Submit Article |Resources | Link to us | Sitemap | Search | Language
Back to Home
Home >> Genetic Material >>Griffith's Experiment on Genetic Material
Back to Home

Griffith's Experiment on Genetic Material - In 1928, Frederick Griffith reported that heat killed bacteria of one type could "transform" living bacteria of a different type. Griffith demonstrated this transformation using two strains of the bacterium Streptococcus pneumoniae. One strain produced smooth colonies on media in a Petri plate. These strains produce a slimy coating consisting of polysaccharide.

This polysaccharide is responsible for protection of the strain during adverse conditions. It causes a fatal pneumonia. Another strain (R) produces rough colonies on media in a Petri plate. This strain does not produce any slimy layer of polysaccharide. This strain does not cause any disease. Griffith conducted four experiments involving smooth strain (S) and rough strain (R) of S. pneumonjae and mice. In set one experiment, he injected mice with live smooth strains (S) of S. pneumonjae and observed that mice died of pneumonia. In another set he injected live rough strain (R) of S. pneumonjae and observed that mice did not contract pneumonia. In the third set, he injected smooth strain (S) of S. pneumonjae which are killed by heating at 60°C for 3 hours and observed that mice did nm contract pneumonia.

This experiment indicates that the bacteria was dead and did not have any virulence further. Finally, a sample of heat killed smooth strain (S), incapable of causing the disease, was mixed with live avirulent rough strain (R) of S. pneumoniae and the mixture was injected into a mice. This time a wholly unexpected result was obtained. The mice contracted pneumonia instead of being healthy. In addition, from this group, a large number of live smooth strain (S) of S. pneumoniae were isolated.

  

The experiment result suggests that a component of the heat killed smooth strain got (some transformation of pneumonia­ causing agent transferred into rough strain. Importantly, the live virulent bacteria obtained at the end of this experiment were S­type. The explanation cannot be that the type R in original inoculums regained their ability to synthesize their capsular polysaccharide. If this had happened then the resulting bacteria would have been type R, instead of smooth.

 
 

 
Submit Article |Resources | Link to us | Sitemap | Search | Language
English|Français|Español|Deutsch|Italiano|Portugues|Japanese|Korean|Sim-Chinese| Language