Who discovered penicillin after observing mold inhibit bacteria in 1928?

Alexander Fleming discovered penicillin after observing mold inhibit bacteria in 1928. Fleming returned from holiday to find that a mold contaminant had created a clear zone around itself on a culture plate of Staphylococcus bacteria. He identified the mold as Penicillium and named the antibacterial substance penicillin.

Fleming published his findings in 1929, but turning the observation into a practical medicine required further work. Researchers at Oxford, notably Howard Florey and Ernst Chain, developed methods to purify and produce penicillin in useful quantities during the early 1940s. Large-scale manufacture then made it available for treating wounded soldiers and civilians during the Second World War.

A common mix-up is to credit Fleming alone with the finished drug. Fleming made the crucial discovery, while the Oxford team and industrial partners enabled clinical use and mass production. Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine for their work on penicillin and its curative effect in infectious diseases.