1. Alexander Fleming discovered penicillin in England in 1928. It was a substance produced by the mold, Penicillium. He was a doctor at St. Mary’s Hospital in London.
  2. The mold contaminated one of Fleming’s petri dishes growing Staph bacteria. Fleming noticed areas around the mold were clear. He thought a substance produced by the mold killed the bacteria. He named the substance penicillin.
  3. Penicillin was unstable. Fleming could not extract it. He stopped working on penicillin by 1932.
  4. In 1939, scientists at the University of Oxford read about Fleming’s 1928 discovery. They were curious.
  5. They were able to extract penicillin and work with it.
  6. At the time, World War II had started. Nazi Germany was bombing England in 1940.
  7. In 1941, Oxford scientists came to the United States to continue their research. They also wanted to find a pharmaceutical company to produce large quantities of penicillin.
  8. British scientists worked with scientists at the U.S. Department of Agriculture (USDA) lab in Peoria, Illinois. After searching around the world for new Penicillium strains, they found one in Peoria from a moldy cantaloupe purchased at a local market.
  9. The Peoria strain became the strain that produced most of the penicillin during World War II. By D-Day on June 6, 1944, 100 Billion Units were being made each month. That was enough penicillin to treat 40,000 infections.
  10. Anchor book: The Mold in Dr. Florey’s Coat by Eric Lax (2005)

STORY by Judith Stanford Miller, editor

Nov. 10, 2020 – Thousands of soldiers’ lives were saved in the days and weeks following the D-Day invasion on June 6, 1944. Dr. Harold Florey and scientists at the University of Oxford in England were curious about a substance Alexander Fleming discovered ten years earlier. Fleming was a physician and microbiologist at St. Mary’s Hospital in London. That substance was penicillin, a byproduct of the Penicillium mold, the mold in Dr. Florey’s coat.

It’s not possible to verify the well known story that in 1928, Fleming accidentally discovered penicillin by leaving the lid off a petri dish, growing Staph bacteria, when he went on vacation. The dish was next to an open window in his lab. Eric Lax, author of The Mold in Dr. Florey’s Coat, said the story of how Fleming discovered penicillin is lost to history. But Fleming did discover penicillin.

The Mold in Dr. Florey’s Coat by Eric Lax (263 pages) is an excellent account of the discovery and mass production of penicillin during WWII. (Photo of book: Redwood Learn)

The petri dish had been contaminated with a mold. Around the mold growth, Fleming noticed the area was clear. Staph bacteria were not growing there. He surmised (thought or deduced) that something from the mold killed the bacteria. He tried extracting the substance. He called it penicillin because the mold was from the genus, Penicillium. But the substance was unstable. He could not work with it. He wrote a paper about it in 1929. By 1932, his had stopped working with penicillin.


Years later, scientists in the Dunn School of Pathology lab at the University of Oxford in England read Fleming’s 1929 paper. They were curious about penicillin. Dr. Harold Florey and Ernst Chain took up where Fleming left off. They began extracting penicillin from Penicillium mold.

By 1940, Europe was at war. England was defending itself against Nazi Germany’s quest to create a new world order with a reunited German Empire in control. Florey and Chain worried their lab would be bombed as Germany conducted a “Blitz” in fall 1940 by dropping bombs on London and other British cities for 57 consecutive nights. They decided to rub Penicillium mold on their lab coats in case everything was destroyed in their lab.

England successfully defended itself. Germany never took control of England. But World War II continued.


After isolating only small amounts of penicillin, Dr. Florey and another scientist came to the United States in summer 1941 seeking pharmaceutical companies that would agree to produce penicillin. They also sought help from the U.S. government to continue their research on how to produce large quantities of penicillin from the mold.

The U.S. Department of Agriculture (USDA) lab in Peoria, Illinois was the perfect place to continue their penicillin research. Six months later after Japan attacked the U.S. Navy in Pearl Harbor, Hawaii on Dec. 7, 1941, America was also at war. Large quantities of penicillin would be needed.

The Peoria lab searched around the world for Penicillium strains that would be super strains producing large amounts of penicillin. In summer 1943, they struck gold at home. A moldy cantaloupe from a Peoria market near their lab had a strain of Penicillium (Penicillium chrysogenum) that produced 200 times the amount of previous strains. And then after applying ultraviolet (UV) light, the strain produced 1,000 times the amount of penicillin. This strain supplied most of the world’s supply of penicillin during World War II and in the years after the war.

