Aesculin

 ( Coumarin Glycosides ) 

Aesculin, also called æsculin or esculin, is a coumarin glucoside that naturally occurs in the trees horse chestnut ( Aesculus hippocastanum), California buckeye ( Aesculus californica), C. Michael Hogan (2008) California Buckeye: Aesculus californica, GlobalTwitcher.com, N. Stromberg ed. and prickly box ( Bursaria spinosa). It is also found in daphnin (the dark green resin of Daphne mezereum), dandelion coffee, and Olea europaea 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.

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

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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 fluorescence under long wave ultraviolet light (360 nanometre) and hydrolysis of aesculin results in loss of this fluorescence.

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

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