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Alexander Fleming
1881–1955 · Bacteriologist
A Scottish bacteriologist who discovered penicillin in 1928, beginning a medical breakthrough that helped transform the treatment of bacterial infections.
“When I woke up just after dawn on September 28, 1928, I certainly didn't plan to revolutionize all medicine by discovering the world's first antibiotic, but I suppose that was exactly what I did.”
Why is this scientist famous?
Discovered penicillin, leading to one of the most important developments in the treatment of bacterial infections.
Fleming discovered that a Penicillium mould contaminating a bacterial culture produced a substance that inhibited bacterial growth. He named that substance penicillin. More than a decade later, Howard Florey, Ernst Chain and their colleagues at Oxford developed penicillin into an effective treatment, and wartime industrial production made it widely available.
Alexander's story
Early Life
Born in 1881 at Lochfield Farm in Ayrshire, Scotland, Fleming was the son of a farmer. He moved to London as a teenager and worked in a shipping office before studying medicine at St. Mary's Hospital Medical School on a scholarship. During the First World War he served as a captain in the Royal Army Medical Corps and continued bacteriological work related to wound infection and antiseptics.
Lysozyme
Before penicillin, Fleming discovered lysozyme in 1921 — an enzyme in tears, saliva, and mucus that kills some bacteria. He discovered it when a drop of his own nose mucus fell onto a bacterial culture and killed it. Though lysozyme only worked on harmless bacteria, it proved that the body has natural antibacterial defences.
The Accidental Discovery
In 1928, Fleming noticed that a culture plate of staphylococci had become contaminated by a Penicillium mould. Around the mould was a clear area where bacterial colonies had been destroyed or inhibited. Fleming investigated the effect and found that the mould released an antibacterial substance, which he named penicillin. He published his findings in 1929.
Mass Production and the Nobel Prize
Fleming was unable to turn penicillin into a practical medicine himself. Beginning in the late 1930s, Howard Florey, Ernst Chain and their Oxford team developed methods for purifying and testing penicillin and demonstrated its therapeutic potential. Large-scale wartime production then involved government, academic and pharmaceutical collaboration. Fleming, Florey and Chain shared the 1945 Nobel Prize in Physiology or Medicine.
What did they discover?
Penicillin
Discovered in 1928 that a Penicillium mould produced a substance that inhibited susceptible bacteria and named the substance penicillin.
Lysozyme
Discovered a natural antibacterial enzyme in tears, saliva, and mucus in 1921, proving that the human body has its own defences against bacteria.
Amazing facts
Fleming's discovery began when he noticed an accidental Penicillium contamination on a bacterial culture plate and investigated the bacteria-free area around the mould.
He also discovered lysozyme — when a drop from his own runny nose fell onto a bacterial culture.
He shared the 1945 Nobel Prize with Howard Florey and Ernst Chain, who figured out how to mass-produce penicillin.
Penicillin and the antibiotics developed after it have saved millions of lives by making many bacterial infections treatable.
He was a skilled painter and used bacteria to create "germ paintings" — artworks made with living bacteria.
Fleming later warned that using too little penicillin could encourage bacteria to become resistant to it.
Timeline
Born at Lochfield Farm, Ayrshire, Scotland on August 6
Qualified as a doctor from St. Mary's Hospital Medical School, London
Served in the Royal Army Medical Corps during the First World War
Discovered lysozyme, a natural antibacterial enzyme
Discovered penicillin when mold contaminated a petri dish on September 28
Published his findings on penicillin, but the discovery was largely ignored at first
Florey, Chain and their Oxford colleagues demonstrated penicillin's therapeutic potential in experimental studies
Large-scale wartime production of penicillin expanded in Britain and the United States
Shared the Nobel Prize in Physiology or Medicine with Florey and Chain
Died in London on March 11, age 73
Awards & honours
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