Aesculetin forms dark brown or black complexes with ferric citrate, allowing the test to be read. The bile aesculin agar is streaked and incubated at 37 °C (99 °F) for 24 hours. ... Aesculin will fluoresce under long wave ultraviolet light (360 nm) and hydrolysis of aesculin results in loss of this fluorescence.

How does Aesculin agar work?

Aesculetin combines with ferric citrate in the medium to form a dark brown or black complex which is indicative of a positive result. Bile salts will inhibit Gram-positive bacteria other than enterococci / Group D streptococci.

What is the principle of bile esculin test?

Bile esculin test is based on the hydrolysis of esculin into glucose and esculetin (6, 7-dihydroxy-coumarin) by a micro-organism that produce an enzyme esculinase. Esculetin reacts with an iron salt (ferric citrate) in the medium to form a phenolic iron complex which produces a dark brown or black color.