For selective isolation of fastidious pathogenic microorganisms after addition of blood.
BLOOD AGAR BASE (INFUSION AGAR) is used for isolation, cultivation of fastidious pathogenic microorganisms after addition of blood. Blood Agar Base media can be used as general-purpose media also, without blood addition. Blood agar base medium can also be used for primary isolation of Haemophilusspecies, where defibrinated sheep blood is used to enrich the medium. The medium contains a rich nutrient base, which provides optimal growth conditions for all relevant microorganisms. Tryptone and Brain Heartinfusion supply amino acids, minerals and other essential growth factors in the medium for the growth of microorganisms. Sodium chloride maintains the osmotic balance of the medium. Agar is a solidifying agent. On addition of blood, the pH value of 6.8 stabilizes and favors the formation of clear hemolysis zones. Fresh, defibrinated sheep blood is most suitable for determent hemolysis forms. It gives best results for Group A Streptococci. But sheep blood fails to support the growth of Haemophilus haemolyticus due to deficiency of pyridine nucleotides. However, the addition of horse blood supports H. haemolyticus growth and hemolysis and the growing colonies mimic Streptococcus pyogenes.