Toxins

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Toxins

BRIAN HOYLE

Toxins are compounds that are produced and released by a variety of microorganisms and other organisms. Toxins can be fast-acting and, because they are already preformed, do not require the growth of a microorganism in the host. State-sanctioned weaponization programs for various toxins have occurred in the past in many countries, and may be ongoing. As well, toxins are a potent weapon for terrorists.

Bacterial toxins. Toxins are the main disease-causing factor for a number of bacteria. Some examples include Corynebacterium diphtheriae (diptheria), Vibrio cholerae (cholera), Bacillus anthracis (anthrax), Clostridium botulinum (botulism), certain strains of Escherichia coli (hemolytic uremic syndrome), and Staphylococcus aureus (toxic shock syndrome).

Certain species of these bacteria are of particular concern in biological warfare and biological terrorism. As the events of 2001 in the United States demonstrated, powdered preparations of Bacillus anthracis spores was easily delivered to a target through the mail. The dispersal of the spores in the air and the inhalation of the spores can cause a form of anthrax that develops quickly and, without treatment, is almost always fatal. The bacteria in the genus Clostridium also form spores. Additionally, during the 1990s, a strain of Staphylococcus aureus emerged that is resistant to almost all known antibiotics.

Bacterial toxins have a wide variety of activity. Some toxins damage the cell wall of host cells, either by dissolving the wall or by chemically punching holes through the wall. Examples of such toxins are the alpha toxin of Clostridium perfringens, hemolysin of Escherichia coli, and streptokinase of Streptococcus pyogenes. The damage to the host cells allows the bacteria to spread rapidly through the host. This can cause an overwhelming infection.

Other bacterial toxins kill host cells by stopping the manufacture of protein in host cells or by degrading the proteins. Examples of protein blockers include exotoxin A of Pseudomonas aeruginosa and the Shiga toxins produced by both Escherichia coli and Shigella dysenteriae. Protein degrading toxins include those produced by Bacillus anthracis and Clostridium botulinum

Still other toxins stimulate an immune response of the host that is so strong that it can damage the host. Staphylococcus aureus produces at least three different toxins that have this effect (i.e., toxic shock syndrome).

Marine toxins. Microorganisms called dinoflagellates can produce toxins when they grow in species of shellfish. Usually, the toxins are a concern when the contaminated seafood is inadvertently eaten. But, the toxins can be isolated in pure form. The purified toxins will produce illness when deliberately used.

Aflatoxin. Aflatoxin is produced by two species of moldAspergillus flavus and Aspergillus parasiticus. The toxin is especially a concern when potatoes are contaminated by the mold. Ingestion of the contaminated potatoes can cause serious, even fatal illness. This toxin is of particular concern for food supplies. Storehouses of produce like potatoes are susceptible to the malicious release of the molds.

Ricin. Ricin is a toxin that is produced by the castor bean. It is the third most deadly toxin that is known, after the toxins produced by Clostridium botulinum and Clostridium tetani. The symptoms of ricin toxin include nausea, muscle spasms, severe lung damage, and convulsions. These symptoms appear within hours, and, without treatment, death from pulmonary failure can result within three days. There is no vaccine or antidote for the toxin.

Ricin has long been a weapon of espionage and terrorism. The most famous use of ricin occurred in 1978, when Georgi Markova recently defected Bulgarian officialwas killed by KGB agents on a bridge in London. An umbrella tip was used to inject a capsule of ricin into one of his legs.

The planned use of ricin by al-Qaeda has been alleged. Traces of ricin have been found in caves in Afghanistan that were used by al-Qaeda. Iraq is also suspected of using ricin in its weaponization program of the 1990s. Also, in January 2003, British antiterrorism officers seized a quantity of ricin in London from a group of Algerian men suspected of being terrorists.

Toxoid vaccines. Some toxins that are capable of causing much harm are also a source of protection. Because of its potency, a toxin cannot be used protectively in its unaltered form. Toxins can be altered, however, so that they do not produce the undesirable effects, but which still stimulate the immune system to produce antibodies to a critical part of the toxin molecule. The weakened version of a toxin is called a toxoid.

The anthrax vaccine that is currently licensed for use contains two toxoids in addition to other immune stimulating molecules. The immune response will produce antibodies to the two toxins of the anthrax bacterium.

FURTHER READING:

PERIODICALS:

Schmitt, C. K., K. C. Meysick, and A. D. O'Brien. "Bacterial Toxins: Friends or Foes?" Emerging Infectious Diseases no. 5 (1999): 22434.

ELECTRONIC:

Centers for Disease Control and Prevention. "Marine Toxins." Division of Bacterial and Mycotic Diseases. June 10, 2002. <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/marinetoxins_g.htm>(29 January 2003).

United States Department of Agriculture. "Aflatoxin." USDA Grain Inspection, Packers and Stockyards Administration. September 17, 1998. <http://www.usda.gov/gipsa/newsroom/backgrounders/b-aflatox.htm>(29 January 2003).

University of Wisconsin at Madison. "Mechanisms of Bacterial Pathogenicity: Protein Toxins." Bacteriology at UW-Madison. 2002. <http://www.bact.wisc.edu/Bact330/lecturept>(30 January 2003).

SEE ALSO

Biocontainment Laboratories
Biosensor Technologies
Food Supply, Counter-terrorism

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Toxins

Toxins are harmful compounds that are produced and released by a variety of microorganisms and other organisms. Toxins can be fast-acting and, because they are already pre-formed, do not require the growth of a microorganism in the host. The illness and death that result from exposure to a variety of toxins make their detection a central part of forensic science .

