When Alexander Fleming discovered Penicillin by accident


Fleming was born on August 6, 1881 at his parents’ farm located near the small town of Darvel, in Scotland, UK.

His parents, Hugh Fleming and Grace Stirling Morton, were both from farming families. His father’s health was fragile; he died when Alexander was just seven years old.

Alexander’s earliest schooling, between the ages of five and eight, was at a tiny moorland school where 12 pupils of all ages were taught in a single classroom.


Darvel School was Alexander’s next school, which involved an eight-mile round trip on foot every school-day. At the age of 11 his academic potential was recognized and he was awarded a scholarship to Kilmarnock Academy, where he boarded for about two years before leaving for London.

Alexander arrived in London early in 1895, age 13. This was the year his fellow Scot, Arthur Conan Doyle, published The Memoirs of Sherlock Holmes, in which readers were horrified to learn their hero had died falling into the Reichenbach Falls.


Alexander lived in the home of his elder brother, Tom, who was a doctor of medicine. Most of the Fleming family ended up living with Tom, leaving the eldest brother, Hugh, running the farm.

Alexander attended the Polytechnic School, where he studied business and commerce. He started in a class appropriate to his age, but his teachers soon realized he needed more challenging work. He was moved into a class with boys two years older than him and finished school at the age of 16.


Work and Medical School

Alexander’s business training helped him get a job in a shipping office, but he did not enjoy working there.

In 1901, at the age of 20, he inherited some money from his uncle, John Fleming. He decided to use the money to go to medical school; he wanted to become a doctor like his successful brother Tom.

First, he needed suitable qualifications to enable him to enroll at medical school. This did not present any great difficulties; he passed his exams with the highest marks of any student in the United Kingdom.


In 1903, age 22, Alexander enrolled at London’s St Mary’s Hospital Medical School, graduating with distinction three years later as Bachelor of Medicine, Bachelor of Surgery.

Rather than follow in Tom’s footsteps, Alexander was persuaded by Almroth Wright, an authority in immunology, to become a researcher in his bacteriology group at St Mary’s Hospital Medical School. While carrying out this research Fleming graduated, in 1908, with a degree in bacteriology and the Gold Medal for top student. St Mary’s Hospital Medical School then promoted him to the role of bacteriology lecturer.


Almroth Wright was interested in our bodies’ natural ability to fight infection. Fleming became particularly fascinated by the fact that although people suffer bacterial infections from time to time, our natural defences usually prevent infections from taking hold.


Discovery of Penicillin

In the month of August 1928, Fleming did something very important. He enjoyed a long vacation with his wife and young son.

On Monday, September 3, he returned to his laboratory and saw a pile of Petri dishes he had left on his bench. The dishes contained colonies of Staphylococcus bacteria. While he was away, one of his assistants had left a window open and the dishes had become contaminated by different microbes.


Annoyed, Fleming looked through the dishes and found something remarkable had taken place in one of them.

A fungus was growing and the bacterial colonies around it had been killed. Farther from the fungus, the bacteria looked normal. Excited by his observation, Fleming showed the dish to an assistant, who remarked on how similar this seemed to Fleming’s famous discovery of lysozyme.

Hoping he had discovered a better natural antibiotic than lysozyme, Fleming now devoted himself to growing more of the fungus. He identified that it belonged to the Penicillium genus and that it produced a bacteria-killing liquid. On March 7, 1929 he formally named the antibiotic penicillin.


Fleming published his results, showing that penicillin killed many different species of bacteria, including those responsible for scarlet fever, pneumonia, meningitis, and diphtheria. Furthermore, penicillin was non-toxic and it did not attack white blood cells.

Unfortunately, the scientific world was largely underwhelmed, ignoring his discovery.

Fleming faced a number of problems:

  • it was difficult to isolate penicillin from the fungus producing it

  • he could not find a way of producing penicillin in high concentrations

  • penicillin seemed to be slow acting

  • clinical tests of penicillin as a surface antiseptic showed it was not especially effective

  • Fleming’s boss, Almroth Wright, had a generalized dislike of chemists and refused to allow them in his laboratory. The presence of a skilled chemist would have been a huge benefit in terms of isolating, purifying, and concentrating penicillin.

Regardless of these issues, Fleming continued with some work on penicillin in the 1930s, but never made the breakthrough he needed to produce it in large, concentrated quantities. Others, however, did.

In the early 1940s a team of scientists led by pathologist Howard Florey and biochemist Ernst Boris Chain at the University of Oxford transformed penicillin into the medicine we know today.

In 1945 Alexander Fleming shared the Nobel Prize in Medicine or Physiology with Florey and Chain. The award was made:

“for the discovery of penicillin and its curative effect in various infectious diseases.”

In his Nobel Prize-winning speech in 1945, Fleming warned of a danger which today is becoming ever more pressing:


“It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them, and the same thing has occasionally happened in the body. The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug make them resistant.”


Fleming was always fulsome in his praise for Florey, Chain, and their team, and he downplayed his own role in penicillin’s story. Despite his modesty, he became a worldwide hero. Millions of people owed their lives to the antibiotic he had discovered.

In 1945 he toured America, where chemical companies offered him a personal gift of $100,000 as a mark of respect and gratitude for his work. Typically of Fleming, he did not accept the gift for himself: he donated it to the research laboratories at St Mary’s Hospital Medical School.


In 1944 Fleming was knighted and became Sir Alexander Fleming.

His wife Sarah died in 1949.

In 1953 Fleming married Dr. Amalia Koutsouri-Voureka, who was working in his research group at St Mary’s Hospital Medical School.

On March 11, 1955 Alexander Fleming died age 73 in London of a heart attack. His ashes were placed in St Paul’s Cathedral.


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