|Cell Wall: Gram Positive||Shape: Cocci|
|Biochemistry: Catalase Negative||Metabolism: Microaerophilic|
- Both staphylococci and streptococci are gram positive cocci; therefore, it is important to understand how these organisms are differentiated. Additionally, it is important to appreciate how different strains of Streptococci are differentiated from one another.
- Differentiation From Staphylococci
- Gram Stain: Streptococci appear as strings of beads on gram stain whereas staphylococci appear as grape-like clusters
- Catalase: All streptococci are catalase negative, and thus do not bubble when exposed to hydrogen peroxide (H2O2).
- Differentiation Between Strains
- Hemolytic ability (Ability to lyse erythrocytes)
- Streptococci are plated on blood agar plate and area surrounding colonies are observed
- Beta-hemolytic: Completely hemolyze RBCs, white area surrounds colonies
- Alpha-hemolytic: Partially hemolyze RBCs, green area surrounds colonies
- Gamma-hemolytic: Cannot hemolyze RBCs, red area surrounds colonies.
- Antigenic characteristics
- Streptococci can be differentiated based on the antigenic characteristics of a carbohydrate in streptococcal cell wall. These Lancefield antigens are given letter names A, B, C, D, and so on. However, note that some strains do not have Lancefield antigens.