Bile Esculin Agar
Bile esculin agar slants contain bile salts, esculin, ferric ammonium citrate, and beef and gelatin extracts. Organisms that are able to hydrolyze the carbohydrate esculin in the presence of bile will produce glucose and esculetin. The esculetin reacts with ferric ammonium citrate to form a blackish precipitate. The black precipitate must be in >50% of the tube to be considered positive.
Tube 1: Positive for esculin hydrolysis in the presence of bile. Note black precipitate in > 50% of tube.
Tube 2: Negative for esculin hydrolysis in the presence of bile.