Alexander Fleming and the Discovery of Penicillin


Pharmacy Times takes a look back into the 1920s, when the group of antibiotics was discovered.

The discovery of penicillin, which has saved millions of lives, was made by physician/scientist Alexander Fleming.

Born in Scotland in 1881, he eventually moved to London with his family. After completing school, Fleming 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 from St. Mary’s Medical School at London University.

While serving in the army, he became a marksman. The captain convinced Fleming to pursue a career in research instead of surgery, so that he could stay at the school. Fleming was taken under the wing of Sir Almroth Wright, a pioneer in immunology and vaccine research. 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 as a result of uncontrolled infection. 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 on.

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 non-harmful bacteria.

In 1928, he started to research common staphylococcal bacteria. An uncovered Petri dish near an open window became contaminated with mold. 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. Gram-positive pathogens cause diseases, such as diphtheria, gonorrhea, meningitis, pneumonia, and scarlet fever. Fleming discovered that it was not the mold itself but 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 Chain and Howard Florey, became interested in penicillin. Soon, they were able to mass produce penicillin for use during World War II.

Fleming received many awards, including 30 honorary degrees, and most notably, the Nobel Prize in Physiology/Medicine in 1945. He was also named one of the most important people of the 20th century by Time Magazine.

In terms of his personal life, Fleming was known as modest, patient, quiet, shy, and unemotional. He avoided attention and was even 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 she passed away 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, Fleming married Dr. Amalia Koutsouri-Vourekas in a Greek church in London.

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

It was said that Fleming “died as he wished: quietly, without a gradual decline in physical or mental capacity, and even without inconveniencing his physician.”


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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