Mycotoxins - Medical Botany - Lecture Slides, Slides of Botany and Agronomy

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Poisonous Plants, Fungi, and

Algae

II – Mycotoxins

Fungal toxins

• Fungi produce a tremendous diversity of

toxic compounds

• Mushroom toxins formed in the fleshy fruiting bodies of higher fungi
• Mycotoxins formed by hyphae of common molds growing under a variety of conditions

Mycotoxins

• More commonly -- mycotoxins develop in storage and remain within the food after processing and cooking
• Many common indoor environmental contaminants are toxigenic - able to produce toxins
• Some studies revealed significant levels of airborne mycotoxins in occupational settings, offices, and even homes

Health effects of mycotoxins

• Acute and chronic effects on both humans and livestock
• Mycotoxins are believed to be among the most potent known carcinogens
• Majority of research focused on health effects following ingestion of contaminated food
• Effect range from immediate toxic responses and immunosupression to potential long-term teratogenic, estrogenic, and carcinogenic effects.
• Possible health effects due to airborne exposure (exposure to airborne spores with mycotoxins)

Aflatoxins

• Aflatoxin: A ( aspergillus ) - fla ( flavus ) - toxin
• Four toxins soon identified: aflatoxin B1, B2, G1, G
  • (B and G refer to blue or green florescence under uv-light)
• Today known to be 10 aflatoxins
• Aflatoxin B1 most important - highly carcinogenic and widespread occurrence in foods

Sources of aflatoxins

• Produced by 3 species of Aspergillus: A. flavus,

A. parasiticus, A. nomius

• Aspergillus flavus a common fungus that

occurs on grains and legumes

• A. parasiticus most toxigenic species
• Aflatoxins not only toxic but also carcinogenic,

mutagenic, and teratogenic

Aflatoxin B1 is Mutagenic

• Hepatocellular carcinoma (HCC) is a major cause of mortality in certain areas of the world
• About 50% of the HCC cases in parts of the world where food is contaminated with AFB1show a mutation in codon 249 of p53 tumor suppressor gene
• Mutation consists of transversion of G->T in the third position of codon resulting in serine instead of arginine - lab studies confirm

Aflatoxins in corn

• Contamination occurs both in the field before harvest and in storage
• Most researchers agree is that if the contamination is prevented before harvest the problem can be managed
• Emphasis is placed on preventing A flavus infections of the corn by developing disease resistant varieties and also by insect control to prevent initial infections at wound sites

Economic impact

• Because of enforced limits the presence of aflatoxins can have serious economic implications
• In 1980 nearly 66% of random corn samples from North Carolina had concentrations exceeding 20 ppb resulting in a $31 million loss to producers and handlers
• When cows and goats are fed grains contaminated with aflatoxins, they produce milk with aflatoxins - as a result, limits exist for livestock feed but not as low

Average yearly level of aflatoxin contamination from corn grown along the coastal plain of Georgia

Years Concentration of Aflatoxin (ng/g)

1977 622

1978 57

1980 204

1981 37

1983 128

1984 37

1990 217

Aflatoxin production

• Aflatoxins are produced under certain

conditions but only by some strains

• Nontoxigenic strains of A. flavus used to

prepare fermented foods in the orient

Other mycotoxins

• Today over 400 mycotoxins have been

identified from 150 species of fungi with new ones discovered each year

• Species of Aspergillus, Penicillium, Fusarium,

Alternaria, Cladosporium and Stachybotrys form mycotoxins

Common toxigenic fungi

Aspergillus

Penicillium

Stachybotrys

Fusarium

Ochratoxins

• Produced by species of Aspergillus such as A spergillus ochraceus
• Most important is Penicillium verrucosum which occurs on grains
• Ochratoxin A a nephrotoxin responsible for nephropathy in pigs and probably humans
• It is immunosuppressive and also assumed to be carcinogenic in humans - in animal studies it is one of the strongest carcinogens