Which fungus produces the antibiotic penicillin?

The fungus Penicillium produces the antibiotic penicillin, a family of beta-lactam drugs that stop susceptible bacteria from building their cell walls. In modern commercial production, strains historically classified as Penicillium chrysogenum—and now often identified as Penicillium rubens—are especially important.

Alexander Fleming made the famous observation in 1928 after a Penicillium mould contaminated a culture of Staphylococcus aureus and inhibited bacterial growth nearby. He published the finding in 1929 and named the antibacterial substance penicillin. Howard Florey, Ernst Chain and their colleagues later purified and developed it into a usable medicine, helping transform the treatment of bacterial infections.

The answer is a genus rather than one single species, which is why Penicillium is the fair quiz response. Candida and Saccharomyces are also fungi, but they are not the classic source of penicillin. Aspergillus produces other useful compounds, including some enzymes and medicines, but it is not the fungus associated with penicillin production. Some Penicillium species are also used in cheesemaking.