Clostridium botulinum
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| Clostridium botulinum | ||||||||||||||
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 Clostridium botulinum stained with gentian violet.
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| Clostridium botulinum van Ermengem, 1896 |
Clostridium botulinum is a Gram-positive bacterium that produces the toxin botulin, the causative agent in botulism and the main substance in botox.[1] It is included in the genus Clostridium. C. botulinum was first recognized and isolated in 1896 by Emile van Ermengem and is commonly found in soil.
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[edit] Microbiology
C. botulinum is a rod-shaped microorganism. It is an obligate anaerobe, meaning that oxygen is poisonous to the cells. However, they tolerate very small traces of oxygen thanks to an enzyme called superoxide dismutase (SOD) which is an important antioxidant defense in nearly all cells exposed to oxygen. Under unfavorable circumstances they are able to form endospores that allow them to survive in a dormant state until exposed to conditions that can support their growth.[2]
In laboratory the microorganism is usually aislated in Tryptose Sulfite Cycloserine (TSC) growth media, always in an anaerobic environment with less than 2% of Oxygen. This can be achieved by several commercial kits that use a chemical reaction to replace O2 with CO2 (E.J. GasPak System). C. botulinum is lipase negative microorganism, it grow between pH values of 4.8 and 7 and it can't use lactose as a primary carbon source, characteristics important during a biochemical identification[3]
[edit] Subtypes
Each of the seven serotypes of C. botulinum produces a different botulin toxin.[4] These are labeled with letters and are called A to G types. Types C and D are not human pathogens. A "mouse protection" test determines the type of C. botulinum present using monoclonal antibodies.
In the United States, outbreaks are primarily due to types A or B, which are found in soil, or type E, which is found in fish. Optimum temperature for types A and B is 35-40 °C. Minimum pH is 4.6. It takes 25 min at 100 °C to kill these types. Optimum temperature for type E is 18-25 °C. Minimum pH is 5.0. It takes about 0.1 minute at 100 °C to kill type E C. botulinum.
C. botulinum strains that do not produce a botulin toxin are referred to as Clostridium sporogenes.[5] The species are otherwise phylogenetically indistinguishable, and C. sporogenes is often used as a model for the toxic subtypes.
Clostridium botulinum is also used to prepare Botox, used to selectively paralyze muscles to temporarily relieve wrinkles. It has other "off-label" medical purposes, such as treating severe facial pain, such as that caused by trigeminal neuralgia.
Botulin toxin produced by Clostridium botulinum is often believed to be a potential bioweapon as it is so potent that it takes about 75 nanograms to kill a person (LD50 of 1ng/kg,[6] assuming an average person weighs ~75kg); 500 grams of it would be enough to kill half of the entire human population.
Clostridium botulinum is a soil bacterium. The spores can survive in most environments and are very hard to kill. They can survive the temperature of boiling water at sea level, thus many foods are canned with a pressurized boil that achieves an even higher temperature, sufficient to kill the spores.
Growth of the bacterium can be prevented by high acidity, high ratio of dissolved sugar, high levels of oxygen, or very low levels of moisture. For example in a low acid, canned vegetable such as green beans that are not heated hot enough to kill the spores (i.e., a pressurized environment) may provide an oxygen free medium for the spores to grow and produce the toxin. On the other hand, pickles are sufficiently acidic to prevent growth; even if the spores are present, they pose no danger to the consumer. Honey, corn syrup, and other sweeteners may contain spores but the spores cannot grow in a highly concentrated sugar solution; however, when a sweetener is diluted in the low oxygen, low acid digestive system of an infant, the spores can grow and produce toxin. As soon as infants begin eating solid food, the digestive juices become too acidic for the bacterium to grow.
[edit] External links
[edit] References
- ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0838585299.
- ^ Doyle, Michael P. (2007). Food Microbiology: Fundaments and Frontiers. ASM Press.
- ^ . (2005). Brock Biology of Microorganisms, 11th ed., Prentice Hall. ISBN 0131443291.
- ^ Wells CL, Wilkins TD (1996). Botulism and Clostridium botulinum in: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.
- ^ Judicial Commission of the International Committee on Systematic Bacteriology (1999) Rejection of Clostridium putrificum and conservation of Clostridium botulinum and Clostridium sporogenes Opinion 69. International Journal of Systematic Bacteriology. 49, 339.
- ^ By Diane O. Fleming, Debra Long Hunt. Biological Safety: principles and practices. ASM Press, 2000, p. 267.
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