Blood Agar Base (Infusion Agar)

Intended Use
Blood Agar Base (Infusion Agar), with the addition of sterile blood, is used for the isolation, cultivation and detection of hemolytic activity of streptococci and other fastidious microorganisms.

User Quality Control
Identity Specifications
BBL™ Blood Agar Base (Infusion Agar)
Dehydrated Appearance: Fine, homogeneous, free of extraneous material.
Solution: 4.0% solution, soluble in purified water upon boiling. Solution is medium, yellow to tan, clear to slightly hazy.
Prepared Appearance: Plain – Medium, yellow to tan, clear to slightly hazy.
With 5% sheep blood – Cherry red, opaque.
Reaction of 4.0%
Solution at 25°C: pH 7.3 ± 0.2

Summary and Explanation
Infusion Agar is an all-purpose medium which has been used for many years as a base for the preparation of blood agars.
In a study of viability of streptococci, Snavely and Brahier performed comparative studies of horse, rabbit and sheep blood with Blood Agar Base, and found that sheep blood gave the clearest and most reliable colony and hemolysis characteristics
at both 24 and 48 hours.1 In the course of the investigation, about 1,300 isolations of streptococci were made with Blood Agar Base containing 5% sheep blood.
Blood Agar Base media are specified in standard methods for food testing. Infusion Agar has been largely replaced as a blood agar base by the Tryptic/Trypticase™ Soy Agar formulations, which contain milk and plant peptones in place of the variable
infusion component.

Principles of the Procedure
Infusion from heart muscle, casein peptone and yeast extract provide nitrogen, carbon, amino acids and vitamins in Blood Agar Base. Medium contains sodium chloride to maintain osmotic equilibrium and agar is the solidifying agent.
Supplementation with blood (5-10%) provides additional growth factors for fastidious microorganisms, and is the basis for determining hemolytic reactions. Hemolytic patterns may vary with the source of animal blood or type of base medium used.

Formula
BBL™ Blood Agar Base (Infusion Agar)
Approximate Formula* Per Liter
Heart Muscle, Infusion from (solids) : 2.0 g
Pancreatic Digest of Casein : 13.0 g
Yeast Extract : 5.0 g
Sodium Chloride : 5.0 g
Agar : 15.0 g
*Adjusted and/or supplemented as required to meet performance criteria.