Aesculin, also called æsculin or esculin, is a coumarin

glucoside A glucoside is a glycoside that is derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is hydrolysed by purely chemical means, or decomposed by fermentation or enzymes. The name was o ...

that naturally occurs in the trees

horse chestnut The genus ''Aesculus'' ( or ), with species called buckeye and horse chestnut, comprises 13–19 species of flowering plants in the family Sapindaceae. They are trees and shrubs native to the temperate Northern Hemisphere, with six species n ...

(''Aesculus hippocastanum''),

California buckeye ''Aesculus californica'', commonly known as the California buckeye or California horse-chestnut, is a species of buckeye native to California and southwestern Oregon. Description It is a large deciduous shrub or small tree, up to tall, with ...

(''Aesculus californica''),

prickly box ''Bursaria spinosa'' is a small tree or shrub in the family Pittosporaceae. The species occurs mainly in the eastern and southern half of Australia and not in Western Australia and the Northern Territory. Reaching 10 m (35 ft) high, ...

(''Bursaria spinosa''), and

daphnin Daphnin is a plant toxin with the chemical formula C15H16O9 and is one of the active compounds present in the Eurasian and North African genus ''Daphne'' of the Thymelaeaceae The Thymelaeaceae are a cosmopolitan family of flowering plants comp ...

(the dark green resin of ''

Daphne mezereum ''Daphne mezereum'', commonly known as mezereum, mezereon, February daphne, spurge laurel or spurge olive, is a species of '' Daphne'' in the flowering plant family Thymelaeaceae, native to most of Europe and Western Asia, north to northern Scan ...

''). It is also found in

dandelion coffee Dandelion 'coffee' (also dandelion tea) is a tisane made from the root of the dandelion plant. The roasted dandelion root pieces and the beverage have some resemblance to coffee in appearance and taste, and it is thus commonly considered a coffee ...

Medical uses

As medication, aesculin is sometimes used as a vasoprotective agent. Aesculin is also used in a microbiology laboratory to aid in the identification of bacterial species (especially ''Enterococci'' and

Listeria ''Listeria'' is a genus of bacteria that acts as an intracellular parasite in mammals. Until 1992, 17 species were known, each containing two subspecies. By 2020, 21 species had been identified. The genus is named in honour of the British pi ...

Qadri, S. M., Smith, J. C., Zubairi, S., & DeSilva, M. I. (1981). Esculin hydrolysis by Gram positive bacteria. A rapid test and it's comparison with other methods. Medical microbiology and immunology, 169(2), 67–74. https://doi.org/10.1007/BF02171773 . PMID 6783825). In fact, all strains of Group D Streptococci hydrolyze æsculin in 40% bile.

Aesculin hydrolysis test

Aesculin is incorporated into agar with

ferric citrate Ferric citrate or iron(III) citrate describes any of several complexes formed upon binding any of the several conjugate bases derived from citric acid with ferric ions. Most of these complexes are orange or red-brown. They contain two or more Fe ...

and bile salts (

bile aesculin agar Bile Esculin Agar (BEA) is a selective differential agar used to isolate and identify members of the genus ''Enterococcus'', formerly part of the "group D streptococci" (enterococci were reclassified in their own genus in 1984). Composition and p ...

).National Standard Methods
MSOP 48 (Bile aesculin agar) and BSOPTP 2 (Aesculin hydrolysis test (UK))

Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of aesculin forms

aesculetin Aesculetin (also known as esculetin, 6,7-dihydroxycoumarin and cichorigenin) is a derivative of coumarin. It is a natural lactone that derives from the intramolecular cyclization of a cinnamic acid derivative. It is present in chicory and in many ...

(6,7-dihydroxycoumarin) and

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

. 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 ''Enterococcus'' is a large genus of lactic acid bacteria of the phylum Bacillota. Enterococci are gram-positive cocci that often occur in pairs (diplococci) or short chains, and are difficult to distinguish from streptococci on physical charact ...

'', ''

Aerococcus ''Aerococcus'' is a genus in the phylum Bacillota (Bacteria). The genus was first identified in 1953 from samples of air and dust as a catalase-negative, gram-positive coccus that grew in small clusters. They were subsequently found in hospital ...

'', and ''

Leuconostoc ''Leuconostoc'' is a genus of gram-positive bacteria, placed within the family of Lactobacillaceae. They are generally ovoid cocci often forming chains. ''Leuconostoc'' spp. are intrinsically resistant to vancomycin and are catalase-negative (wh ...

''. Aesculin will

fluoresce Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

under long wave

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

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. Esculine UV vis spectrum

Warnings

Aesculin ingestion can produce stomach ache, spasms, diarrhea, disorientation and even death at high doses.

References

{{coumarin Coumarin glycosides Microbiological media ingredients