In the light of Griffith’s experiment, explain the action of two stains of Diplococcus pneumoniae and give his conclusion.
Solution
Griffith Experiment : The first series of experiments were performed by a British physian 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 Stype of bacteria were injected into healthy mice, the mice developed pneumonia and died. Thus S-type is virulent or pathogenic. When R-type of 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 of 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 transformation.
He named that something as transforming principle. It was later proved that this transforming principle is DNA.
