What is Griffith experiment?

                    Griffith's experiment

In 1928 by Frederick Griffith, experimented that bacteria are capable of transferring genetic information through a principle  known as transformation. Griffith used two strains of pneumococcus (Streptococcus pneumoniae) bacteria which infect mice – 
a. type III-S (smooth) which was virulent
b. type II-R (rough) strain which was nonvirulent.

Experiment-
The III-S strain covered by polysaccharide capsule , while the II-R strain did not have that protective capsule and was defeated by the host's immune system. In this experiment, bacteria  from the III-S strain were heat killed and their remains were added to II-R strain bacteria. The combination was able to kill its host. Griffith was also able to isolate both live II-R and live III-S strains of pneumococcus from the blood of these dead mice. 

Conclusion- Transfering  principle" was transferred from the heat-killed S to the R strain and observed that the transforming principle observed was the DNA of the III-s strain bacteria. While the bacteria had been killed, the DNA had survived the heating process and was taken up by the II-R strain bacteria. The III-S strain DNA contains the genes that form the protective polysaccharide capsule. Equipped with this gene, the former II-R strain bacteria were now protected from the host's immune system and could kill the host.

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