Not all species of the Penicillium mold are helpful to humanity. Newly discovered species, such as this one (held by technician Eileen Bayer) have been linked to illness in tropical areas.
Photograph by Keith Weller, USDA, Agricultural Research Service

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  • On September 28, 1928, Scottish scientist Alexander Fleming discovered penicillin, now one of the world’s leading antibiotic medications. Fleming had been studying a strain of bacteria (staphylococci) when he noticed that mold had developed in a Petri dish containing the bacteria. More importantly, a bacteria-free ring surrounded the mold. Fleming experimented with the mold over and over again and found that it stopped the growth of the staphylococci he was studying, as well as a wide variety of germs that cause many infections and illnesses in humans. He named the substance penicillin.

    It took some time for scientists to turn Fleming’s discovery into a drug, and it was not until 1943 that penicillin was produced in large quantities. Fleming won the Nobel Prize in Medicine in 1945 for his discovery.

  • Term Part of Speech Definition Encyclopedic Entry
    antibiotic Noun

    substance that can stop or slow the growth of certain microbes, such as bacteria. Antibiotics do not stop viruses.

    bacteria Plural Noun

    (singular: bacterium) single-celled organisms found in every ecosystem on Earth.

    Encyclopedic Entry: Bacteria
    drug Noun

    chemical substance used to change the physical or mental state of an organism.

    illness Noun

    disease or sickness.

    infection Noun

    disease caused by microscopic organisms, such as bacteria.

    medication Noun

    drug or other remedy used to treat an illness.

    mold Noun

    type of fungi that forms on the surface of materials.

    Nobel Prize Noun

    one of five awards established by the Swedish businessman Alfred Nobel in 1901. Nobel Prizes are awarded in physics, chemistry, medicine, literature, and peace.