This photo of a moldy orange was taken in summer 2020. It could be a strain of Penicillium but would have to be identified in a lab. Think of a cantaloupe covered with green mold as shown in the picture above and that is what the NRRL lab found in 1943 that eventually supplied the world with penicillin. (Photo: Redwood Learn)

In Brooklyn, New York, Pfizer, a pharmaceutical company, converted an old ice factory to a factory producing penicillin. They perfected deep tank fermentation. Other companies – Abbott Laboratories, Merck and Squibb – also produced penicillin. Eventually, more than 20 pharmaceutical companies were supplying the Allies with penicillin.

This is page 7 in the June 5, 1944 issue of LIFE Magazine. It’s an advertisement for penicillin made by “The House of Squibb.” Note the issue came out one day before D-Day. The women in the photo are packaging penicillin. The ad says there is now enough penicillin for limited amounts for civilians. (Photo of page by Redwood Learn)

By D-Day on June 6, 1944, 100 billion units of penicillin were being produced in total each month. That amount was enough to treat 40,000 infections. It saved thousands of soldiers’ lives.

Soon it was available to the public. Mass production resulted in a price decrease from $200 to treat one case to $6. By the late 1940s, Pfizer was producing more than one-half of the world’s supply of penicillin.

Animal Cells, Plant Cells and Bacteria

The cell is the basic unit of life. Cells in animals and humans differ from cells in plants.

Animal and Human cells

Animals and humans have billions of cells in their bodies. There are more than 200 different types of cells in the human body. Cells come in many different shapes depending on their function. For example, red blood cells (RBCs) carry oxygen to every cell in the body so cells can perform their intended function. Nerve cells look much different from red bloods cells. But every cell needs oxygen to live and divide.

All cells have common parts. Every cell has a cell membrane that surrounds the cell. At the center of the cell is the nucleus where DNA directs the cell. Between the nucleus and the cell membrane is cytoplasm where proteins are made and metabolism takes place.

Plant Cells

Plant cells differ from animal cells. To give plants their rigid structure, plant cells are surrounded by a cell wall that is a layer over the cell membrane. And plant cells have chloroplasts, structures that are needed so plant cells can absorb sunlight and carbon dioxide from the air to make their own food, a process called photosynthesis. The end product of photosynthesis is oxygen that plants release into the air for animals and humans to breathe.

Bacteria are microorganisms

Bacteria are microorganisms, living cells that are too small to be seen by the naked eye.

circles (clusters) – Staph
circles (chains) -Strep

Bacteria come in three general shapes – rods, circles and spirals. Bacteria are single cells that have a simpler structure than animal and plant cells. Billions of bacteria live normally in animals and humans. But some can be harmful. An example of bacteria that can be both harmful and beneficial is Escherichia coliE. coli.

Billions of E. coli bacteria are needed in the intestines to maintain health. However, a few types of E. coli are harmful to the body if ingested through contaminated food. These harmful E. coli produce toxins that can result in serious disease.

E. coli are shaped as rods.

Other examples of bacteria that can be both beneficial and harmful are staph and strep. Billions of staph bacteria are normal on the skin. But some types of staph cause nasty infections of the skin. When a wound is infected, it swells, becomes red and hurts. Pus forms as a way for the body to get rid of bacteria but antibiotics are often needed to cure the infection.

There are many types of normal strep. But a harmful type of strep causes strep throat, a painful infection that needs to be treated with antibiotics, such as penicillin. Strep bacteria can also cause pneumonia, a serious lung infection.

Staph and strep are shaped as circles. Staph bacteria look like clusters of grapes. Strep bacteria look like chains.


  1. microbiologist: (noun) – a person who is an expert in Microbiology, the study of microorganisms (bacteria, fungi, parasites and viruses)
  2. pharmaceutical: (adj.) – related to pharmacy (noun form): drugs or medicine, in this context, a company that makes drugs, such as penicillin
  3. verify: (verb) – to confirm, to prove true
  4. accidentally: (adverb) – by accident, not on purpose
  5. contaminated: (verb) – spoiled with something that was not supposed to be there
  6. unstable: (adj.) – not stable, breaks down easily
  7. consecutive: (adj.) – one after the other
  8. beneficial: (adj.) – good, helpful


  1. What is the genus of the mold that produces penicillin, an antibiotic?
  2. Who was the first scientist to discover penicillin as a byproduct of a mold?
  3. Where was penicillin discovered?
  4. When was the mass production of penicillin achieved?
  5. Why was penicillin urgently needed in the 1940s?
  6. When it was first produced, what bacteria did penicillin kill?
  7. What is penicillin still used for today?
  8. What was Dr. Howard Florey’s contribution to the production of penicillin?


  1. How can you tell the difference between staph and strep bacteria?
  2. Why did Dr. Florey and his team of scientists rub Penicillium spores on their coats?
  3. Why was the mass production of penicillin so important during World War II?