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How Penicillin Was Discovered: The Story of a Lucky Accident

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This is a true story from the history of science, retold in simple language.

Some of the world’s most important discoveries began with a mistake. One of the most famous is the discovery of penicillin, the first widely used antibiotic. It started with an untidy laboratory, a summer holiday and a scientist curious enough to look twice.

A messy bench in London

In 1928, Alexander Fleming was a Scottish doctor and bacteriologist working at St Mary’s Hospital in London. He studied Staphylococcus, bacteria that can cause boils, sore throats and serious infections. Fleming was a talented researcher, but he was not known for keeping a tidy workbench.

Before leaving for a summer holiday, he stacked several glass dishes of bacteria on his bench instead of cleaning them.

The mould that should not have been there

When Fleming returned in September 1928, he began sorting through the old dishes. On one of them, he noticed something strange. A patch of mould had grown on the dish, probably from spores that drifted in through the air. Around the mould, there was a clear ring where the bacteria had disappeared.

Many people would have thrown the dish away. Fleming did not. He realised the mould seemed to be producing a substance that killed bacteria. The mould belonged to the Penicillium group, so he called the substance penicillin.

A discovery that almost faded away

Fleming published his findings in 1929. He showed that penicillin could kill many harmful bacteria. However, he struggled to produce it in large amounts and to purify it into a stable medicine. For about ten years, penicillin remained more of a laboratory curiosity than a cure.

The Oxford team brings it to life

The story continued at the University of Oxford. Around 1939, a team led by Howard Florey and Ernst Chain, with the help of Norman Heatley and others, took up Fleming’s work. They developed ways to grow the mould, extract penicillin and purify it.

Their experiments on mice in 1940 showed that penicillin could protect animals from deadly infections. In 1941, the team treated a patient for the first time. The early results were encouraging, but they faced a painful problem: there was far too little penicillin to go around.

From a laboratory to the world

During the Second World War, the need for a medicine to treat infected wounds was enormous. Scientists and companies, particularly in the United States, worked to grow penicillin on a large scale. They found better strains of mould and better ways to grow them in huge tanks. By the end of the war, penicillin was being produced in large quantities and was saving many lives.

In 1945, Alexander Fleming, Howard Florey and Ernst Chain shared the Nobel Prize in Physiology or Medicine for the discovery of penicillin and its use in treating infections.

A warning that still matters

Fleming also warned that bacteria could become resistant to penicillin if the medicine was misused, for example by taking too little or stopping treatment too early. Today, antibiotic resistance is a serious global health problem, which makes his warning even more important.

Lessons from the story

  • Curiosity matters. Fleming’s discovery came from asking “why?” when he saw something unusual.
  • Discoveries need teamwork. Fleming found penicillin, but the Oxford team and many others turned it into a medicine.
  • Persistence pays off. Penicillin took more than a decade to move from a dish to patients.
  • Use medicines responsibly. Take antibiotics only when prescribed and complete the course as your doctor advises.

Quick facts

  • Discovered by: Alexander Fleming
  • Year: 1928, at St Mary’s Hospital, London
  • Developed as a medicine by: Howard Florey, Ernst Chain and their team at Oxford
  • Nobel Prize: 1945, shared by Fleming, Florey and Chain

Enjoy stories with a lesson? Read The Cracked Pot, the story of the Karakoram Highway, and The Boy Who Counted the Stairs.

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