In Streptococcus pneumonia
(a) virulent form is smooth.
(b) virulent form is rough.
(c) nonvirulent form is capsulated.
(d) all forms are rough.

Dear student

Option a is correct. 

Griffith (1928) described the phenomenon of bacterial transformation. He experimented with smooth and rough strains of Streptococcus pneumoniae

The smooth strains of Streptococcus pneumoniae were virulent and pathogenic. It causes disease called Pneumonia. 

Details of Griffith's experiment is given below :

Transforming Principle

  • Griffith performed experiments with the bacteria Streptococcus pneumoniae. This bacterium has two strains − S strain and R strain.

S strain Bacteria

R strain Bacteria

  • Produce smooth colonies on culture plate

  • Produce rough colonies on culture plate

  • Have a polysaccharide coat

  • Do not have a polysaccharide coat

  • Virulent (causes pneumonia)

  • Non-virulent (does not cause pneumonia)

  • Griffith’s experiment

  • Live R strain in the presence of heat-killed S strain produce virulence because somehow R strain bacteria is transformed by heat-killed S strain bacteria. Hence, it was concluded that there must be transfer of genetic material.

Biochemical Nature of Transforming Material

  • Avery, McLeod, and McCarthy worked to determine the biochemical nature of genetic material responsible for transformation.

  • This suggests that DNA has to be the genetic material.

R strain of Streptococcus pneumonia is not virulent as it does not produce polysaccharide coat (virulence factor).

S strain of Streptococcus pneumonia is virulent due to the presence of polysaccharide capsule.


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