Fleming Discovers Penicillin: Medicine Changed Forever

Alexander Fleming returned from a summer holiday to find a mess in his laboratory, and the mess changed the course of medicine. On September 28, 1928, the Scottish bacteriologist noticed that a petri dish of Staphylococcus bacteria he had left uncovered before his vacation had been contaminated by a mold. Around the mold, the bacteria were dead. Fleming was working at St. Mary's Hospital in London, where he had spent years studying wound infections and antiseptics. His laboratory was famously untidy, with cultures stacked on benches rather than properly stored. This carelessness turned out to be essential. The contaminating mold, later identified as Penicillium notatum, had likely drifted in through an open window from a mycology lab one floor below. Had Fleming been more organized, he might have simply discarded the spoiled dish. Instead, he investigated. "That's funny," he reportedly said, pointing out the clear zone around the mold to his colleague Merlin Price. Fleming cultured the mold separately and discovered that it produced a substance capable of killing a wide range of disease-causing bacteria, including streptococcus, meningococcus, and the diphtheria bacillus. He named the substance penicillin and published his findings in the British Journal of Experimental Pathology in 1929. The medical establishment barely noticed. Fleming lacked the resources and chemical expertise to purify penicillin into a stable, concentrated form suitable for clinical use. The breakthrough languished for over a decade until Howard Florey and Ernst Boris Chain at Oxford University revisited Fleming's work in 1939. Using techniques from biochemistry and industrial fermentation, Florey and Chain produced enough purified penicillin to begin human trials in 1941. The results were extraordinary: infections that had been death sentences became curable within days. American pharmaceutical companies, mobilized by the wartime need for the drug, scaled production from laboratory quantities to industrial volumes. By D-Day in June 1944, enough penicillin existed to treat every wounded Allied soldier. The drug saved an estimated 200 million lives in the 20th century alone. Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine. Fleming's messy lab bench had launched the antibiotic era.