Streptococci

Streptococci
Introduction:
The streptococci are gram-positive spherical bacteria that characteristically form pairs or chains during growth. They are widely distributed in nature. Some are members of the normal human flora; others are associated with important human diseases.
Classification of Streptococci……
The classification of streptococci into major categories has been based on :
(1)colony morphology and hemolytic reactions on blood agar;
(2) serologic specificity of the cell wall group-specific substance and other cell wall or capsular antigens; There are 20 described serotypes, named Lancefield groups A to V (excluding I and J).
(3) biochemical reactions and resistance to physical and chemical factors.
(4) ecologic features.
Lab Diagnostic Test:
1-Gram stain: G + ve coccoid.
2- Bile solubility: In presence of bile salts (Na-deoxycholate or Na-taurocholate), the surface tension of this salts cause releasing of autolytic enzyme cause lysis of the cells.
(+) of this test is cell lysis (No growth)
(- ) of this test is growth of cells
3- Blood Agar: For the type of hemolysis.