Who discovered penicillin?

A lucky accident

In September 1928, Fleming returned from a holiday to find that one of his dishes of Staphylococcus bacteria had been contaminated by mold. Around the mold, the bacteria had died, leaving a clear ring. Instead of throwing the dish away, he investigated and named the active substance “penicillin.”

Fleming later said: “One sometimes finds what one is not looking for.”

From discovery to medicine

1. 1928Fleming discovers penicillin’s bacteria-killing effect
2. 1929He publishes his findings but struggles to purify it
3. 1939–1941Howard Florey and Ernst Chain at Oxford purify penicillin and test it, first in mice, then in a human patient
4. 1942–1944US and British companies mass-produce it, using deep-tank fermentation
5. 1944Penicillin is widely available to Allied troops for D-Day
6. 1945Fleming, Florey and Chain share the Nobel Prize in Physiology or Medicine

A key contribution came from a moldy cantaloupe found in a market in Peoria, Illinois, in 1943. Its mold strain produced far more penicillin than Fleming’s and became the source for mass production.

Why it mattered

Before antibiotics, a scratch or sore throat could lead to a deadly infection. Penicillin, the first widely used antibiotic, made infections such as pneumonia and blood poisoning much more treatable and launched the age of modern antibiotics.

Fleming’s warning

In his Nobel lecture, Fleming warned that misusing penicillin could make bacteria resistant. Today, antibiotic resistance is a major global health concern, which is why doctors prescribe antibiotics only when needed. Antibiotics don’t work against viruses such as colds and flu.

Infections can lead to serious conditions; see what sepsis is. For another medical pioneer, read about Marie Curie.