Alexander Fleming

Sir Alexander Fleming was a Scottish physician and microbiologist whose pioneering discoveries reshaped modern medicine. Best known for identifying penicillin in 1928, he introduced the world to the first widely effective antibiotic, a breakthrough often described as one of the greatest achievements in the fight against infectious disease. His scientific contributions also included the discovery of lysozyme in 1922, an enzyme involved in natural immunity. Fleming’s career encompassed clinical service, research innovation, and public recognition, culminating in the award of the Nobel Prize in Physiology or Medicine in 1945 alongside Howard Florey and Ernst Chain. Celebrated as one of the most influential figures of the twentieth century, his legacy continues to define the foundations of antimicrobial therapy.

Early Life and Education

Alexander Fleming was born on 6 August 1881 at Lochfield farm near Darvel in Ayrshire, Scotland. He was the third of four children born to Hugh Fleming and Grace Stirling Morton, although his father also had four surviving children from a previous marriage. Hugh Fleming died when Alexander was seven, leaving the family to depend on the agricultural livelihood of Lochfield.
Fleming attended Loudoun Moor School and later Darvel School, showing academic promise that earned him a two-year scholarship to Kilmarnock Academy. After this period he moved to London, enrolling at the Royal Polytechnic Institution. His early working life included four years in a shipping office, a phase brought to an end when an inheritance enabled him to pursue medical studies. Encouraged by his brother Tom, who was already a practising physician, Fleming entered St Mary’s Hospital Medical School in Paddington in 1903. He qualified with distinction in 1906, earning an MBBS degree.
During his student years he served as a private in the London Scottish Regiment and was an active member of the medical school’s rifle club. His skill as a marksman helped influence his career path: the club’s captain encouraged him to join the research department at St Mary’s to ensure he remained associated with the unit. Under the mentorship of Sir Almroth Wright, a leading figure in immunology and vaccine research, Fleming flourished. In 1908 he gained a BSc in bacteriology with a gold medal and began lecturing at St Mary’s, a position he retained until the First World War.

Military Service and Early Scientific Work

Fleming was commissioned as a lieutenant in the Royal Army Medical Corps at the outbreak of the First World War and was later promoted to captain. He served in hospitals at the Western Front, where the high mortality from infected wounds profoundly influenced his scientific direction. He observed that antiseptics used to treat war injuries often worsened deep infections by eliminating useful defensive substances in the tissues without effectively reaching bacteria shielded within the wounds.
In 1917 Fleming published his findings in The Lancet, demonstrating through meticulous experimentation—facilitated by his own glassblowing skills—that antiseptics could be more harmful than beneficial when used on severe lacerations. Although Wright strongly supported these conclusions, many military doctors continued using traditional antiseptics throughout the conflict. Nevertheless, Fleming’s observations contributed significantly to evolving medical understanding of wound management.
After the war he returned to St Mary’s Hospital, where he pursued research and was later appointed Professor of Bacteriology in 1928. He also served as Rector of the University of Edinburgh for a three-year term beginning in 1951.

The Discovery of Lysozyme

In 1921 Fleming made an unexpected discovery that revealed the presence of natural antibacterial substances in bodily secretions. While examining contaminated culture plates, he observed that nasal mucus caused certain bacteria to dissolve, producing a distinct zone of inhibition. His subsequent experiments showed that this effect was rapid, reproducible, and present in multiple human secretions, including tears, saliva, sputum, and blood.
Fleming introduced the term lysozyme in 1922 to describe the enzyme responsible for this bacteriolytic activity. His work demonstrated that lysozyme was highly effective against Micrococcus lysodeikticus, a species he identified and named himself, which later became recognised as Micrococcus luteus. Although lysozyme acted mainly on non-pathogenic bacteria and thus had limited therapeutic application, Fleming recognised its significance to natural immunity. At the time, the scientific community paid little attention, but his persistent interest in the enzyme shaped subsequent immunological research. Only decades later was the broader importance of lysozyme fully appreciated.

The Discovery of Penicillin

Fleming’s most famous discovery occurred in 1928. Returning from holiday, he observed that a mould contaminating one of his staphylococcal culture plates had killed the surrounding bacterial colonies. Investigating further, he isolated the active substance produced by the mould Penicillium rubens, identifying it as a potent antibacterial agent. He named the compound penicillin.
Penicillin showed remarkable effectiveness against a wide range of bacteria responsible for severe human infections, including streptococci, staphylococci, and pneumococci. Fleming published his findings in 1929, emphasising the compound’s therapeutic potential and unusually low toxicity. However, despite the significance of the discovery, penicillin initially received little immediate development due to the difficulty of isolating and producing it in pure form.
The true transformative impact of penicillin emerged a decade later, when Howard Florey, Ernst Chain, and their research team at Oxford succeeded in extracting and mass-producing the compound. Their work demonstrated penicillin’s unparalleled value in treating systemic bacterial infections and paved the way for widespread clinical use during the Second World War.
In recognition of their collective achievement, Fleming, Florey, and Chain were jointly awarded the Nobel Prize in Physiology or Medicine in 1945. In his Nobel lecture, Fleming remarked that lysozyme—not penicillin—had been his first antibiotic discovery, reflecting his lifelong interest in bacteriolytic substances.

Recognition and Later Career

Fleming’s contributions brought him global acclaim. He was knighted in 1944 and became a widely celebrated scientific figure following the dramatic wartime success of penicillin. Numerous honours followed, including election to prestigious academic societies and widespread public admiration. In 1999 he was listed in Time magazine’s compilation of the 100 most important people of the twentieth century. The BBC named him among the 100 Greatest Britons in 2002, and an opinion poll in 2009 placed him among the greatest Scots of all time.
Despite the recognition, Fleming remained modest regarding his achievements, stressing the role of chance in scientific discovery and the importance of collaborative research.

Scientific Legacy

Sir Alexander Fleming’s work revolutionised medicine. Penicillin opened the modern era of antibiotic therapy, drastically reducing mortality from infections that had previously been life-threatening and laying the foundation for subsequent antibiotic development. Lysozyme, though initially overlooked, became an important model for understanding innate immunity. His insights into antiseptic misuse during wartime influenced medical practice and contributed to better wound-treatment protocols.