Practice question

Griffith chose Streptococcus pneumoniae, then called pneumococcus, diplococcus causing lobar pneumonia, because it exhibited two colony morphologies linked to virulence. Smooth colonies produce thick polysaccharide capsule preventing phagocytosis, virulent. Rough colonies lack capsule due to mutation in capsule biosynthesis enzymes, avirulent. Capsule antigens defined serotypes II and III used in cross-transformation tests. This organism was amenable to mouse infection model and grew on simple media. Its natural competence later made it ideal for transformation studies by Avery and for discovery of DNA as genetic material.