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Penicillin: the accident that saved many lives

Fleming in his Lab - Photo. Date: 1881 - 1955
Alexander Fleming in his laboratory, 1881 – 1955


There have been many happy accidents in science. Several of these were of great benefit to medicine.

For example, in 1895, a German physicist working with a cathode ray tube happened to place his hand in front of the rays and found that he could see his bones in the image projected onto the screen. Soon after that, the first X-ray images were produced.

There have been other instances where serendipity played a role in unearthing effective treatments against diseases. 



The most famous of these happy accidents is the discovery of Penicillin as an antibiotic remedy. 

Alexander Fleming, a Scottish bacteriologist, worked at the inoculations department at St Mary’s Hospital in the early 1900s. 

In September 1928, Fleming had left a pile of bacteria cultures in his laboratory before going on holiday with his family. The cultures he was studying were known to cause septic infections. By accident, he left one of the Petri dishes uncovered.

Fleming returned to find that a bluish-green mold, similar to the mold found on bread, had contaminated the specimen. The area around the mold in the Petri dish was clear of bacteria. 

Fleming observed that the mold seemed to have killed the germs. This mold was identified as a strain of Penicillium. He saw this as a potential treatment for bacterial infections. 

Penicillin culture,1929
Penicillin culture, 1929



Fleming was able to further identify that it wasn’t just the mold that killed the bacteria but the ‘juice’ the mold seemed to produce. 

He also discovered that the ‘mold juice‘ was effective against pathogens that are responsible for diseases like Meningitis, Diphtheria and Gonorrhea. 

Fleming’s effort would bear no further fruits. He was not able to produce and purify the ‘mold juice’ in substantial quantities.

However, he named the substance Penicillin and published his findings in the British Journal of Experimental Pathology in 1929. This crucial step allowed others to build on his work.

A decade later, Fleming’s findings piqued the interest of two Oxford scientists: Howard Florey and Ernst Chain. Eventually, they found a way to mass-produce the antibiotic in a form that could kill harmful bacteria without having any toxic effects on the human body.

Vintage vials of Penicillin G
Vintage vials of Penicillin G



During World War I, Alexander Fleming was stationed in France and served in the Army Medical Corps as a captain. He observed that the death of soldiers was not always from wounds inflicted in battle, but rather from bacterial infections.

The principal treatment of such infections consisted of the administration of antiseptics. Fleming noted that these often did more harm than good. He wrote about this, however, his findings were not taken seriously at the time.

During World War I, the death rate from bacterial pneumonia was 18%. In WWII, thanks to Penicillin, the death rate from the same condition fell to less than 1%. This enabled many soldiers to return home in good health.



The mass production of Penicillin is credited with saving the lives of many thousands of soldiers during World War II. 

Antibiotics of the Penicillin family have been found to cure a wide variety of bacterial infections from mild, moderate upper respiratory tract infections to skin ulcers and urinary tract infections.

In 1944, Alexander Fleming was knighted by King George VI. In 1945, he received a Nobel Prize in Physiology or Medicine, together with Howard Florey and Ernst Boris Chain. 

The praise was well deserved, as infections that were once life-threatening are now only mild inconveniences because of Penicillin’s versatility and efficacy. Penicillin richly deserves its place as one of the most important anti-infective drugs of all time.

Interestingly, Fleming was not the first to observe the antibacterial effect of Penicillium. Between 1868 and 1873, a famous surgeon named Theodor Billroth discovered that it inhibited bacterial growth – but nothing was done about it at the time. He died when Fleming was 13 years old.

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Learn more: GIDEON Guide to Antimicrobial Agents

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