Cell Wall: Gram Positive Shape: Cocci
Biochemistry: Catalase Negative Metabolism: Microaerophilic
  • Overview
    • 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.
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