Frederich Griffith claimed that R-strain Streptococcus pneumoniae had been transformed by heat killed
S-strain bacteria. Explain the findings.
Transformation was first studied by Frederick Griffith in 1928. He conducted experiments
with streptococcus pneumoniae, the bacterium responsible for pneumonia.
1. He observed two strains of this bacterium, some produce shiny colonies (S)
while others produce rough colonies (R). Strain bacteria have a mucous (polysaccharide)
coat, while R-strain does not have.
2. The S-strain bacteria are virulent while the R-strain bacteria are non-virulent.
3. When live S-type bacteria were injected into mice, they died from pneumonia.
4. Mice injected with the R-strains, mice survived.
5. Heat killed S-strain bacteria were injected into mice, did not kill them.
6. S-strain (heat killed) were mixed with R-strain (live) and then injected into
mice, the mice died of puneumonia.
7. He isolated living S bacterium from the dead mice. He concluded that the R-strain
bacteria had somehow been transformed by the heat killed S-strain bacteria. Some
transforming principle transferred from the heat killed S-strain bacteria. It changed
the R-bacteria into S-bacteria, so R-bacteria were able to produce a smooth polysaccharide
coat and became virulent.