Alexander Fleming discovered penicillin in September 1928 and was not able to turn it into a medicine. He lacked the chemistry, the funding, and probably the interest. Thirteen years later, a team at Oxford led by Howard Florey and Ernst Chain produced the first usable supplies, and the first patient treated in 1941 survived an infection that would otherwise have killed him. So who discovered penicillin depends on what you mean by discover, and the answer is both, unevenly.
Fleming’s Contaminated Plate, 1928
Fleming was a bacteriologist at St Mary’s Hospital in London, studying staphylococci. Returning from a holiday in early September, he found that a culture plate he had left out had grown mould, and that the bacteria around the mould had been destroyed while those farther away were untouched.
The mould was identified as Penicillium notatum, and Fleming named the active substance penicillin. He published in the British Journal of Experimental Pathology in June 1929. The paper attracted almost no attention.
It was not his first such observation. In 1922 he had found that his own nasal mucus inhibited bacterial growth and identified the enzyme responsible, lysozyme — but that had no therapeutic use either.
Why Fleming Could Not Make It Work
The problem was production and purification. Penicillin is produced in tiny quantities by the mould, is chemically unstable, and Fleming had no way to isolate it in usable amounts. He was a bacteriologist; the chemistry needed was someone else’s specialty.
He kept the culture for years and used it in the lab to select bacteria, but he never mounted the effort needed to make a drug. By 1940, more than a decade after the discovery, no patient had ever been treated with penicillin.
Florey, Chain, and the Oxford Team, 1938-1941
Howard Florey, an Australian pathologist at Oxford’s Sir William Dunn School of Pathology, began a systematic survey of antibacterial substances. He brought in Ernst Chain, a German-Jewish biochemist who had fled Nazi Germany in 1933, to handle the purification — the job Fleming had never managed.
By 1940 the team, which also included Norman Heatley, had produced enough penicillin to test in animals. The results were striking: mice given otherwise lethal doses of streptococci survived if they received penicillin. Heatley’s contribution was central — he designed the assay and later the extraction process that made scale-up conceivable. He is routinely left out of the short version of the story.
The First Patients, 1941
In February 1941, Albert Alexander, a 43-year-old police constable with a severe infection from a scratch, became the first person treated with penicillin. He improved dramatically within a day. But supplies ran out, and he died. The team had perhaps a fraction of a full course.
The lesson was production, not efficacy. The group began growing the mould in whatever vessels they could find — bedpans, milk churns, food tins — and by late 1941 had enough to treat a small number of patients successfully.
| Year | Event |
|---|---|
| 1928 | Fleming notices bacterial death around mould on a contaminated plate |
| 1929 | Fleming publishes; the paper is largely ignored |
| 1939 | Florey and Chain begin purification work at Oxford |
| 1940 | First successful animal trials; enough drug for human testing |
| 1941 | Albert Alexander becomes the first treated patient |
| 1944 | US industrial fermentation supplies D-Day casualties |
| 1945 | Fleming, Florey, and Chain share the Nobel Prize |
The Wartime Scale-Up
Florey and Heatley took the work to the United States in 1941, and American industry did what Oxford benches could not. Deep-tank fermentation, a better strain of mould — famously found on a cantaloupe in Peoria, Illinois, in 1943 — and substantial government funding took production from milligrams to tonnes.
By D-Day in June 1944 there was enough penicillin to treat every Allied casualty who needed it. Tens of thousands of lives were saved. Penicillin went from laboratory curiosity to industrial product in about four years.
Who Got Credit
Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine. Heatley was not included, though he received recognition much later in life.
Which is why the question of who discovered penicillin has two defensible answers. Fleming noticed it; Florey and Chain made it a medicine. Both halves were necessary, and the popular version — Fleming alone, in a moment of happy accident — leaves out the decade of chemistry that turned an observation into a drug.
Keep Exploring
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