Who Discovered Antibiotics?

Alexander Fleming, a Scottish scientist, discovered the first antibiotic in the world.

Table of Contents

Alexander Fleming did not intend to become a scientist. Rather, he wanted to become a physician .


Fleming was born into a poor farming family in 1881. Fleming spent the early years of his life living on his mother’s farm in Ayrshire. Later, at age 13, he moved to London to live with his brother, a doctor. Inspired by his brother’s profession, he enrolled at St. Mary’s Medical School to follow his brother into the same noble profession.

Sir Alexander Fleming
Sir Alexander Fleming worked at his lab at St. Mary’s Hospital. Credit: Wikimedia Commons/Calibuon at English Wikibooks, cropped by User:AlanM1

At St. Mary’s, Fleming was a superstar who managed to bag every academic award available. Taking notice of his accomplishments, Almroth Wright, the head of the inoculation department, requested Fleming to stay behind. He wanted him to work at St. Mary’s as a researcher.

The Effect of the Great War

Fleming was born and raised in a difficult time. In Britain, all able-bodied men between the ages of 18 and 41 were required to fight in World War I. Fleming himself was posted as a captain in the medical corps. He served in Bologna, Italy. It was here, in the midst of the chaos, that he noticed something strange. He noticed most soldiers do not actually die from combat wounds. Rather he concluded that it was bad infections.

Penicillin Poster
By the time World War II happened, penicillin was established as an effective antibiotic and helped save millions of soldiers’ lives. Credit: Wikimedia Commons

He observed that most of the time, these infections could not be treated or controlled. On the battlefront, the go-to treatment for infections like these was antiseptics. However, most of the time these medicines would do more harm than good. After fighting in the war, Fleming returned to St. Mary’s Hospital as a professor to continue his research.

A Messy Scientist

After he returned to St. Mary’s, Fleming had but one goal in his mind. He wanted to understand why none of the medicines they had could work on the flu virus. His work was largely influenced by the conditions of the time. It was 1928 and nothing seemed to help stop the spread of the flu. The flu was killing millions at the time.

Although academically gifted, Fleming was extremely careless, especially in the lab. He had a bit of a reputation as a messy scientist. He would often leave his cultures  out in the open.

Petri Dishes
Fleming cultured his bacteria in Petri dishes like these and left them uncovered. Credit: Wikimedia Commons/Archives nationales (France)

It was this same tendency that yielded one of the most significant discoveries of the 20th century. In 1928, he took a holiday for the summer. He traded his lab settings for the beautiful hills of Scotland. However, before he left, he forgot to cover his bacterial cultures. To make matters worse, he left his Petri dishes right next to an open window!


When he returned, he noticed that his uncovered cultures were ruined. The cultures of bacteria that he’d left out had been overtaken by fungal  spores.

An Unlikely Discovery

Although disappointed, Fleming noticed something. Before he left for holiday, Fleming had cultured a specific type of bacteria, namely common staphylococcal bacteria. These spherical bacteria can cause skin and tissue infections, like boils. It can even contribute to more dangerous ailments, like pneumonia. Fleming was studying these bacteria to try and understand variations in its natural growth.

The long brush-like outgrowth is the Penicillium mold, as seen under a microscope. Credit: Wikimedia Commons/Ajay Kumar Chaurasiya.

Fleming noticed that the mold that ruined his cultures was doing something strange. Not only had it ruined his cultures with ease, but it was also killing the bacteria!


The mold was able to kill any bacteria that was in direct or close contact with the mold colonies. Fleming was amazed. He quickly isolated a bit of the mold.

Mold Juice: A Nobel Discovery

Fleming identified the isolated bit of mold as a member of the Penicillium genus, a type of fungus. He tested the fungus against multiple types of infectious bacteria. He was amazed by his findings. This mold was effective against bacteria that could cause multiple diseases. From pneumonia to meningitis, the fungus could fight them all!


Fleming later wrote his findings down. He concluded that the fungus contained some type of special “juice” that helped it kill bacteria. He named this mold juice Penicillin, after the fungus he had isolated it from.


Fleming published his discoveries in the British Journal of Experimental Pathology in 1929. However, he gained little to no recognition at the time. In fact, it wasn’t until almost 20 years later, when he was close to retirement in 1940, that other scientists began to notice his achievements.


In 1940, two scientists at the University of Oxford popularized penicillin again. Howard Florey and Ernst Chain, a pharmacologist and a biochemist respectively, were interested in mass-producing penicillin. They wanted to test just how effective it could be as a “life-saving drug.”


Florey, in particular, injected penicillin into mice with infections to test if it could counteract the infections.

Today, many more antibiotics like Azithromycin are available in pharmacies all over the world. Credit: Wikimedia Commons

In 1941, penicillin was administered to a man suffering from infection. The man was a police officer from England who was given the penicillin that the team at Oxford made. Surely enough, the man made a complete recovery and was cleared of his infections!


This marked a significant moment in history. It was the first time that Penicillin had been used on a human. Furthermore, it was also the first known use of antibiotics in human medicine.


Fleming, Florey, and Chain were all finally honored for their work in 1945. They all won the Nobel Prize in Physiology or Medicine.

Readability: 61.1


Flesch Kincaid Grade Level: 7.6.


Antibiotic: A medicine that can kill dangerous micro-organisms in our bodies.


Physician: Doctors are also known as physicians.


Culture: The growth of any living organisms, such as yeast, in a lab or controlled setting.


Bacteria: A group of single-celled micro-organisms that do not have well-organized nuclei and can cause diseases.


Fungus: A group of organisms that reproduce by making spores, that contains mushrooms and molds.

Yong Tan, Siang, MD. Alexander Fleming: Discoverer of Penicillin. July, 2015. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520913/


American Chemical Society International Historic Chemical Landmarks. Discovery and Development of Penicillin. March 23, 2023. http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/flemingpenicillin.html


Sir Alexander Fleming – Biographical. NobelPrize.org. Nobel Prize Outreach AB 2023. 23 Mar 2023. https://www.nobelprize.org/prizes/medicine/1945/fleming/biographical/


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