Discovery of Penicillin

How Mold Revolutionized Medicine

Did you know that the first effective medication against bacterial infections was actually discovered by accident and is now one of the most widely used antibiotics in the world?

The discovery and development of penicillin ushered in an era of antibacterial treatment that fundamentally changed medicine. Before penicillin, doctors struggled to treat life-threatening bacterial infections such as infective endocarditis, rheumatic fever, pneumonia, gonorrhea, and syphilis.

Today, people worldwide often take for granted the effectiveness of modern antibiotics, which not only helped eradicate certain diseases but also led to an average eight-year increase in human lifespan.

Alexander Fleming, pictured in his laboratory, 1943

Alexander Fleming, pictured in his laboratory, 1943

In 1928, professor of bacteriology at St. Mary’s Hospital in London, Alexander Fleming, returned to his laboratory from a summer vacation and noticed a growth that had developed in one of the petri dishes he was using to culture the Staphylococcus bacteria. The dish had been accidently left open, and Fleming observed it was contaminated by mold, which appeared to have produced a bacteria-free ring around itself.

Fleming concluded that the mold had inhibited the bacteria’s development by releasing a substance that had caused the bacterial cells to undergo lysis—a medical term that refers to the breaking down of a cell’s membrane.

One sometimes finds what one is not looking for.

Alexander Fleming

Following further analysis, Fleming determined that the active substance released from the mold not only destroyed Staphylococcus bacteria but was also effective against a wide range of harmful microorganisms, such as those that cause meningitis and diphtheria. Fleming observed that the active substance was a type of Penicillium mold and named it penicillin.

Chemical structure of the Penicillin core

Chemical structure of the Penicillin core

The professor established that the Penicillium mold was capable of killing bacteria harmful to humans and that it was suitable to use as an antibiotic against bacterial infection. However, Fleming’s attempts to isolate pure penicillin from the mold ended in failure.

In June 1929, Fleming published his findings in the British Journal of Experimental Pathology, but the potential therapeutic benefits of penicillin were not fully appreciated by the medical community at the time.

Fleming continued to show an interest in the development of penicillin, but because of the difficulties associated with isolating the antibiotic agent, he turned his attention to other areas of bacteriology.

It wasn’t until 1939, a decade later, that Fleming’s findings were taken to the next stage of development, when Oxford University researchers Howard Florey and Ernst Chain successfully extracted the active ingredient from Penicillium mold and scientifically proved that penicillin could be used to cure bacterial infections in mice.

A poster attached to a curbside mailbox offering advice to World War II servicemen: Penicillin cures gonorrhea in 4 hours, 1944

A poster attached to a curbside mailbox offering advice to World War II servicemen: Penicillin cures gonorrhea in 4 hours, 1944

By 1940, researchers had developed a method for mass-producing penicillin, prompting Howard Florey to travel to the United States to collaborate with pharmaceutical companies on scaling up production. Despite challenges in increasing penicillin yields, U.S. laboratories refined the production process, ensuring that the antibiotic was ready for large-scale production by March 1944. This timely production made penicillin available to treat wounded British and American soldiers during the D-Day landings in Normandy in June 1944, during World War II.

Today, the antibiotic and its derivatives continue to be used around the world to treat a wide range of infections. Without antibiotics, global life expectancy would drop to around 50 years, and infectious diseases would again become leading causes of death worldwide. However, the misuse and overuse of antibiotics have led to the emergence of antibiotic resistance, posing a significant threat to public health across the globe. This situation underscores the critical importance of using antibiotics responsibly to preserve their effectiveness and continue benefiting from their life-saving properties.

Words of wisdom

“He who is not satisfied with a little is satisfied with nothing.” —Epicurus

“We don’t even ask happiness, just a little less pain.” —Charles Bukowski

“The things you think about determine the quality of your mind.” —Marcus Aurelius

“If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is.” —John von Neumann


How did you like the episode?

Login or Subscribe to participate in polls.