Final answer:
Frederick Griffith concluded from his transformation experiments that a 'transforming principle' present in dead pathogenic bacteria could convert live nonpathogenic bacteria into a pathogenic form. This principle was later identified as DNA.
Step-by-step explanation:
Griffith's Transformation Experiments Conclusion
Frederick Griffith concluded from his transformation experiments that a substance could be transferred from dead pathogenic Streptococcus pneumoniae bacteria to live nonpathogenic bacteria, thereby transforming them into a pathogenic form. This transformation suggested that there was a "transforming principle" capable of altering the characteristics of the bacteria receiving it. Griffith's groundbreaking work laid the foundation for future discoveries that identified DNA as this transforming principle, which was later confirmed by the experiments of Avery, MacLeod, and McCarty.
In his experiments, Griffith worked with two strains of Streptococcus pneumoniae: the nonpathogenic R strain, lacking a polysaccharide coat, and the pathogenic S strain, having a capsule that gives it a smooth appearance. He observed that when live R strain was injected into mice, they survived; similarly, mice injected with heat-killed S strain survived. However, when he injected a combination of live R strain and heat-killed S strain, the mice died, and surprisingly, only live pathogenic S strain bacteria were recovered from the dead mice. This indicated that the R strain was transformed into the S strain by some factor that had been present in the heat-killed S strain. Griffith named this factor the "transforming principle".