Did Fleming invent mass-produced penicillin?

No. Fleming discovered the antibacterial effect in 1928, but it was Florey and Chain's Oxford team, plus American fermentation researchers, who turned it into a medicine that could be manufactured at scale a decade later.

Why did companies agree to share trade secrets they normally guard fiercely?

The War Production Board tied wartime contracts and public standing to visible cooperation, which flipped the incentive: refusing to share became the move that looked bad and risked losing government business, not the safe, cautious choice.

Did the cooperation last after the war?

No. Once the government stopped coordinating the industry and wartime urgency passed, manufacturers returned to competing over patents in the ordinary way.

health · 1928 to 1945

Penicillin's Open Formula: Racing to Share a Wartime Cure

Alexander Fleming found penicillin by accident in 1928, but a wartime shortage of doses forced rival drug companies into a decision no patent lawyer would recommend: pool their production secrets.

Facts drawn from the Nobel Prize archive, the American Chemical Society's landmark history, and a peer-reviewed account of the wartime manufacturing collaboration; interpretive framing is labeled as modeled analysis.

Fleming noticed in 1928 that a mold contaminating one of his petri dishes had killed the bacteria around it, and he published the observation, but he lacked the chemistry to purify or mass-produce the compound. The finding sat mostly unused for over a decade while medicine had no reliable way to treat bacterial infection at scale.

At Oxford, Howard Florey and Ernst Chain led a team that purified the mold's active compound and proved in 1940 that it could cure infected mice, then pushed on to the first human trials. Their colleague Norman Heatley carried a culture to the United States Department of Agriculture's laboratory in Peoria, Illinois in 1941, where researchers found a corn-steep-liquor growth medium and a more productive mold strain that multiplied the yield per batch.

Play the same structure: The Formula Decision.

Sources

[VERIFIED] Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine for the discovery and development of penicillin The Nobel Prize, Nobel Prize in Physiology or Medicine 1945
[VERIFIED] US penicillin production scaled from about 21 billion units in 1943 to about 6.8 trillion units by the end of 1945 American Chemical Society, Penicillin Production through Deep-tank Fermentation, National Historic Chemical Landmark
[VERIFIED] The War Production Board coordinated a data-sharing arrangement among competing manufacturers to scale wartime penicillin output Peer-reviewed history, World War II and the Penicillin Collaborative, PMC
[VERIFIED] Fleming's 1928 discovery and the decade-long gap before Oxford's purification work made it usable The Nobel Prize, Alexander Fleming, Biographical