MYCOTOXINS

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Mycotoxins are exotoxins produced by fungi. The area of microbiology that studies fungi and the toxins they produce (i.e., mycotoxins) is known as mycotoxicology. The disease condition provoked by the intake of mycotoxins in human or animal hosts is generally known as mycotoxicoses. Mycotoxins are pharmacologically active secondary metabolites produced by toxin-producing (pathogenic) fungi in food including stored grains and cereal crops. These exotoxins have the potential to stimulate lethal reactions in humans or animals that consume such toxin-infested food. When taken in large doses and allowed to accumulate in the body system, mycotoxins can elicit several acute and chronic intoxifications and other physiological reactions in human hosts.

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Mycotoxins are mainly secreted by some specific fungal species especially moulds and some mushrooms such as Aspergillus species, Penicillium species, Fusarium species, Claviceps species and Acremonium coenophialum (Table 1).

Table 1. Synopsis of mycotoxins produced by fungi

OrganismMycotoxin producedEffect
Aspergillus flavusAflatoxins  Aflatoxins possess mutagenic, teratogenic, immunosuppressive and carcinogenic activity.
Penicillium speciesOchatoxin A and patulin  Ochatoxin A is a carcinogenic and protein synthesis inhibitor. Patulin promotes apoptosis in cells.
Fusarium speciesFumonisins, deoxynivalenol, zearalenone These mycotoxins promote cellular damage and oxidative stress in cells. They also possess carcinogenic activity.
Acremonium coenophialumErgopeptine alkaloids  Ergopeptine alkaloids cause abortion, gangrene, convulsion, and suppression of lactation in animals such as sheep and cattle.
Amanita phalloides  AmatoxinsAmatoxins are toxic lethal peptides that cause severe vomiting and diarrhea. Degenerative changes occur in the kidney and liver; and death may occur few days after intoxifications.
Adapted with modification from: Hussaini Anthony Makun (2013). Mycotoxin and food safety in developing countries. InTech Publishers, Rijeka, Croatia. Pp. 77-100.

Apart from secreting potent harmful toxins, most Aspergillus species especially A. niger are common contaminants found in the microbiology  laboratory; and they are notorious in colonizing culture media plates that are not properly stored (Figure 1).

Figure 1. Illustration of Aspergillus niger (arrow) growing on Sabouraud dextrose agar (SDA) plate. Photo courtesy: https://www.microbiologyclass.com

Mushrooms (for example, Amanita species) produce a variety of mycotoxins; and the disease condition they cause is known as mycetismus. Mycetismus is known as mushroom poisoning; and it results from the consumption of toxic substances (released as secondary metabolites) from wild mushrooms. It can also occur following contact with wild mushrooms. Diarrhea, vomiting, abdominal pain, fever and nausea are some of the signs of mycetismus.

The main route of entry of mycotoxins into the body is through the ingestion of mycotoxin-contaminated foods. Most fungal mycotoxins are produced in dried food products such as nuts, cereals, maize and other grains and food products especially when stored poorly. Other groups of food especially fruits (for example, oranges, apple, mangoes) as well as vegetables are not left out as they could be contaminated by fungal toxins. Mycotoxins are heat-stable or resistant to heating, and thus most food preparation techniques such as boiling may have little or no effect on their in vivo effectiveness. Thus, it is critical to avoid fungal infestation of food products instead of exposing them to conditions that encourage the growth of moulds in them. Moisture and humid conditions are important factors that stimulate the production of mycotoxins in stored food or grains.

Utmost care is required in the processing and preparation of food meant for human consumption because of the ubiquity of fungal spores in the natural environment. Fungal spores including their toxic mycotoxins are normally produced during the normal metabolic activities of fungi. High humidity and moist environment as well as low temperature conditions are some of the environmental factors that encourage the growth of moulds in food products and in the environment. Fungi easily contaminate food products especially crop plants because fungi are ubiquitous in the soil. And stored food products such as grains and cereals are mostly affected by these environmental fungi that also have some pathological effects because of their ability to produce mycotoxins – which causes mycotoxicoses in the consumers.

Further reading

Anaissie E.J, McGinnis M.R, Pfaller M.A (2009). Clinical Mycology. 2nd ed. Philadelphia, PA: Churchill Livingstone Elsevier. London.

Baumgardner D.J (2012). Soil-related bacterial and fungal infections. J Am Board Fam Med, 25:734-744.

Calderone R.A and Cihlar R.L (eds). Fungal Pathogenesis: Principles and Clinical Applications. New York: Marcel Dekker; 2002.

Champoux J.J, Neidhardt F.C, Drew W.L and Plorde J.J (2004). Sherris Medical Microbiology: An Introduction to Infectious Diseases. 4th edition. McGraw Hill Companies Inc, USA.       

Gladwin M and Trattler B (2006). Clinical Microbiology Made Ridiculously Simple. 3rd edition. MedMaster, Inc., Miami, USA.

Larone D.H (2011). Medically Important Fungi: A Guide to Identification. Fifth edition. American Society of Microbiology Press, USA.

Madigan M.T., Martinko J.M., Dunlap P.V and Clark D.P (2009). Brock Biology of Microorganisms, 12th edition. Pearson Benjamin Cummings Inc, USA.

Stephenson S.L (2010). The Kingdom Fungi: The Biology of Mushrooms, Molds and Lichens. First edition. Timber Press.

Sullivan D.J and Moran G.P (2014). Human Pathogenic Fungi: Molecular Biology and Pathogenic Mechanisms. Second edition. American Society of Microbiology Press, USA.

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