Alexander Fleming Discovers Penicillin

Pharmacy TimesAugust 2020
Volume 88
Issue 8

Before the bacteria killer’s introduction, there were no effective treatments for infections.

Physician and scientist Alexander Fleming discovered penicillin, which has saved millions of lives since 1928.

Born in Ayrshire, Scotland, in 1881, he eventually moved to London, England, with some of his siblings. After completing school, he worked in a shipping office for several years before starting medical school, using money from his share of his uncle’s estate to pay for his education. In 1906, Fleming graduated with distinction from St Mary’s Medical School at London University.

During his service in the Territorial Army, 1901- 1914, Fleming became a skilled marksman. The captain of St. Mary’s rifle club, eager to have Fleming join, convinced him to pursue a career in research instead of surgery, which would have entailed his leaving the school. He introduced him to Sir Almroth Wright, a pioneer in immunology and vaccine research, and member of the rifle club, who took Fleming under his wing. Fleming remained with this research group for his entire career.

As an Army Medical Corps captain in World War I, he witnessed many of his fellow soldiers die because of uncontrolled infection from their wounds. At the time, antiseptics were used and often caused more harm than good. Fleming wrote an article discussing the anaerobic bacteria present in deep wounds, which were not destroyed by the antiseptics. His research was not accepted initially, but he continued his work.

In 1922, Fleming discovered lysozyme, an enzyme with weak antibacterial properties that inhibited bacterial growth. He also found lysozyme in fingernails, hair, saliva, skin, and tears. In his research, Fleming found that lysozyme was effective against only a small number of nonharmful bacteria.

In 1928, he started to research common staphylococcal bacteria. An uncovered Petri dish near an open window had become contaminated with mold during his absence. Fleming realized that the bacteria near the mold were dying. He isolated the mold and identified it as Penicillium genus, which he found to be effective against all Gram-positive pathogens. Pathogens cause diseases such as diphtheria, gonorrhea, meningitis, pneumonia, and scarlet fever. Fleming discovered that it was not the mold itself but rather a “juice” it had produced that had destroyed the bacteria. He named this “mold juice” penicillin.

Later, Fleming said: “When I woke up just after dawn on September 28, 1928, I certainly didn’t plan to revolutionize all medicine by discovering the world’s first antibiotic, or bacteria killer. But I suppose that was exactly what I did.”

Initially, the medical community was not so enthusiastic about Fleming’s penicillin discovery. He also had difficulty isolating large quantities of “mold juice.” In 1940, just as Fleming was about to retire, 2 fellow scientists, Ernst Boris Chain and Howard Walter Florey, became interested in penicillin. Soon, they were able to mass produce it for use during World War II.

Fleming received many awards, including 30 honorary degrees and, most notably, the Nobel Prize in Physiology or Medicine, with Chain and Florey, in 1945. Time magazine also named him one of the most important people of the 20th century.

In his personal life, Fleming was modest, patient, quiet, shy, and unemotional. He avoided attention and was sometimes painfully silent around close friends and even his wife, Sarah Marion McElroy, a nurse. Fleming and his wife had a son, Robert, who became a general practitioner. When Sarah died after 34 years of marriage, Fleming had a very difficult time. He lost himself in his work, spending most of his time behind closed doors in the lab. In 1953, however, Fleming married his colleague Amalia Koutsouri-Vourekas, MD, in a Greek church in London.

He died at home, suddenly, of coronary thrombosis, in 1955, after suffering from stomach upset for weeks.


Tan SY, Tatsumara Y. Alexander Fleming (1881-1955): discoverer of penicillin. Singapore Med J. 2015;56(7):366-367. doi:10.11622/ smedj.2015105

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