Alexander Fleming

Alexander Fleming was born on 6 August 1881 at Lochfield farm near Darvel in Ayrshire, Scotland, the third of four children of Hugh Fleming, a farmer, and Grace Stirling Morton.¹ After attending Loudoun Moor School and Darvel School, he moved to London at age 13 to live with an elder brother, where he worked as a shipping clerk before enrolling at the Royal Polytechnic Institution.² Influenced by his brother Tom, a physician, Fleming studied medicine at St Mary's Hospital Medical School, graduating with distinction in 1906.¹ He joined the research department of Almroth Wright, a pioneer in vaccine therapy, and became a lecturer at St Mary's in 1908.²

During World War I, Fleming served as a captain in the Royal Army Medical Corps and worked in battlefield hospitals in France, where he observed that antiseptics often did more harm than good by killing leukocytes. This led him to advocate for better wound hygiene and to study antibacterial substances. After the war, he returned to St Mary's and continued his research on antibacterial agents, including the enzyme lysozyme, which he discovered in 1922 in nasal mucus and tears. Lysozyme was the first natural antibiotic discovered, though it was not potent enough for therapeutic use.

In September 1928, Fleming returned to his laboratory after a holiday and noticed that a petri dish of Staphylococcus bacteria had been contaminated by a mold, and the bacteria around the mold had been destroyed. He identified the mold as Penicillium notatum and named the antibacterial substance it produced 'penicillin'. Fleming published his findings in 1929, but he was unable to purify or stabilize the compound, and the discovery did not immediately lead to clinical use. He continued to use crude penicillin to isolate certain bacteria, but it was not until the late 1930s that Howard Florey and Ernst Chain at Oxford developed methods to mass-produce and purify penicillin, leading to its use as a life-saving drug in World War II.

In 1945, Fleming, Florey, and Chain were jointly awarded the Nobel Prize in Physiology or Medicine for the discovery and development of penicillin.³ Fleming was knighted in 1944 and received numerous other honors, including the Legion of Honour and the Albert Medal. He served as principal of the University of Edinburgh from 1945 to 1947 and continued to research and advocate for the proper use of antibiotics, warning early about the risk of bacterial resistance.⁴ He died of a heart attack on 11 March 1955 at his home in London and was buried in St Paul's Cathedral.

Beyond penicillin, Fleming made several other contributions that are less well known. He was an early proponent of the use of bacteriophages as therapeutic agents, though this line of research was overshadowed by antibiotics. He also discovered that the mold's antibacterial effect was due to a specific substance, which he initially called 'mould juice'. Fleming's original petri dish is preserved at the British Museum, and the mold was later identified as a rare strain of Penicillium rubens, not P. notatum as originally thought.⁵ He was known for his modesty and once said, 'One sometimes finds what one is not looking for.' His discovery was largely accidental, but he was also a meticulous scientist who had been searching for antibacterial agents for years.

Penicillin

A group of antibiotics derived from Penicillium molds, used to treat bacterial infections.

Lysozyme

An enzyme found in tears, saliva, and mucus that breaks down bacterial cell walls.

Bacteriophage

A virus that infects and replicates within bacteria.