Streptococcus

Common properties

• Gram-positve
• Ovoid to spherical in shape, occurring as pairs or chains
• Nonmotile
• Catalase-negative
• Most are facultative anaerobes, but grow fermentatively even in presence of oxygen.
• Fastidious, cultured on blood agar

Classifications

By haemolytic properties

alpha - degradation of hemoglobin -> green pigmentation around colonies

beta - gross lysis of RBC -> clear ring around colonies

gamma - no color changes (nonhemolytic)

By serology (Lancefield)

Cell wall polysaccharide - C-carbohydrate (linked covalently to peptidoglycan

Lancefield classifies (mostly beta-haemolytic strep) into group A to U.

Important groups -

Group A - strep pyogenes (beta-hemolytic)

Group B - strep agalactiae (beta-hemolytic)

Group D - strep bovis (alpha or gamma-hemolytic)

Other - strep pneumoniae (alpha-hemolytic)

Other - strep mutans (alpha or gamma-hemolytic)

Things to revise/add later:

Bibliography: LWW microbiology