Friday, 8 February 2019

Mycotoxins

Mycotoxins


The assessment of the relationship between species and mycotoxins production has proven to be very difficult. The modern literature is cluttered with examples of species purported to make particular mycotoxins, but where the association is incorrect. In some cases, mycotoxins have even been named based on an erroneous association with a particular species: verruculogen, viridicatum toxin and rubratoxin come to mind. As time has gone on, and more and more compounds have been described, lists of species-mycotoxin associations have become so large, and the inaccuracies in them so widespread in
acceptance, that determining true associations has become very difficult. It does not need to be emphasised how important it is that these associations be known accurately. The possible presence of mycotoxigenic fungi in foods, and rational decisions on the status of foods suspected to contain mycotoxins, are ever present problems in the food industry around the world.

In defining mycotoxins, we exclude fungal metabolites which are active against bacteria, protozoa, and lower animals including insects. Furthermore we exclude Basidiomycete toxins, because these are ingested by eating fruiting bodies, a problem different from the ingestion of toxins produced by microfungi. The definition of microfungi is not rigorous, but understood here to refer principally to Ascomycetous fungi, including those with no sexual stage. 

This paper sets out to provide an up to date authoritative list of mycotoxins which are known to have caused, or we believe have the potential to cause, disease in humans or vertebrate animals, and the fungal species which have been shown to produce them.

We believe that all of the important and known mycotoxins produced by Aspergillus, Fusarium and Penicillium species have been included in this list. However, it is possible that other species will be found which are capable of producing known toxins, or other toxins of consequence will arise. It is also important to note that there are many errors in the literature concerning the mycotoxins and the fungi which produce them (Frisvad et al., 2006).

Many other toxic chemicals, known to be produced by species from these genera, have been excluded from this list for one reason or another. The very toxic chemicals, the janthitrems, have been excluded from this list because the species which make them, including P. janthinellum, normally do not grow to a significant extent in foods. On the other hand Penicillium tularense has recently been demonstrated to produce janthitrems in tomatoes (Andersen and Frisvad, 2004), so maybe these mycotoxins may occur sporadically. Other compounds which occur quite commonly in foods, including mycophenolic acid (Lafont et al., 1979, Lopez-Diaz et al., 1996; Overy and Frisvad, 2005), are of such low acute toxicity to vertebrate animals that their involvement in human or animal diseases appears unlikely. On the other hand mycophenolic acid has been reported to be strongly immunosuppressive (Bentley, 2000), so this fungal metabolite could pave the way for bacterial infections. Toxic low molecular weight compounds that may not be considered mycotoxins in a strict sense include aflatrem, botryodiploidin, brefeldin A, chetomin, chetocins, emestrin, emodin, engleromycin, fusarin C, lolitrems, paspalicine, paspaline, paspalinine, paspalitrems, paxilline, territrems, tryptoquivalins, tryptoquivalons, verruculotoxin, verticillins, and viridicatumtoxin which are among the fungal secondary metabolites listed as mycotoxins by Betina (1989).Future research may show that some of these are more important for human and domestic animals health than currently indicated.

For convenience the list below has been set out by genus, but it should be kept in mind that some mycotoxins are common to both Aspergillus and Penicillium species (Samson, 2001). The list below sets out to be encyclopaedic, but at the same time we have indicated, where possible, which species producing a particular toxin are more likely to occur in foods and which are probably of little consequence.

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