Aesculin
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Aesculin is a glucoside that naturally occurs in the horse chestnut Aesculus hippocastanum and in daphnin (the dark green resin of Daphne mezereum).
[edit] Medical uses
Aesculin is used in a microbiology laboratory to aid in the identification of bacterial species (especially Enterococci).
[edit] 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.
Streak the bile aesculin agar and incubate 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 (360nm): hydrolysis of aesculin results in loss of this fluorescence.
Enterococcus will often flag positive within four hours of the agar being inoculated.
[edit] References
- See National Standard Methods MSOP 48 (Bile aesculin agar) and BSOPTP 2 (Aesculin hydrolysis test).
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