Fleming's Mold and the Antibiotic Age
A contaminated plate in 1928, then the Oxford team who turned a curiosity into a drug that saved millions
Quick facts
- Fleming's observation
- 1928, Penicillium mold killing bacteria
- Made usable by
- Florey and Chain, Oxford, early 1940s
- Key publication
- The Lancet, August 24, 1940
- Nobel Prize
- 1945, shared by Fleming, Chain, Florey
What happened
A chance event in a London laboratory in 1928 changed the course of medicine. Alexander Fleming, a bacteriologist at St. Mary's Hospital, returned from a vacation and noticed a zone around an invading fungus on an agar plate where the bacteria did not grow. The mold, a Penicillium, was producing something that killed bacteria. Fleming did not take the next steps to purify it or test it as a treatment. That work fell to Howard Florey and Ernst Chain at Oxford: Florey directed that penicillin's antibacterial properties be tested in mice, the decisive step Fleming had not taken, and on August 24, 1940 Florey and Chain reported their findings in The Lancet, describing how to produce and purify penicillin with enough potency to protect infected animals. Penicillin's effects led to the Nobel Prize in Physiology or Medicine in 1945, shared by Fleming, Chain, and Florey.
Why it matters
Penicillin was the first true antibiotic, a drug that could cure bacterial infections that had routinely killed people, and it opened an era in which pneumonia, sepsis, and battlefield wounds became treatable. The story is also a lesson in shared credit: the famous accident was Fleming's, but the medicine came from the Oxford team's methodical development, and both halves were needed.
How we know
Fleming's 1928 observation and the Oxford team's 1940 Lancet report on producing and testing penicillin are documented in the original publications and in institutional and peer-reviewed histories, which also record the shared 1945 Nobel Prize.
Sources
- Emerging Infectious Diseases / medical history (via PMC / U.S. National Library of Medicine). The Discovery of Penicillin—New Insights After More Than 75 Years of Clinical Use · Peer-reviewed (author-declared)pmc.ncbi.nlm.nih.gov · Cited as a "journal" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- Science History Institute. Howard Walter Florey and Ernst Boris Chain · General sourcesciencehistory.org · Cited as a "reference" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
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