Toxins are the main disease-causing factor for a number of bacteria. Some examples include Coryne-bacterium diphtheriae (diptheria), Vibrio cholerae (cholera), Bacillus anthracis (anthrax ), Clostridium botulinum (botulism), certain strains of Escherichia coli (hemolytic uremic syndrome), and Staphylococcus aureus (toxic shock syndrome).

Certain species of these bacteria are of particular concern in biological warfare and biological terrorism. As the events of 2001 in the United States demonstrated, powdered preparations of Bacillus anthracis spores were easily delivered to a target through the mail. The dispersal of the spores in the air and the inhalation of the spores can cause a form of anthrax that develops quickly and, without treatment, is almost always fatal. The bacteria in the genus Clostridium also form spores. Additionally, during the 1990s, a strain of Staphylococcus aureus emerged that is resistant to almost all known antibiotics .

Bacterial toxins have a wide variety of activity. Some toxins damage the cell walls of host cells, either by dissolving the wall or by chemically punching holes through the wall. Examples of such toxins are the alpha toxin of Clostridium perfringens, hemolysin of Escherichia coli, and streptokinase of Streptococcus pyogenes. The damage to the host cells allows the bacteria to spread rapidly through the host. This can cause an overwhelming infection.

Other bacterial toxins kill host cells by stopping the manufacture of protein in host cells, or by degrading the proteins. Examples of protein blockers include exotoxin A of Pseudomonas aeruginosa and the Shiga toxins produced by both Escherichia coli and Shigella dysenteriae. Protein degrading toxins include those produced by Bacillus anthracis and Clostridium botulinum

Still other toxins stimulate an immune response of the host that is so strong that it can damage the host. The toxic shock syndrome associated with Staphylococcus aureus results from a host hyperimmune response to three of the bacterial proteins.

Other microorganisms also produce toxins. Marine microorganisms called dinoflagellates can produce toxins when they grow in species of shellfish. Eating the toxic shellfish can cause serious illness.

Some species of mold produce aflatoxin . Aspergillus flavus and Aspergillus parasiticus are aflatoxin-producing molds. The toxin is especially a concern when potatoes are contaminated. Ingestion of the contaminated potatoes can cause serious, even fatal illness.

Ricin is a toxin that is produced by the castor bean. It is the third most deadly toxin that is known, after the toxins produced by Clostridium botulinum and Clostridium tetani. The symptoms of ricin toxin include nausea, muscle spasms, severe lung damage, and convulsions. These symptoms appear within hours, and, without treatment, death from pulmonary failure can result within three days. There is no vaccine or antidote for ricin toxin.

Some toxins that are capable of causing much harm are also a source of protection. Because of its potency, a toxin cannot be used protectively in its unaltered form. Toxins can be altered, however, so that they do not produce the undesirable effects, but still stimulate the immune system to produce antibodies to a critical part of the toxin molecule. The weakened version of a toxin is called a toxoid.

The anthrax vaccine that is currently licensed for use contains two toxoids in addition to other immune stimulating molecules. The immune response will produce antibodies to the two toxins of the anthrax bacterium.

see also Aflatoxin; Biosensor technologies; Botulinum toxin; Food supply; Pathogens; Thin layer chromatography.

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Toxins

Toxins are chemicals or physical agents that exert a toxic effect on living organisms. Toxic means poisonous: that is, causing a reaction with cellular components that disrupts essential metabolic processes. At some level of exposure, all chemicals, whether natural or synthetic, are toxic. All can either cause death or damaging effects soon after exposure, or can cause some other disease (such as cancer or birth defects ) after longer-term exposure.

Although many people think toxins are mainly pesticides or industrial chemicals, they also include the poisons of marine animals, spiders, snakes, plants, and the extremely toxic botulinum toxins that can kill a human being with a single minuscule dose. Toxins can exert their effects on many different organs. The nervous system, the brain, the lungs, the skin, and the eyes are only some of the organs that can be damaged by toxins. Toxicologists use reports, epidemiology , and laboratory studies to characterize both the lethal doses of toxins and the doses of certain chemicals that can cause disease over the long term. Environmental laws regulate exposures to certain human-made toxins.

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toxins A term applied to poisons which are toxic to the human body. Many come from microorganisms — for example, cholera toxin and tetanus toxin are derived respectively from Vibrio cholera and Clostridium tetani. Some toxins are derived from higher organisms — the deadly tetrodotoxin, which blocks nerve conduction, is derived from the liver and ovaries of the puffer fish. Yet others are of fungal origin, such as the liver toxic substance aflatoxin, from a fungus which grows on groundnuts.

Alan W. Cuthbert


See immunization; microorganisms; poisons; toxicology.
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toxin Poisonous substance produced by a living organism. The unpleasant symptoms of many bacterial diseases are due to the release of toxins into the body by bacteria. Many moulds, some larger fungi, and seeds of some higher plants produce toxins. The venom of many snakes contains powerful toxins. See also fungus; snakebite

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toxin A poison produced by a living organism, especially a bacterium. An endotoxin is released only when the bacterial cell dies or disintegrates. An exotoxin is secreted by a bacterial cell into the surrounding medium. In the body a toxin acts as an antigen, producing an immune response.

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toxin (toks-in) n. a poison produced by a living organism, especially by a bacterium (see endotoxin, exotoxin). In the body toxins act as antigens (see antitoxin).

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tox·in / ˈtäksin/ • n. an antigenic poison or venom of plant or animal origin, esp. one produced by or derived from microorganisms and causing disease when present at low concentration in the body.

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toxin
1. Any poisonous substance of plant or animal origin.

2. A microbial product which is poisonous to animals or plants. The symptoms of many types of human disease are the result of the production of one or more toxins by the pathogen. Toxins usually act at specific sites in the body (e.g. neurotoxins affect nerves, enterotoxins affect the gut).