Alexander Fleming Discovers Penicillin

On Sept 3rd, 1928, Alexander Fleming noticed that a culture plate of Staphylococcus aureus had become contaminated with mold. What was interesting to the bacteriologist is that the mold seemed to inhibit the growth of bacteria on the culture plate. Alexander Fleming calle dthe substance "mould juice" and then later "penicillin" for the species of mold on the plate. He found that this juice was effective against the bacteria that causes pneumonia and gonorrhea. Unfortunately, when he published his findings in 1929, very few scientists were impressed with the discovery. Fleming admitted that it was difficult to isolate the mould juice and therefore it would be difficult to mass produce in large quantities.

alex fleming

Before Fleming performed his experiments, scientists were not even certain of the origin of disease. In the 19th century, doctors believed that illness was spread through the air, an idea called the Miasma Theory, and then later proposed that illness was caused by an imbalance in the blood. This idea, the Humoral Theory of illness, lead to treatments such as bloodletting, where patients would be drained of blood in order to "balance their humors."

In the late 19th century, several scientists contributed to the current understanding of the Germ Theory. Ignaz Semmelweis confirmed that hand washing could prevent the spread of infection. Louis Pasteur established that microorganisms caused disease, when he showed that bacteria would grow in S shaped flasks if given nutrients. As scientists became aware of these microorganisms that lived around us that could make us sick, they turned their research toward finding a way to cure a person of the pathogens.

It wasn't until 12 years later that the substance was revisited. A team of scientists at the University of Oxford were able to isolate the element chemically. Howard Florey and Ernst Chain injected mice with a lethal dose of a streptococcus bacteria and then treated one group of mice with injections of penicillin. The untreated mice died within 18 hours, but the treated mice survived.

Now that scientists could isolate the substance and had evidence that it could cure bacterial infections, they needed to find a company who would mass produce the substance. The U.S. government became interested during World War II because of the need to treat wounds and reduce casualties. This interest lead to the eventual development of mass produced penicillin by a pharmaceutical company named Pfizer. By the end of 1945, Pfizer was producing more than half the world's supply of penicillin.

Penicillin was widely distributed to fight infections and treat diseases such as syphilis and gonorrhea. With access to this new drug as well as better antiseptic techniques, infections were no longer fatal. Howard Florey, Ernst Chain, and Alexander Fleming shared the 1945 Nobel Prize for the discovery and isolation of penicillin which was then used to treat infection.


1.   Who is credited with the discovery of penicillin?
a.  Merlin Pryce                         b. Ignaz Semmelweis 
c.  Louis Pasteur                        d.   Alexander Fleming

2.  The discovery of penicillin was:
a.  a careful experiment using the scientific method
b.  a chance discovery
c.  delayed due to the inability to culture a specific mold

3. Which treatment would a doctor who believed in the "Humoral Theory" most likely prescribe?
a. opening windows to let in fresh air            b. bleeding with leeches                

4.  Why did Fleming not continue his research on penicillin?
a.  he could not isolate the antibacterial element
b.  the mold was unstable and dangerous
c.  his work was taken over by other scientists

5.   In Florey and Chain's experiment, mice that received an injection of penicillin:
a. died      b. survived   

6.  What event prompted scientists to revisit penicillin to try to mass produce it?
a.  a diphtheria outbreak      b.  Alexander Fleming’s death c.  World War II          d. The Civil War       

7. What prize was awarded to Fleming, Florey, and Chain?
a. 100,000 dollars        b. The Nobel Peace Prize       c. The Scientific Achievement Award

8. Arrange the events in the correct order:

___ Discovery of a substance in mold that killed bacteria.
___ The development of the germ theory.
___ Mass production of penicillin by Pfizer
___ Isolation of the substance in mold that killed bacteria

9. The 20th century (1945-2000) was a time when antibiotics were thought to be the cure-all for infections. Unfortunately, in the 21st century, scientists have observed that many bacteria that were treatable with antibiotics like penicillin were becoming resistant to the drugs. What is the most likely result of bacteria developing these resistance?
a. more people will die of infections      b. more bacteria will accumulate in the environment     c. humans will develop resistance to bacteria

10. Do you agree with awarding the prize with all three scientists, or should the award have only gone to Fleming? Why or why not? (Defend your position with 1-2 sentences.)