Penicillin and other antibiotics are in fact mycotoxins. At the time I found out I was surprised to learn that alcohol is also a mycotoxin. You may be wondering what a mycotoxin is and where does it come from? Penicillium is actually a mold found commonly in soil and many fruits. It is fungi such as molds and yeast that excrete substances called mucotoxins. They are chemicals fungi produce to kill or limit the growth of other organisms, such as bacteria, that compete with fungi for nutrients.