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Mycotoxin

Mycotoxin

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Mycotoxins are toxic substances produced by molds and fungi such as mushrooms. These toxic substances, which are also known as secondary metabolites, are by-products of metabolism that are not essential to fungal growth. Although some mycotoxins can be used for medicinal purposes, most are poisonous if eaten in sufficient quantity.

Numerous mycotoxins have been studied and identified. Of particular interest are mycotoxins made by fungi that contaminate human foods or by poisonous mushrooms. Many grains, fruits, and vegetables can support fungal growth under certain conditions.

Agricultural attention to mycotoxins has focused on corn, nut, and fruit crops because of their susceptibility to mold growth and their importance in human diet. Climate conditions, including temperature and moisture can affect mold growth in harvested fields, with moister, warmer periods favoring growth. Mycotoxins serve as a defensive force for molds, because they can actually limit the role of competitive microorganisms in the vicinity. Although farm and food industries make every effort to eliminate mycotoxins because they can cause illness and devalue crops, mycotoxins cannot be completely removed, and small quantities of them continue to be present in many foods.

Many mycotoxins affect several target organs including the liver, which develops a toxicity. Mycotoxins harm their host by disrupting cellular activity. The phomopsons, a kind of mycotoxin, inhibit the normal activity of microtubules, essential structures inside cells that are required for cellular division. The Aspergillus family of fungi produce a very potent mycotoxin called aflatoxin. A number of aflatoxins have been isolated, with aflatoxin B (AFB) and aflatoxin G (AFG), an AFB derivative, occurring in greatest quantity. The aflatoxins bind to DNA in the cellular nucleus of the organism they attack, acting as a powerful and potentially fatal, mutagen. Other Aspergillus toxins which have been found in food include ochratoxin A and sterigmatocystin. Ochratoxin A is a mammalian carcinogen that causes renal disease in humans. Like many other naturally occurring mycotoxins, the toxin is found in a number of everyday foods. Varying levels of OA have been detected in beans, cereals, cocoa, coffee, corn, figs, flours, pork kidney, nuts, olives, peas, rice, sausage, and soy.

Mycotoxins can be produced by the fungi that grow on the crop itself, the weeds surrounding the crop, or the soil in which the crop grows. Alternia fungi are natural soil inhabitants that produce several mycotoxinsalternariol and alternariol methyl ether (found on apples), and tenuazonic acid (found on tomatoes and in tomato paste). Alternia toxins are responsible for postharvest decay in these crops. Mycotoxin levels in foods are monitored and minimized by the food industry.

Although most mushrooms are harmless, poisonous mushrooms contain mycotoxins capable of attacking the human host with fatal consequences. The reaction times and symptoms vary according to mushroom. Some mycotoxins act immediatelly on the human host, with effects ranging from nausea, vomiting, hallucination, anxiety, muscle spasms, diarrhea, and hyperactivity or lethargy. The mycotoxins coprine, psilocybin/psilocin, muscarine, and ibotenic acid are all capable of causing these sudden symptoms. Other mycotoxins have more serious effects, are delayed in onset, and can be fatal. The delayed symptoms (which may persist up to 14 days after ingestion) include bloating, headache, severe vomiting, diarrhea, cramps, severe thirst, frequent urination, kidney pain, and death. Potentially fatal mycotoxins that are classified as group A, B, and C poisons include monome-thylhydrazine, the amatoxins, and orellanine.

The mode of action of mushroom-produced mycotoxins varies considerably. Alpha amanitin, amatoxin produced by some species of Amanita, is a class A poison that acts by inhibiting a critical nuclear polymerase that enables the cell to make protein. Once the function of this RNA polymerase is curtailed, basic life processes cease. Attempts to kill alpha amanitin with antibodies have proven to be even more harmful to patients than the poison itself. Most forms of mushroom poisoning can be treated with rapid lavage (induced vomiting) or medically approved ingestion of charcoal to absorb the toxin before it is absorbed into the stomach.

Some cultures have historically sought out milder mycotoxins for their hallucinogenic properties. The class E poisons, psilocybin and psilocin, are found in many Psilocybe species such as Psilocybe cubensis known as magic mushrooms or street mushrooms, these hallucinogens are similar in effect to, but less potent than, the psychedelic drug LSD. The Aztecs of South America used sacred mushrooms for religious rites, and other people from various cultures and times in history have experimented recreationally with mushrooms.

Resources

BOOKS

Diaz, D.E. The Mycotoxins Blue Book. New York: Blackwell Publishers, 2005.

Gorman, Carolyn. Fungus, Mold and Mycotoxins. Northumberland, UK: The Bookworm, 2006.

Johanning, Eckardt. Bioaerosols, Fungi, Mycotoxins and Human Health. Albany, NY: Fungal Research Group Foundation, 2005.

Louise Dickerson

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