The Graphite Experiment

Frederick Griffith's Graphite Experiment on Tryptococcus Pneumonia

• Frederick Griffith, a British medical officer, conducted an experiment in 1928 on the bacterium Tryptococcus Pneumonia.
• Tryptococcus Pneumonia is a bacterium that causes pneumonia in humans and other mammals.
• There are two strains of Tryptococcus Pneumonia: S strain and R strain.
• The S strain has a polysaccharide coat, making it virulent, pathogenic, and encapsulated.
• The R strain is non-virulent, non-pathogenic, and non-capsulated.
• Griffith performed four experiments using these bacteria.
• In the first experiment, he injected the R strain into mice, and the mice did not suffer from pneumonia and survived. This was because the R strain does not have a polysaccharide coat that can be destroyed by the mice's immune system.
• In the second experiment, Griffith injected the S strain into mice, and the mice developed pneumonia and died. This was because the S strain's polysaccharide capsule protected it from destruction by the mice's immune system.
• In the third experiment, Griffith heated the S strain, which killed it.
• In the fourth experiment, Griffith injected a mixture of the heat-killed S strain and the live R strain into mice.
• Surprisingly, the mice developed pneumonia and died, and when Griffith examined their bodies, he found live S strain bacteria.
• This led to the discovery of transformation, where the genetic material from the heat-killed S strain was taken up by the live R strain, transforming it into the S strain.
• This experiment provided important evidence for the concept of genetic transformation in bacteria.