Example of Scientific method: Flemming’s discovery of Penicillin

In the last post we discussed the steps involved in a scientific method. In this post we will discuss the same thing with an example. As I mentioned, keen observation of surroundings is the key quality of a scientist. Here I am citing an example that tells us the value of an unexpected observation.

Penicillin discovery
Penicillin discovery 
 Infant jaundice is a condition very common in infants that is characterized by yellowish skin colouration. The reason for infant jaundice is the presence of high levels of bilirubin in the blood. This can lead to brain damage and death. Bilirubin is a degradation product of hemoglobin and that is degraded and excreted by liver. In infants, immature liver cannot convert this bilirubin and thus bilirubin accumulates leading to infant jaundice. Now our point, how infant jaundice is treated? A nurse in England (Rochford Hospital in Essex) found out that exposure of infants intermittently to mild sun rays can significantly reduce their yellowish skin colour. Later scientists experimented on this simple observation and found out that UV rays in the sunlight could degrade bilirubin into non-toxic products and can be readily excreted in infants. Till now, for infant jaundice the same treatment is given all over the world. All started from a simple observation ultimately became a treatment modality followed all over the world for a fatal disease.

Scientific method at work

Here we will discuss the steps involved in the discovery of antibiotic penicillin by Alexander Flemming (1928) During Second World War, penicillin was widely used and could save millions from wound infections.
Discovery of penicillin was serendipity or an accidental discovery. Flemming was working on different aspects of growth of bacterium namely Staphylococcus that cause throat infection. He plated bacterial colonies on a medium in petri-plates for an experiment. Next day, he found out that his bacterial cultures were ruined by a blue green fungus, Penicillium notatum colonies. Instead of throwing away the plates, he made an important observation that bacterial colonies could not grow around this fungal colonies. He wants to know the reason. He asked why?
Now let us check out
How Flemming solved his problem using scientific method?

Step I: observation and defining the problem. 
Flemming’s observation was bacterial colonies could not grow around fungal colonies.

Step II: Formulate a hypothesis: 
Fungal colonies can synthesise certain chemicals that can inhibit bacterial growth (possible answer).

Step III: Testing hypothesis by conducting experiments.
Experimental Design: Two culture tubes A and B with nutrient broth for bacterial growth.
To the first tube, let it be A (“test” tube), he added fungus and allowed to grow for few days.
He kept second tube, tube B as control (remained sterile)
After few days, he filtered the broth to remove any fungal cells and allowed bacteria to grow in both tubes A and B.

Step IV: Collect and record data.

In the A tube (test), no bacterial growth were observed.
In the B tube (control), bacterial growth was observed.

Step V: Analyse and interpret data and draw conclusions.

He concluded that in tube A, previously grown fungal cells secreted certain chemicals that inhibited the growth of bacteria. In tube B, bacteria could grow as no fungal colonies were grown before. Thus hypothesis put forward was correct.

Step VI: Report results or theorising:
Later he could isolate antibiotic penicillin from Penicillium notatum colonies. This discovery was during Second World War. Penicillin was called “wonder drug” as millions of lives were saved from bacterial wound infection due to the discovery of this antibiotic. Let us summarise these accidental unexpected discoveries as said by famous microbiologist Louis Pasteur “Luck favours the prepared mind”.
Previous Post Next Post