Streptococci

Streptococci

Characters of Streptococci. Gram +ve cocci, Chains or pairs
Usually capsulated, Non motile. Non spore forming
Facultative anaerobes, Fastidious, Catalase negative(Staphylococci are catalase positive).

Streptococci can be classified according to:
Serology (Lancefield Classification)
Hemolysis on Blood Agar (BA).

Serology: Lancefield Classification:
Streptococci classified into many groups from A-K & H-V
Classification based on C- carbohydrate antigen of cell wall
Groupable streptococci
A, B and D (more frequent)
C, G and F (Less frequent)
Non-groupable streptococci
S. pneumoniae (pneumonia)
viridans streptococci
e.g. S. mutans; Causing dental carries.

Classification Based on Hemolysis on Blood Agar:
Hemolysis on BA
?-hemolysis
Partial hemolysis
Green discoloration around the colonies
e.g. non-groupable streptococci (S. pneumoniae & S. viridans)
?-hemolysis
Complete hemolysis
Clear zone of hemolysis around the colonies
e.g. Group A & B (S. pyogenes & S. agalactiae)
?-hemolysis
No lysis
e.g. Group D (Enterococcus spp)