Today in History—September 3: Alexander Fleming Finds Penicillin

On this day in 1928, Alexander Fleming returned home to London from a lengthy family vacation at his country house in Suffolk. He’d left his lab at St. Mary’s Hospital in its usual state of disarray, with petri dishes and plates of Staphylococcus aureus stacked in a corner, some of them uncovered.

The Scottish bacteriologist noticed something different about one of them—a kind of blue-green fungus had grown, and it seemed to have inhibited the growth of the bacteria.

Where did the fungus come from? Maybe Fleming had left a window open. Maybe a spore had drifted up from the mycology lab. Regardless, there was a ring around the mold where the bacteria had not grown. He first called this “mould juice” (naturally), and he (correctly) suspected that it had antibacterial properties.

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Fleming was fresh off his work in World War I, where, as a captain in the Army Medical Corps, he’d seen the damage that harsh antiseptics were doing. He’d observed that, despite the use of these chemicals in deep wounds, patients still suffered sepsis and died. Fleming maintained that keeping wounds clean using a mild saline solution promoted better healing, and he was right. He saw firsthand that the world had a great need for a different kind of antibacterial agent.

He identified the mold in his dish as Penicillium notatum, from which we get the substance’s more common name: penicillin. (Later taxonomic study reclassified the exact species.)

Here’s the thing about this story: This wasn’t even the first discovery Fleming alleged he’d made via the magical-surprise route. And it’s worth noting that other scientists struggled to replicate Fleming’s accidental discovery, despite years of trying. But it’s what he said happened—and discover penicillin he did, regardless of the exact truth of the meet-cute.

During World War II, other scientists built on Fleming’s discovery—he’d found penicillin difficult to purify, isolate, and reproduce—and eventually made the world’s first practical antibiotic, saving countless lives ever since.

Famous Birthdays

1499: Diane de Poitiers—French noble and mistress of Henry II who held court as queen of France

1914: Dixy Lee Ray—American zoologist and government official on the Atomic Energy Commission

1938: Noyori Ryōji—Japanese chemist

1971: Kiran Desai—Indian-born American author