Question

Describe Frederick Griffith's experiment on Streptococcus pneumoniae.

Answer 1

1. In 1928, a British medical officer Frederick Griffith performed an experiment on bacterium Streptococcus pneumoniae that causes pneumonia in humans and other mammals.
2. He observed that the bacteria have two colonie:
   1. R strain: Rough colonies, non-virulent. nonpathogenic and non capsulated
   2. S strain: Smooth colonies, virulent, pathogenic and capsulated.
   3. He performed following experiments:
3. Mice injected with R-cell bacteria - mice survived:
   1. Mice were injected with S-cell germs and died.
   2. S-cell bacteria were killed by heat injection in mice, yet the mice survived.
   3. Mice injected with heat killed S-cell bacteria while retaining live R-cell bacteria - mice died, and Giffith recovered live S-cell bacteria from their blood.
4. Griffith came to the conclusion that R-strain bactrium must have turned into living S strain via the transforming principle.