In what year was penicillin first discovered?

Penicillin was first discovered in 1928 by Scottish physician and bacteriologist Alexander Fleming.

While working at St Mary’s Hospital in London, Fleming noticed that a Penicillium mould had contaminated a culture plate containing Staphylococcus bacteria. Around the mould, the bacteria failed to grow, revealing that the fungus was releasing an antibacterial substance. Fleming investigated the effect and named the substance penicillin.

The discovery did not immediately produce a widely available medicine. Fleming published his findings in 1929, but extracting and purifying penicillin in useful quantities proved difficult. In the late 1930s and early 1940s, researchers at Oxford—including Howard Florey and Ernst Chain—developed methods for studying, purifying, and producing it on a much larger scale.

That distinction explains a common mix-up: 1928 marks Fleming’s discovery of penicillin’s antibacterial activity, while the drug’s development into a practical treatment happened later. Penicillin became especially important during World War II for treating bacterial infections and helped launch the antibiotic era.

Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine for their work on penicillin and its curative effect in infectious disease.