streptococci

Streptococci
Streptococcus is a genus of spherical Gram-positive bacteria, Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs. Most streptococci are oxidase- and catalase-negative, and many are facultative anaerobes.
Classification of Streptococcus:-
Species of Streptococcus are classified based on their:-
1- Hemolytic properties:-
Alpha hemolytic species cause oxidization of iron in hemoglobin molecules within red blood cells, giving it a greenish color on blood agar. Beta hemolytic species cause complete rupture of red blood cells. On blood agar, this appears as wide areas clear of blood cells surrounding bacterial colonies. Gamma-hemolytic species cause no hemolysis.
Streptococci are further characterized via Lancefield serotyping, which describes specific carbohydrates present on the bacterial cell wall. There are 20 described serotypes, named Lancefield groups A to V (excluding I and J).
In the medical setting, the most important groups are: S. pyogenes (group A streptococci) and S. pneumoniae (pneumococci). Some of the other medically important streptococci are S agalactiae (group B), an etiologic agent of neonatal disease. S. mutans and S. sanguis (viridians streptococci) are responsible for the formation of dental plaque