Alexander Fleming and the Discovery of Penicillin

Scottish medicine · Observation, development and teamwork

In September 1928, Alexander Fleming noticed that a stray mould on a dish of bacteria had left a clear space around itself. It was a small observation in a London laboratory, but the work that followed would change the treatment of bacterial infections. Fleming was born in Ayrshire; the medicine eventually known as penicillin depended on his experiments and on a second team's years of work to make the substance usable.

From an Ayrshire farm to St Mary’s Hospital

Fleming was born in 1881 at Lochfield, near Darvel, one of eight surviving children in a farming family. He moved to London as a teenager and, after a period of study and work, won a scholarship to St Mary’s Hospital Medical School in 1901. The hospital became his professional base. In 1906 he joined its Inoculation Department under bacteriologist Almroth Wright.

During the First World War, Fleming worked in a wound-research laboratory in France. He investigated the chemical antiseptics then used on injured soldiers and found that some could damage the white blood cells needed to fight infection without reliably reaching bacteria deep in a wound. That experience helps explain his lasting interest in how the body and antibacterial substances work together.

The work before the famous dish

Fleming had already learned to follow an unexpected laboratory result. In 1921 he identified lysozyme after noticing that a substance in nasal mucus could break down certain bacteria. He and a colleague subsequently found it in tears, saliva and other body fluids. Lysozyme proved much less useful against many disease-causing bacteria, yet the investigation showed his willingness to test an odd observation rather than dismiss it.

In 1928 he was studying staphylococci, bacteria that can cause boils and serious infections. A culture dish was left out rather than placed in an incubator while he was away. A Penicillium mould grew on it. Around the colony the staphylococci were absent or damaged. The exact sequence is less tidy than the familiar “eureka” tale: Fleming’s notes are sparse, and his later descriptions differed over whether his first observation was bacterial destruction or inhibited growth.

What Fleming established in 1928 and 1929

He did more than point to a contaminated plate. Fleming tested the mould’s effect on different microbes, found that only certain Penicillium strains produced the antibacterial substance, and called that substance penicillin. He explored how the crude material could be made and how its activity held up under different conditions. His findings appeared in a 1929 paper.

September 28 is often given as the day of the discovery, but the surviving record more securely places the work in September 1928. The date is a useful anniversary, not a reason to compress the research into a single moment.

Why the discovery was not yet a medicine

Fleming could not isolate and produce enough stable penicillin for a course of treatment. He considered uses such as treating surface infections and separating bacteria in laboratory cultures. His paper attracted limited attention in the following decade. A clear zone on a dish showed antibacterial potential; it did not solve the problems of purification, dosage, testing and production.

At the University of Oxford, Howard Florey, Ernst Chain, Norman Heatley and their colleagues took up that challenge. They developed ways to grow the mould, measure penicillin’s activity and concentrate it. Animal tests in 1940 were promising. On 12 February 1941, police officer Albert Alexander received experimental penicillin treatment at Oxford’s Radcliffe Infirmary. He initially improved, but the team ran out of the scarce drug and he died. His case showed both the promise of penicillin and the urgent need to make far more of it.

Florey and Heatley sought industrial help in the United States in 1941. Larger-scale production during the war moved penicillin from laboratory work toward wider clinical use. Fleming, Florey and Chain shared the 1945 Nobel Prize in Physiology or Medicine; Heatley’s technical contribution is an essential part of the fuller story.

A discovery with a lasting lesson

Penicillin opened a new era of treatment for many bacterial infections. Fleming also warned in his 1945 Nobel lecture that exposing bacteria to too little penicillin could encourage resistance. The history is therefore about careful observation, collaborative development and responsible use, not just a fortunate accident in one dish.

Explore other ideas in our guide to Scottish inventions that changed the world. To browse a gift bearing your own family name, see our Scottish gifts and select the spelling your family uses.

For another chapter in the history of patient care, read James Young Simpson’s work on anaesthesia. Pain relief and treatment of infection solved different problems, and neither should be confused with the other.

Sources and further reading

• Science History Institute, Alexander Fleming biography and 1928 experiments
• University of Oxford, Norman Heatley and the first patient
• Oxford History of Science Museum, penicillin culture and clinical development
• Alexander Fleming’s 1945 Nobel lecture
• German Patent and Trade Mark Office, September 28 anniversary account