Columbia CNA w/ 5% Sheep Blood Agar

  1. Why is this test performed?
    Used as a undefined, differential, selective medium that allows isolation of Gram positive cocci. It inhibits growth of Gram negative.

    SELECTIVE: Colistin & Nalidixic Acid will not kill Streptococcus or Staphococcus organisms.

    DIFFERENTIAL: Hemolysis of RBC.
  2. How is the agar inoculated?
    Plate is divided into 4 sections. Spot inoculate each section with test organism.
  3. What special ingredients are added to agar to perform the test?
    Colistin & Nalidixid Acid & Sheep Blood.
  4. How can we tell the diff btwn pos & neg results? What do they tell us about the bacteria used?
    POSITIVE: If there's growth, then it is Gram + cocci. Not inhibited by colistin & nalidixic acid.

    • Alpha hemolysis (α): Partially hemolyzes RBC, produces a green discoloration of the medium.
    • Beta hemolysis (β): Completely hemolyzes RBC, producing a clear zone surrounding the colony.
    • Gamma hemolysis (γ): Doen NOT hemolyze RBC, there is no change in the medium.

    NEGATIVE: If no growth, then it's Gram -. (Inhibited by colistin & nalidixic acid.)
Card Set
Columbia CNA w/ 5% Sheep Blood Agar