Experiment Method of How Dr Alexander Fleming Discovered Penicillin

You must have heard about penicillin the wonder drug that cures many bacterial diseases. This drug was accidentally discovered by Sir Alexander Fleming while he was studying the growth of a certain type of bacterium. 



Step 1: Fleming was studying the growth and reproduction of the bacterium Staphylococcus is dishes containing agar to which nutrients had been added.

Step 2: He observed that a mould Penicillium was also growing in some of the dishes. (The mould had got the dishes by accident) In addition, he observed a clear zone around the area where the mould grew, indicating that the bacteria growing there had died.

Step 3: What had caused the bacteria to die?

Step 4: Fleming put forward a hypothesis: the mould produced a chemical which diffused into the surrounding agar and killed the bacteria.

Step 5: To test his hypothesis he designed an experiment. He grew the mould in a liquid nutrient broth so that the chemical it produced would diffuse into the broth. He added some of this broth minus the mould to the bacteria.

Step 6: He observed that the bacteria died after broth was added.

Step 7: Was there something in the nutrient broth that caused the bacteria to die?

Step 8: To find out the answer to this question; he added some nutrient broth in which no mould had been grown to the bacteria.

Step 9: The bacteria did not die.

Step 10:  The confirmed that Fleming’s hypothesis was correct. It was tested by other scientists. The chemical was isolated and named penicillin.