For isolation and presumptive identification of faecal streptococci. (ISO 7899-2 : 2000). Bile Esculin Azide Agar is a modification of Bile Esculin Agar developed by Isenberg and recommended as a selective and highly nutritive medium for Streptococci. This formula modifies Bile Esculin Agar by adding sodium azide and reducing the concentration of bile. The revised medium is more selective, but still provides rapid growth and efficient recovery of group D streptococci. Bile Esculin Azide Agar contains casein enzymatic hydrolysate, peptic digest of animal tissue and beef extract which supply the essential nutrients for Streptoococci like e.g. amino acids, other nitrogenous and carbonaceous compounds. Sodium chloride maintains the osmotic equilibrium of the medium. The inclusion of esculin allows for detection of esculin hydrolysis by the bacterial enzyme, esculinase. Esculin hydrolysis liberates esculetin which in turn reacts with ferric citrate in the medium to produce black phenolic iron-complex giving esculinase-positive colonies a brown-black halo. Selectivity is accomplished by the addition of oxgall and sodium azide. Oxgall inhibits the growth of most gram-positive cocci other than Enterococci and group D Streptococci, while sodium azide inhibits gram-negative bacteria that may be contained in some clinical samples and agar is the solidifying agent.