Streptococcous

Streptococcous: د. زينب عادل چـابك
م. جوان أحمد علي الهماوندي
They are spherical, Gram-positive cocci arrange in long or short chain, also form pairs diplococcic (Streptococcus pnumoniae) lancet shape (head to head), due to cell division in one plane only. They are non-motile, non-spore forming, catalase negative (help to distinguish them from Staphylococcus). Some species are encapsulated.
Streptococcus species are widely distributed in nature. Some are members of the normal human flora mostly residents in mouth, throat and intestine, also may act as opportunistic pathogens and few species (Streptococcus pyogenes and Streptococcus agalactiae) as primary pathogens.

Classification:-
1- Serological grouping:
The most reliable classification of Streptococcus is Lancefield which classify Streptococcus in serological groups (A-H) (K-U) according to the cell wall antigenic polysaccharide and other capsular antigen
group A Streptococcus pyogenes
group B Streptococcus agalactiae
group D Enterococcus faecalis (previously called S.faecalis)
In Streptococcus pneumoniae , because it is surface carbohydrate antigens do not correspond to specific Lancefield group.

2- According to hemolytic activity on blood agar:
Alpha-hemolysis Streptococcus pneumoniae, viridance Streptococcus.
Beta-hemolysis Streptococcus pyogenes, Streptococcus agalactiae
Gamma-hemolysis Enterococcus faecalis