Aesculin - Aesculin Hydrolysis Test

Aesculin Hydrolysis Test

Aesculin is incorporated into agar with ferric citrate and bile salts (bile aesculin agar). Hydrolysis of the aesculin forms aesculetin (6,7-dihydroxycoumarin) and glucose. The 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 for 24 hours. The presence of a dark brown or black halo indicates that the test is positive. A positive test can occur with Enterococcus, Aerococcus and Leuconostoc. Aesculin will fluoresce under long wave ultraviolet light (360 nm): hydrolysis of aesculin results in loss of this fluorescence.

Enterococcus will often flag positive within four hours of the agar being inoculated.