Penicillin Was Discovered in a Forgotten Petri Dish — And Sat in Storage for 12 Years

Alexander Fleming returned from a family holiday in Suffolk on September 28, 1928, to his lab at St Mary's Hospital Paddington and found a Petri dish on his bench he had forgotten to clean. The dish had been seeded with Staphylococcus, which had grown over most of it. In one corner a fungal contaminant had also taken hold; around it the bacteria had been killed in a clean halo. Fleming, by his own later account, said "that's funny" and put the dish under his microscope.

The mold turned out to be Penicillium (now identified as P. rubens), and the contamination probably came from the room of his colleague Charles La Touche on the floor below. Fleming spent the next year working out that whatever the mold was secreting killed Gram-positive bacteria without killing white blood cells. He published the result in the British Journal of Experimental Pathology in 1929. The paper was read by almost no one. Even when Fleming presented it at the 1936 International Congress of Microbiology in London, the world's leading bacteriologists were politely uninterested.

The substance he had isolated was unstable and nobody knew how to purify it at scale. The job fell to Howard Florey, an Australian pathologist running a research program at Oxford, and his German émigré biochemist Ernst Chain. Working through the early war years on a shoestring, with deputies including Norman Heatley figuring out a freeze-drying technique that finally produced stable yellow penicillin powder by mid-1942, the Oxford team treated their first patient — an Oxford policeman with a streptococcal infection from a rose thorn — in February 1941. They ran out of supply and the patient died. By the end of the war American pharmaceutical industry had scaled production into the millions of doses. Fleming, Florey, and Chain shared the 1945 Nobel Prize. Fleming's name eclipsed the others in the popular telling.