What Is Penicillium?

Helga George

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.

Penicillium is used to created some cheeses.
Penicillium is used to created some cheeses.

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.

Alexander Fleming accidentally discovered Penicillin from a culture of Penicillium.
Alexander Fleming accidentally discovered Penicillin from a culture of Penicillium.

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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.

Penicillium chrysogenum was discovered on a cantaloupe.
Penicillium chrysogenum was discovered on a cantaloupe.

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 molds can flourish on organic materials, including fruit and other foods.
All molds can flourish on organic materials, including fruit and other foods.

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.

Bread with Penicillium mold.
Bread with Penicillium mold.

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Discussion Comments


In the mid 1890s, Ernest Duchesne identified penicillin glaucum, capable of killing typhoid bacteria. He asked Arab stable boys in Lyons, France why they purposefully allowed mold to grow on saddles. They told him the mold healed saddle sores. Since they used penicillin successfully, the discoverers of penicillin were the Arab stable boys. Duchesne wrote his dissertation about his research into penicillin. The Institute Pasteur of Paris, France refused to even acknowledge receiving the dissertation because Duchesne was 23 years old and unknown. Alexander Fleming received a Nobel Prize in 1949. Edward Duchesne received posthumous recognition in 1949. I seem to be the only person recognizing the Arab stable boys. Alexander Fleming re-discovered penicillin, and his rediscovery was a fortunate accident. Ernest Duchesne paid attention to the Arab stable boys and did his own research. Millions of people died between the Arab stable boys’ discovery in the mid 1890s and the general use of penicillin in the mid 1940s.


What caused the bacteria to stop growing around the fungus spore?


My syllabus requires for me to describe the role of the fungus penicillium in the production of the antibiotic penicillin. Could you please explain this?

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