Question

Describe the experience of the little boy in
the grove​

Answer 1

Fredrick Griffith in 1928 conducted a series of experiments with the bacterium, Streptococcus pneumoniae. This bacterium has two strains − S strain and R strain. The S strain produces a mucus polysaccharide coat while the R strain does not. This polysaccharide coat is responsible for virulence.

When the S strain was injected into mice, they died of pneumonia but mice injected with the R strain did not.

When Griffith injected a mixture of heat-killed S strain and live R stain, the mouse died.

From the above experiment, Griffith concluded that R strain bacteria was somehow transformed by the heat-killed S strain. The S strain transferred some 'transforming principle' to the live R strain which enabled the R stain to produce the polysaccharide coat (virulence factor).

Although Griffith could not deduce the biochemical nature of the transforming principle, he concluded that the transformation of the avirulent strain into a virulent one was because of the transfer of genetic material.