• Sheela Srivastava


In 1928, Fred Griffith, a British pathologist was studying the pathogenicity of pneumococcal infections in mice that also causes pneumonia in humans. Based on the disease response, pneumococcal strains could be classified as virulent or disease-causing and avirulent or non-pathogenic. He observed that the virulent strains of the causative organism, Pneumococcus (Streptococcus) pneumoniae can be easily distinguished from the avirulent ones by the fact that they produced smooth glistening colonies on agar surfaces and thus were referred to as S strains. Several such S strains could be identified based on a polysaccharide capsule that carries antigenic properties. Such strains were labeled as SI, SII, SIII, etc., basically differing in the composition of their capsular polysaccharides, and thus, eliciting different antigenic responses.


Transformation Frequency Competence Development Deoxyribose Nucleic Acid Type Bacterium Autolytic Enzyme 
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Further Readings

  1. Avery OT, Macleod CM, McCarty M (1944) Studies on the chemical nature of the substance inducing transformation of pneumococcal types. I. Induction of transformation by a deoxyribonucleic acid fraction isolated from pneumococcus type III. J Exp Med 79:137–158PubMedCrossRefGoogle Scholar
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  12. Steinmoen H, Knusten E, Havarstein LS (2002) Induction of natural competence in Streptococcus pneumoniae triggers lysis and DNA release from a subfraction of cell population. Proc Natl Acad Sci U S A 99:7681–7686PubMedCrossRefGoogle Scholar
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Copyright information

© Springer India 2013

Authors and Affiliations

  1. 1.Department of GeneticsUniversity of Delhi, South CampusNew DelhiIndia

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