Columbia Agar with 5% Sheep Blood- Composition, Principle, Preparation, Results, Uses


Columbia Agar with 5% Sheep Blood is a type of enriched and differential culture medium that is used for the isolation and identification of various bacteria from clinical specimens. It consists of a base medium (Columbia Agar) and an additive (Sheep Blood).

The base medium, Columbia Agar, contains the following ingredients:

  • Pancreatic digest of casein and enzymatic digest of animal tissue: These are peptones that provide nitrogen, carbon, vitamins, and trace elements necessary for the growth of bacteria.
  • Yeast extract: This is a source of vitamin B complex that enhances bacterial growth and metabolism.
  • Corn starch: This is a carbohydrate that serves as an energy source for bacteria and also neutralizes toxic metabolites by absorbing them.
  • Sodium chloride: This is a salt that maintains the osmotic balance and pH of the medium.
  • Agar: This is a solidifying agent that gives the medium a gel-like consistency.

The additive, Sheep Blood, is added to the base medium after sterilization. It has the following functions:

  • Hemolysis indicator: Sheep Blood contains red blood cells that can be lysed by some bacteria, producing different types of hemolysis (alpha, beta, or gamma) that can be observed on the medium. Hemolysis is a useful characteristic for identifying bacteria, especially streptococci and staphylococci.
  • X factor supplier: Sheep Blood also provides the X factor (heme) that is required for the growth of some bacteria, such as Haemophilus species. However, it does not provide the V factor (nicotinamide adenine dinucleotide, NAD) that is also needed by some Haemophilus species.

The final composition of Columbia Agar with 5% Sheep Blood (per liter) is as follows:

Ingredient Amount
Pancreatic digest of casein 23 g
Enzymatic digest of animal tissue 5 g
Yeast extract 5 g
Corn starch 1 g
Sodium chloride 5 g
Agar 15 g
Sheep blood 50 mL

The pH of the medium is adjusted to 7.3 ± 0.2 at 25°C before sterilization. The medium appears dark red in color after adding sheep blood.