Who was Alexander Fleming?

When World War I broke out, Fleming, Leonard Colebrook, and Sir Almroth Wright effectively relocated the Inoculation Department of St Mary's to a British military hospital at Boulogne-sur-Mer. Fleming had been a private in the London Scottish Regiment since 1900 and was commissioned a lieutenant in 1914, later promoted to captain. Working in battlefield hospitals on the Western Front, he witnessed soldiers dying not from their wounds alone but from the sepsis that followed. The antiseptics being applied to infected wounds were, he observed, making things worse rather than better.

In a 1917 article in The Lancet, Fleming explained the problem through an experiment he was able to design partly because of his own glassblowing skills. Deep wounds created conditions where anaerobic bacteria were sheltered from any antiseptic applied to the surface. Worse, the antiseptics destroyed beneficial agents the body itself was producing to fight infection, while leaving unreachable bacteria untouched. Despite Wright's support for these findings, most army physicians continued applying antiseptics throughout the war. The experience sharpened Fleming's conviction that the body's own defences, and any substances that worked alongside them, mattered far more than the chemical agents then in use.

In late 1921, while tending bacterial culture plates at St Mary's, Fleming found that nasal mucus he had added to a contaminated plate inhibited bacterial growth, producing a clear ring around the mucus indicating that bacteria had been killed. He extended the investigation using tears collected from colleagues and co-workers, and tested sputum, blood, egg white, and other substances, finding the same bactericidal agent across all of them. He named the substance lysozyme and reported his discovery to the Medical Research Club in December 1921 and to the Royal Society the following year. On both occasions the audience responded with near-total silence.

Fleming published his findings in the Proceedings of the Royal Society B in May 1922 under the title 'On a remarkable bacteriolytic element found in tissues and secretions.' He also identified the bacterium present in the nasal mucus, naming it Micrococcus lysodeikticus, a species later reassigned as Micrococcus luteus in 1972. Although egg whites yielded larger amounts of lysozyme, the enzyme proved effective only against small counts of harmless bacteria, limiting its direct therapeutic use. The broader significance of lysozyme as part of the body's innate immune defences was not recognised until near the end of the twentieth century. The patient described in the original publication as suffering from acute coryza was, as Fleming's research notebook confirms, Fleming himself.

On 3 September 1928, Fleming returned to his laboratory at St Mary's after a family holiday in Suffolk. Before leaving he had inoculated staphylococci on culture plates and left them on a bench. One plate had become contaminated with a fungus, and the colonies of staphylococci immediately surrounding it had been destroyed. Colonies farther away remained intact. Fleming remarked, 'That's funny,' and showed the plate to his former assistant Merlin Pryce, who noted the similarity to the lysozyme discovery. Fleming identified the mould as belonging to the genus Penicillium, and on 7 March 1929 gave the name penicillin to the antibacterial substance it produced. The mould was eventually classified as Penicillium rubens.

Fleming grew the mould in pure culture and tested the broth against a wide range of organisms. He found it effective against staphylococci and many other Gram-positive pathogens responsible for diseases including scarlet fever, pneumonia, meningitis, and diphtheria. It also affected Neisseria gonorrhoeae despite that bacterium being Gram-negative. He presented his findings to the Medical Research Club on 13 February 1929 and published them in the British Journal of Experimental Pathology, but neither audience nor readership showed significant interest. Producing penicillin in large amounts and isolating its active compound proved chemically difficult, and even with assistance from biochemists at the London School of Hygiene and Tropical Medicine, purification remained out of reach. As a result, penicillin attracted little attention through most of the 1930s.

It was the Oxford team of Howard Florey and Ernst Chain, working at the Sir William Dunn School of Pathology, who finally purified penicillin into a stable form in 1940 and developed methods for mass production by 1945. Fleming himself kept, grew, and distributed the original mould for twelve years and continued seeking chemists with the skill to isolate it. When Chain learned that Fleming was travelling to Oxford to see the work, he reportedly said, 'Good God! I thought he was dead.' Fleming was modest about his role, calling his fame the 'Fleming Myth' and crediting Florey and Chain with transforming a laboratory curiosity into a practical drug. Sir Henry Harris later summarised the chain of dependency: without Fleming, no Chain; without Chain, no Florey; without Florey, no Heatley; without Heatley, no penicillin.

Fleming shared the 1945 Nobel Prize in Physiology or Medicine with Howard Florey and Ernst Chain for the discovery of penicillin and its curative effect in infectious diseases. He had been knighted the previous year, in 1944, for his scientific achievements. In 1999 Time magazine named him one of the 100 Most Important People of the 20th century, and in 2002 the BBC included him in its poll of the 100 Greatest Britons.

Even before the drug reached widespread clinical use, Fleming had identified the risk of antibiotic resistance. He observed that bacteria developed resistance when penicillin was used in doses too small or for periods too short to eliminate them entirely. On 26 June 1945 he stated publicly that a person who underused penicillin and thereby bred resistant organisms was morally responsible for the deaths those organisms subsequently caused. In his Nobel Lecture he warned that if penicillin could be bought freely in shops, the ignorant user might underdose and make microbes resistant. Experiments as early as 1942 had already demonstrated that Staphylococcus aureus could develop resistance under prolonged low-level exposure, and around the same time the first clinical case of penicillin resistance was reported.

Fleming married Sarah Marion McElroy on 24 December 1915; their son Robert became a general medical practitioner. After Sarah's death in 1949, Fleming married Amalia Koutsouri-Vourekas, a Greek colleague at St Mary's, in 1953. He died of a heart attack at his London home on 11 March 1955, and his ashes are buried in St Paul's Cathedral. The laboratory where he discovered penicillin survives as the Alexander Fleming Laboratory Museum at St Mary's Hospital in Paddington.