Transforming Principle
▪ Frederick Griffith (1928) conducted experiments with Streptococcus pneumoniae (bacterium causing pneumonia).
▪ He observed two strains of this bacterium—one forming smooth shiny colonies (S-type) with capsule, while other forming rough colonies (R-type) without capsule.
▪ When live S-type cells were injected into mice, they died due to pneumonia.
▪ When live R-type cells were injected into mice, they survived.
▪ When heat-killed S-type cells were injected into mice, they survived and there were no symptoms of pnuemonia.
▪ When heat-killed S-type cells were mixed with live R-type cells and injected into mice, they died due to unexpected symptoms of pneumonia and live S-type cells were obtained from mice.
▪ He concluded that heat-killed S-type bacteria caused a transformation of the R-type bacteria into S-type bacteria but he was not able to understand the cause of this bacterial transformation.
▪ Griffith’s experiment on transformation
