Columbia Blood Agar Base

Specifications

Ingredients Gms / Litre :
Peptone, special 23.000
Corn starch 1.000
Sodium chloride 5.000
Agar 15.000
Final pH ( at 25°C)
**Formula adjusted, standardized to suit performance parameters
7.3±0.2

Principle & Interpretation :
Ellner et al (1) devised Columbia Blood Agar Base was devised. This medium contains special peptone which supports rapid and luxuriant growth of fastidious and non-fastidious organisms. Also, this medium promotes typical colonial morphology; better pigment production and more sharply defined haemolytic reactions. Fildes found that Nutrient Agar supplemented with a digest of sheep blood support the growth of H. influenzae (2, 3). The inclusion of bacitracin makes the enriched Columbia Agar Medium selective for the isolation of Haemophilus species from clinical specimens, especially from upper respiratory tract (4). Columbia Agar Base is used as base media containing blood and selective media formulations with different combinations of antimicrobial agents for isolation of different patriogons as reported in the literature.
Corn starch serves as an energy source and also neutralizes toxic metabolites. Sheep blood permits the detection of haemolysis and also provides heme (X factor) which is required for the growth of many bacteria. However it is devoid of V factor (Nicotinamide adenine dinucleotide) and hence Haemophilus influenzae which needs both the X and V factors, will not grow on this medium. As this me dium have a relatively high carbohydrate content, beta-haemolytic Streptococci may exhibit a greenish haemolytic reaction which may be mistaken for the alpha haemolysis. Columbia Agar Base with added sterile serum provides an efficient medium for Corynebacterium di phtheriae virulence test medium, and lines of toxin-antitoxin precipitation are clearly visible in 48 hours. Many pathogens require carbon dioxide; therefore, plates may be incubated in an atmosphere containing approximately 3-10% CO2.
Precaution: Brucella cultures are highly infective and must be handled carefully; incubate in 5-10% CO2. Campylobacter species are best grown at 42°C in a microaerophillic atmosphere. Plates with Gardenerella supplements plates should be incubated at 35°C for 4 8 hours containing 7% CO2 (5)