BACKGROUND
Frederick Griffith, established that there was a transforming principle in bacterial genetics in a ground-breaking experiment, performed in 1928.
He postulated that information could somehow be transferred between different strains of bacteria. This was long before the discovery of DNA and was an inspired piece of scientific detective work.
Griffith used two strains of Pneumococcus bacteria, type S and type R.
The S strain has a smooth polysaccharide coat which makes it resistant to the immune system of mice, whereas the R strain lacks this coat which will make it become destroyed by the immune system of the host.
Frederick Griffith, established that there was a transforming principle in bacterial genetics in a ground-breaking experiment, performed in 1928.
He postulated that information could somehow be transferred between different strains of bacteria. This was long before the discovery of DNA and was an inspired piece of scientific detective work.
Griffith used two strains of Pneumococcus bacteria, type S and type R.
The S strain has a smooth polysaccharide coat which makes it resistant to the immune system of mice, whereas the R strain lacks this coat which will make it become destroyed by the immune system of the host.
For the first stage of the transforming principle experiment, Griffith showed that mice injected with S died but when injected with R lived and showed few symptoms.
The next stage showed that if the mice were injected with type S that had been killed by heat, the mice all lived, indicating that the bacteria had been rendered ineffective.
The interesting results came with the third part of the experiment, where mice were injected with a mixture of heat killed S and lived R.
Interestingly enough, the mice all died, indicating that some sort on information had been passed from the dead type S to the live type R. Blood sampling showed that the blood of the dead mice contained both live type S and live type R bacteria.
Somehow the type S had been transformed into the type R strain, a process he named the transforming principle.
Griffith killed the pathogenic strain using intense heat and mixed the dead remains with the living bacteria of the non-pathogenic strain. As time went on, some of the living cells became pathogenic. This trait was then inherited by all descendants of the transformed bacteria.
Dead S bacteria and live R bacteria are both not harmful to the host by themselves, but were found to be harmful when mixed. Griffith was even able to extract both live S strains and live R strains from the blood of the dead mice killed by the combination. This helped Griffith conclude that there had to be some transforming factor that changed the R strain into the S strain.
The next stage showed that if the mice were injected with type S that had been killed by heat, the mice all lived, indicating that the bacteria had been rendered ineffective.
The interesting results came with the third part of the experiment, where mice were injected with a mixture of heat killed S and lived R.
Interestingly enough, the mice all died, indicating that some sort on information had been passed from the dead type S to the live type R. Blood sampling showed that the blood of the dead mice contained both live type S and live type R bacteria.
Somehow the type S had been transformed into the type R strain, a process he named the transforming principle.
Griffith killed the pathogenic strain using intense heat and mixed the dead remains with the living bacteria of the non-pathogenic strain. As time went on, some of the living cells became pathogenic. This trait was then inherited by all descendants of the transformed bacteria.
Dead S bacteria and live R bacteria are both not harmful to the host by themselves, but were found to be harmful when mixed. Griffith was even able to extract both live S strains and live R strains from the blood of the dead mice killed by the combination. This helped Griffith conclude that there had to be some transforming factor that changed the R strain into the S strain.