Click image to open full size
Medical Science
Alexander Fleming: Discoverer of Penicillin
The mold, the petri dish, and the antibiotic revolution
Related Worksheets
Related Cheat Sheets
Alexander Fleming was a Scottish physician, microbiologist, and pharmacologist whose careful observation changed medicine. In 1928, he noticed that a mold contaminating a Petri dish had killed nearby bacteria instead of ignoring it as a failed experiment. That mold, Penicillium, led to the first widely used antibiotic, penicillin. His discovery mattered because it gave doctors a powerful way to treat many deadly bacterial infections.
Key Facts
- Alexander Fleming lived from 1881 to 1955 and worked as a physician and microbiologist in Britain.
- In 1928, Fleming observed that Penicillium mold prevented the growth of Staphylococcus bacteria on a Petri dish.
- Penicillin is an antibiotic, meaning it kills bacteria or stops them from growing.
- Fleming did not mass-produce penicillin himself, but Howard Florey and Ernst Chain helped purify and develop it for medical use.
- Fleming, Florey, and Chain shared the 1945 Nobel Prize in Physiology or Medicine for penicillin.
- Antimicrobial resistance can develop when bacteria survive drug exposure and pass on resistance traits to later generations.
Vocabulary
- Antibiotic
- A medicine that kills bacteria or slows their growth.
- Penicillin
- An antibiotic originally derived from Penicillium mold that is effective against many bacterial infections.
- Penicillium
- A group of molds that includes species able to produce the antibiotic penicillin.
- Bacterial inhibition
- The slowing or stopping of bacterial growth, often seen as a clear zone around an antibiotic source on a culture plate.
- Antimicrobial resistance
- The ability of microbes such as bacteria to survive medicines that once killed them or stopped their growth.
Common Mistakes to Avoid
- Thinking Fleming invented all antibiotics is wrong because he discovered penicillin, while many other antibiotics were found or developed later by other scientists.
- Saying penicillin kills viruses is wrong because antibiotics act on bacteria, not viruses such as influenza or the common cold.
- Ignoring Florey and Chain is wrong because they played a major role in purifying, testing, and scaling up penicillin for medical treatment.
- Using antibiotics for every illness is wrong because unnecessary use increases selection for resistant bacteria and can make future infections harder to treat.
Practice Questions
- 1 Fleming discovered penicillin in 1928 and shared the Nobel Prize in 1945. How many years passed between the discovery and the Nobel Prize?
- 2 Alexander Fleming lived from 1881 to 1955. How old was he when he died, and how old was he in 1928 when he made the penicillin observation?
- 3 A Petri dish has a circular clear zone around a Penicillium colony where bacteria did not grow. Explain what this clear zone suggests about the mold and why Fleming's interpretation was scientifically important.