Fred griffith studied two strains of streptococcus pneumonia,one that causes a lethal infection when injected into mice, and a second that is harmless. He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection. But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse. what did griffith conclude from this experiment?

Griffith performed the experiment on infection caused by the Streptococcus pneumonia in mice. He selected two strains of bacteria: avirulent strain called R strain and a virulent strain called S strain.

During the experiment, when he heat-killed the S bacteria, added it to the R strain bacterial plates and then injected the bacteria into mice, he found that the bacteria killed the mice. He was astonished to see the result as the harmless bacteria killed the mice.

He concluded that adding the S bacteria produced some molecule which could have transformed the harmless bacteria to harmful bacteria. He called the transforming molecule as transforming principle.

Griffith performed the experiment on two strains of Streptococcus pneumonia in which one strain is avirulent called R strain and another virulent strain called S strain.

When Griffith killed the S bacteria (virulent) by heat and added it in the R strain Petri dishes and then injected the bacteria to mice, the mice killed. This amazed him as to how the avirulent bacteria killed the mice ?

He concluded that there was some principle which transformed the avirulent bacteria to virulent bacteria and thus called the principle as transforming principle.