Bile Esculin Azide Agar

 Principle

• Bile Esculin Azide Agar is a selective medium used for isolation and presumptive identification of fecal Streptococci. The composition and performance criteria of this medium are as per the specifications laid down in ISO 7899-1:1984.
• The media is composed of tryptone, meat peptone, yeast extract, oxgall, sodium chloride, esculin, ferric ammonium citrate, sodium azide, and agar. Tryptone and meat peptone provide nitrogen and other necessary minerals.
• Oxgall is a selective agent that inhibits gram-positive bacteria other than enterococci. Sodium chloride maintains osmatic equilibrium. Ferric citrate is an indicator of esculin hydrolysis.
• The esculin (glycoside) is the source of carbon. The esculin hydrolyzing microorganisms hydrolyzes esculin to esculetin and dextrose.
• The esculetin reacts with ferric citrate to form a brown or black color complex. Sodium azide inhibits most of the associated bacteria. Agar is the solidifying agent.
• The media is dispensed in tubes in the form of slants; a positive reaction is indicated by the blackening of more than half of the slant within 24-48 hours.
• If blackening is totally absent or if less than half of the slant is blackened within 24-48 hours, the test is negative. The media can be supplemented with 50ml/l horse serum, to enhance the growth of Enterococci.

Use:

Recommended for isolation and presumptive identification of fecal Streptococci.