Alexander Fleming shared the 1945 Nobel Prize in Physiology or Medicine for a discovery that began with an accident. In 1928 he noticed that a mould contaminating one of his bacterial cultures had killed the bacteria around it. The mould produced a substance he named penicillin.
For years the finding sat largely unused until other scientists — Howard Florey and Ernst Chain, who shared the prize — found ways to purify and mass-produce it. By the 1940s penicillin was saving wounded soldiers and civilians from once-fatal infections.
Penicillin opened the antibiotic era, transforming medicine and making routine what had been deadly. Its story is also a caution: overuse has since driven resistance, a challenge modern medicine still works to manage.
Why it matters: Fleming's chance observation launched antibiotics — arguably the single greatest life-saving advance in the history of medicine.
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