommended to not feed honey to babies one year or younger.
Prevention of spore germination is attained through (1) heating (250 F)to destruction and (2) inhibition by the presence of oxygen, acidity (pH < 4.6), salt (> 7%), sugar (>50%), nitrites, ascorbates, alcohol, refrigeration, and freezing. For example, canned bacon may be preserved with 7% salt and 120 ppm nitrite.
(1) C. perfrigens is a more common, but less hazardous, cause of food poisoning in the US. (2) C. tetani is the cause of tetanus, which occurs when itís toxin attacks the nervous system in the spinal cord and makes muscles spasms and contraction. This includes a hideous grin (risus sardonicus) or "lockjaw" . While now rare in developed countries (e.g., there were 117 cases in the US in 1989-1990), it was common in Ancient Egypt, where dung was used as a medicine, and in military campaigns, where filthy wounds were common. Neonatal tetanus still causes an estimated 560,000 deaths per year in Asia and Africa, where babyís umbilical cords are cut with non-sterile instruments and the stump is packed with dirt. (3) C. difficile has recently been recognized as a cause of colitis associated with taking antibiotics, which change the balance of bacteria in the gastrointestinal tract. (4) C. pasteurianum symbiotically assists in nitrogen fixation by some plants.
For approximately $350, dermatologists will inject the botulism toxin into your face to paralyze the muscles and smooth out wrinkles. The treatment lasts three to six months.
see web sites on avian botulism in the Salton Sea
Biddle, W. 1995. A Field Guide to Germs. Henry Holt and Company,
New York, NY, 196 pp.
Todd, E.C.D. 1990. Acute illness from environmental food contaminants In: Food contamination from Environmental Sources (J.O. Nriagu and M.S. Simmons, eds.), John Wiley & Sons, Inc. New York, NY, pp. 663-719.
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