Question

In the light of Griffith’s experiment, explain the action of two stains of Diplococcus pneumoniae and give his conclusion.

Answer 1

Griffith Experiment: The first series of experiments was performed by a British physician, F. Griffith, in 1928, using the bacterium Diplococcus pneumoniae, which causes pneumonia in mammals.

There are two types of strains;

1. S-type is capsulated and smooth and
2. R-type is non - capsulated and rough.

When S-type of bacteria were injected into healthy mice, the mice developed pneumonia and died. Thus type of bacteria were injected into healthy mice, and the mice developed pneumonia and died. Thus S-type is virulent or pathogenic. When R-type bacteria were injected into healthy mice, they did not cause pneumonia. Thus R-type is avirulent or non-pathogenic.

Conclusion: Griffith concluded that living R-type bacteria must have picked up something from the surrounding medium that contains heat-killed S-type, and got changed to S-type. This change is due to the phenomenon of transformation. He named that something as a transforming principle. It was later proved that this transforming principle is DNA.