Alexander Fleming (6 August 1881–11 March 1955) was a Scottish physician and bacteriologist best known for discovering the antibacterial activity of penicillin in 1928. His research also identified lysozyme, an antibacterial substance found in bodily tissues and secretions. He shared the 1945 Nobel Prize in Physiology or Medicine with Ernst Boris Chain and Howard Walter Florey for the discovery of penicillin and its curative effects in infectious diseases. Fleming’s initial observations were distinct from the subsequent purification, clinical development, and industrial production that made penicillin widely available. (nobelprize.org)
Early life and medical training
Fleming was born at Lochfield Farm near Darvel in Ayrshire, Scotland, to Hugh Fleming and Grace Morton. He attended local schools and Kilmarnock Academy before continuing his education in London. After four years working in a shipping office, he entered St Mary’s Hospital Medical School in 1901 and qualified in 1906. He subsequently obtained the University of London’s MB, BS degrees with a gold medal in 1908. (nobelprize.org)
On qualifying, Fleming joined the research department at St Mary’s as an assistant bacteriologist to Almroth Wright, whose work included vaccine therapy. This association established the institutional setting for most of Fleming’s career. His research combined laboratory investigation with problems arising in clinical medicine, particularly the behavior of bacteria and the measurement of antibacterial activity. He became professor of bacteriology in 1928 and emeritus professor in 1948. (nobelprize.org)
Wartime research and antibacterial substances
During World War I, Fleming served in the Royal Army Medical Corps and worked with Wright’s research team at Boulogne in France. They investigated infected war wounds, including the organisms present and the limitations of contemporary treatments. Fleming contributed studies of streptococcal infection and gas gangrene, as well as experimental investigations supporting Wright’s objections to indiscriminate reliance on chemical antiseptics in wounds. (history.rcp.ac.uk)
After returning to St Mary’s in 1918, he continued examining antibacterial substances that would not be toxic to animal tissues. His work also involved developing assays for measuring antibacterial activity in blood and other body fluids. Such methods later became useful in his investigations of penicillin. These interests connected his wartime research with his subsequent studies of naturally occurring antibacterial agents. (nobelprize.org)
Discovery of lysozyme
Fleming first observed the substance he named lysozyme in 1921 and published his findings in 1922. His investigations began with nasal secretions and showed that a component of these secretions could rapidly dissolve certain bacteria. He subsequently investigated its occurrence in other biological materials, establishing that antibacterial activity was not confined to a single sample or secretion. (nobelprize.org)
Lysozyme is an enzyme—a protein that catalyzes a chemical reaction. It breaks bonds in peptidoglycan, a structural component of bacterial cell walls. Damage to this layer can cause susceptible bacteria to rupture. Lysozyme occurs in tears, saliva, mucus, and other bodily fluids. Fleming’s discovery therefore concerned a naturally occurring antibacterial substance rather than an externally administered chemical disinfectant. (ebi.ac.uk)
Discovery of penicillin
In September 1928, while studying staphylococcal cultures at St Mary’s, Fleming noticed that a contaminating mold colony was surrounded by altered bacterial colonies. Near the mold, the staphylococci had become transparent and were undergoing dissolution. Rather than simply discarding the contaminated culture, he investigated the effect experimentally. He named the active substance penicillin after the mold’s genus, Penicillium. (history.rcp.ac.uk)
Fleming found that liquid in which the mold had grown inhibited susceptible bacteria even when substantially diluted. His 1929 paper described important properties of the substance. Later, in his Nobel lecture, he distinguished its ability to inhibit bacterial growth, kill bacteria, and produce bacterial dissolution. He also described its movement through agar, an experimentally useful property for demonstrating antibacterial activity around a sample. (nobelprize.org)
Nevertheless, the original discovery did not immediately yield a practical medicine. Fleming and his colleagues attempted to concentrate penicillin, but their procedures did not produce a sufficiently usable preparation. Recognizing antibacterial activity and obtaining a stable therapeutic product were separate experimental problems. (history.rcp.ac.uk)
Clinical development and industrial production
At the University of Oxford, Florey, Chain, Norman Heatley, and colleagues developed techniques for extracting and preparing penicillin and advanced it into clinical treatment in 1941. This work established its therapeutic potential beyond Fleming’s original laboratory observations. (acs.org)
Large-scale production required further improvements during World War II. British and American researchers, government laboratories, and pharmaceutical manufacturers collaborated on production methods. Changes to nutrient media, selection of more productive mold strains, and submerged fermentation increased yields. These developments made it possible to manufacture quantities far exceeding those available in the early clinical investigations. The history of penicillin therefore encompasses Fleming’s discovery, the Oxford team’s clinical development, and subsequent industrial work. (acs.org)
Recognition and later life
Fleming became a fellow of the Royal Society in 1943 and was knighted in 1944. The following year, he, Chain, and Florey each received one-third of the Nobel Prize in Physiology or Medicine. In his 1945 Nobel lecture, Fleming warned that exposing bacteria to nonlethal amounts of penicillin could select resistant organisms, explicitly identifying the problem now termed antibiotic resistance. (nobelprize.org)
He served as rector of the University of Edinburgh from 1951 to 1954. His first wife, Sarah Marion McElroy, whom he married in 1915, died in 1949; their son Robert became a physician. In 1953 he married Amalia Voureka, a medically qualified Greek colleague. Fleming died in London on 11 March 1955, and his ashes were interred in St Paul’s Cathedral. (nobelprize.org)