Question

Explain Griffith's transformation experiments. What did he conclude from them?

Short answer

Griffith determined that after coming into touch with the heat-killed SIII strain, the non-virulent RII strain was changed into virulent SIII. Transformation was used to characterize this phenomena.

Step-by-step solution

Step:1 Introduction

F. Griffith was the first to undertake transformation tests (1928). On the basis of their appearance in colonies, he chose two bacterium strains (Streptococcus pneumonia), S (smooth) and R (rough); however, S was virulent while the other strain was non-virulent (causing no infection).

Step:2  Explanation of the solution

The polysaccharide capsule, which is present in virulent strain S but absent in non-virulent strain R, is required for Pneumococcus virulence. It was discovered that when the SIII strain was injected into mice, they died of pneumonia, whereas the injected RII strain caused no sickness and the animals survived. Injecting a heat-killed virulent SIII strain revealed that infectivity was lost following heat killing. Mice injected with a mixture of RII (alive) and SIII (heat-killed) bacteria perished, and the pathogenic SIII variety was isolated. Mice died after being injected with the isolated SIII strain.