Penicillium is a large genus of fungi that are in the air, in soil and frequently on bread and produce. Different species of these fungi produce many types of secondary metabolites, ranging from the antibacterial drug penicillin to the antifungal drug griseofulvin, along with many compounds that are toxic to humans and animals. Several species are plant pathogens and cause fruit to rot, and one type causes a human disease in areas of Asia. Other species of these fungi have commercial uses, such as being used to produce several different types of cheese or various types of industrial chemicals. It is frequently the first type of mold to colonize water damaged houses and can cause serious illnesses in the inhabitants.
There are approximately 200 species of this filamentous fungus, many of which give off a musty odor. Given the diversity of species, there are many different molecules produced by the members of this genus. The production of secondary metabolites by these fungi is thought to confer a competitive advantage against other organisms in the soil. The most famous is penicillin, the first antibacterial drug to be discovered. The discovery and commercial development of this medicine was so momentous that it earned the 1945 Nobel Prize in Medicine for the trio of scientists involved in its discovery and subsequent large-scale production.
Penicillin was discovered accidentally by Alexander Fleming as Penicillium mold contaminating a culture plate of bacteria. Fleming noticed that there was a clear zone around the fungi where the bacteria had died. He pursued this observation and isolated penicillin from Penicillium notatum. Large quantities were needed to treat soldiers during World War II, and scientists searched feverishly for strains of the fungus that would produce greater amounts of the antibiotic. Penicillium chrysogenum was discovered on a cantaloupe and was found to produce a much higher level of the drug. Mutant fungi that produced even larger quantities of penicillin were created by treating the fungi with radiation.
Another secondary metabolite of use in medicine is the antimicrobial compound griseofulvin, which inhibits the growth of other types of fungi. By contrast, many other products made by fungi of this genus are mycotoxins — fungal compounds that are toxic to animals, including humans. One such compound is patulin, produced by the plant pathogen Penicillium expansum that causes apples to rot. For this reason, it is unwise for a person to eat moldy apples. Several species are pathogens of plants, but many others will grow on stored food such as cereal, as well as fruit and vegetables kept in a refrigerator.
All of the species in these genus produce spores known as conidia that disperse into the air. The name for the genus is derived from the Latin word for “brush,” describing the appearance of the spore clusters. Penicillium marneffi, a human pathogen, can also grow like yeast within the human body. This pathogenic fungus is found in Southeast Asia and can cause severe infections on inhabitants and travelers who have suppressed immune systems, such as those who have acquired immunodeficiency syndrome (AIDS).
Many members of the Penicillium genus are used to produce industrial chemicals such as tartaric, citric and gluconic acids, along with a variety of enzymes. They are used in the food industry to produce cheeses such as Roquefort and Camembert. Also, Penicillium fungi can be an ingredient in sausages and ham to help prevent other organisms from colonizing the meat.
Frequently, this fungi is one of the first to grow when there has been water damage to a house. The fungal spores are so common in the environment and grow on everything from leather to produce to carpeting, so they are able to quickly colonize material when it becomes damp. Many people are allergic to the spores of this fungus and can become very ill if they are subjected to large quantities of the mold, especially over time. In extreme cases, patients might develop severe lung disorders.