A test for hydrolysis of esculin in the presence of bile is especially useful in identifying species of which genus?

• A. Abiotrophia
• B. Corynebacterium
• C. Enterococcus
• D. Staphylococcus

Answer: (C)

Hydrolysis of esculin in the presence of bile is used to identify organisms that can tolerate bile and enzymatically break down esculin. When esculin is hydrolyzed, esculetin reacts with ferric ions in the medium to form a dark, brown‑black complex around the colonies. Enterococcus species are notable for growing in bile and rapidly hydrolyzing esculin even with bile present, so a positive bile esculin test strongly points to this genus. The other organisms listed do not characteristically show this reaction in bile, so they are less likely to yield a positive result. Therefore, a bile esculin–positive test best identifies Enterococcus.