Dangers in Mouldy Foods

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Some people are incredibly fussy about their food. When confronted with fruits or vegetables having just the tiniest bit of damage, they either reject it outright or, infuriatingly, carefully cut out the offending bit. What makes this behaviour doubly annoying is that, basically, they are right! Some of the worst toxins in the world are made by the same sorts of moulds (fungi) that can infect your apple. The picture is not simple. Most fungi are not dangerous to us; indeed we couldn’t get many items of our usual diet without the help of fungi. The potentially dangerous fungi don’t always make toxins. Even if there are no visual signs of fungal infection, a past fungal infection (especially in cereal grains) can leave health-damaging residues of mycotoxin without any external evidence of infection.

To be fair, we should first acknowledge the many beneficial aspects of fungi. Fungi are some of our most important collaborators in getting and in processing our foods. Alcohol comes from yeast, a one- celled fungus; Japanese sake relies on a different fungus to transform rice starch into fermentable sugars; bread wouldn’t rise without yeast; and blue cheese owes its colour to a particular fungus. Many economically important plants, from pine trees to orchids, rely on a fine network of fungal threads, searching the soil for nutrients that the plant roots themselves cannot find or cannot extract. Some cooperative fungi live inside a plant and produce protective chemicals to help the plant repel bacteria, insects, and grazing animals.

Probably the most important benefit of fungi is their ability to break down organic matter. The earth’s ecology would come to a grinding halt if the recycling of minerals, in which fungi play an important role, ever stopped, and bits of dead organisms accumulated in the soil instead of rotting down.

Harmful Fungi

Many people also know the problems of fungal infections like thrush and athlete’s foot (Tinea). A common characteristic of fungal infections is that they are difficult to control with most antibiotics. There is some poetic justice here, since so many antibiotics came from fungi. It should not be surprising that fungi, having developed antibiotics to combat bacterial invasion of their turf, are also good at resisting antibiotics made by other fungi. Biologists say that finding new antibiotics is easy, but the tough part is finding an antibiotic that won’t kill the human as well as the bacteria.

Despite their invaluable assistance in certain situations, fungi are perhaps even less human-friendly than plants. Their way of life favours no-holds-barred chemical warfare. As a result, fungi have developed a wide range of exceedingly unpleasant toxins. (Greek-speaking scientists call these ‘mycotoxins’.) About three hundred mycotoxins are known.

Why do fungi make mycotoxins? Frequently they inhibit the growth of other bacteria and fungi that would like to share in the meal. Moreover, the bad taste or unpleasant after-effects of eating infected food may stop big animals like us from eating something that the fungus wants to consume. The mouldy apple that we toss away instead of munching will soon become a mass of grateful fungal strands.

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