Bile Esculin Azide Agar

Product information

For the selective isolation and differentiation of Group D streptococci

Bile Esculin Azide Agar is a modification of the medium reported by Isenberg and Isenberg, Goldberg, and Sampson. 1,2 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.
Molecular taxonomic studies of the genus Streptococcus have placed enterococci, previously described group D streptococci, in the genus Enterococcus.3 The ability to hydrolyze esculin in the presence of bile is a characteristic of enterococci and group D streptococci. Swan compared the use of an esculin medium containing 40% bile salts with the Lancefield serological method of grouping, and reported that a positive reaction on the bile esculin medium correlated with a serological group D precipitin reaction. 4 Facklam and Moody found that the bile esculin test provided a reliable means of identifying group D streptococci and differentiating them from non-group D streptococci.5
Sabbaj, Sutter, and Finegold evaluated selective media for selectivity, sensitivity, detection, and enumeration of presumptive group D streptococci from human feces. 6 Bile Esculin Azide Agar selected for S. bovis, displayed earlier distinctive reactions, and eliminated the requirement for special incubation temperatures.

Principles of the Procedure
Organisms positive for esculin hydrolysis hydrolyze the glycoside esculin to esculetin and dextrose. The esculetin reacts with the ferric citrate to form a dark brown or black complex. Oxbile is used to inhibit Gram-positive bacteria other enterococci, while Sodium Azide inhibits Gram-negative bacteria. Enzymatic Digest of Casein and Yeast Enriched Meat Peptone are the carbon, nitrogen, and vitamin sources used for general growth requirements in Bile Esculin Agar. Sodium Chloride maintains the osmotic balance of the medium. Sodium Citrate acts as a preservative. Agar is the solidifying agent.

Formula / Liter
Enzymatic Digest of Casein .........................................25g
Yeast Enriched Meat Peptone.....................................9.5g
Oxbile........................................................................1g
Sodium Chloride...........................................................5g
Sodium Citrate.............................................................1g
Ferric Ammonium Citrate.............................................0.5g
Esculin........................................................................1g
Sodium Azide..........................................................0.25g
Agar.........................................................................14g
Final pH: 7.1 ± 0.2 at 25°C
Formula may be adjusted and/or supplemented as required to meet performance specifications.