Aesculin

Aesculin, also called æsculin or esculin, is a coumarin glucoside that naturally occurs in the trees horse chestnut (''Aesculus hippocastanum''), California buckeye (''Aesculus californica''), and prickly box (''Bursaria spinosa''). It is also found in daphnin (the dark green resin of '' Daphne mezereum''), dandelion coffee, and olive bark. It is reported to be present in olive bark, but not in olive leaf; therefore, identification of aesculin in abundance in an olive extract indicates that the extract has been derived from olive bark.

Uses

Aesculin is also used in a microbiology laboratory to aid in the identification of bacterial species (especially ''Enterococci'' and Listeria). In fact, all strains of Group D Streptococci hydrolyze aesculin in 40% bile.

Aesculin hydrolysis test

Aesculin is incorporated into agar with ferric citrate and bile salts ( bile aesculin agar).National Standard Methods
MSOP 48 (Bile aesculin agar) and BSOPTP 2 (Aesculin hydrolysis test (UK)) Hydrolysis of aesculin forms aesculetin (6,7-dihydroxycoumarin) and glucose. 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 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) and hydrolysis of aesculin results in loss of this fluorescence.

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

References

{{coumarin

Coumarin glycosides
Microbiological media ingredients