Esculin (Aesculin) Hydrate
β-Glucosidase substrate for esculin hydrolysis tests and culture media
Esculin is a natural coumarin glycoside (6-β-D-glucoside of esculetin) used as the substrate in the esculin hydrolysis test, which detects bacterial β-glucosidase activity. It is the differential ingredient in Bile Esculin Agar, Oxford Agar, PALCAM and Fraser Broth. Esculin fluoresces blue under long-wave UV light, and loses this fluorescence when hydrolysed.
Also known as: Aesculin, esculoside, esculetin 6-glucoside, 6,7-dihydroxycoumarin 6-glucoside, 6-(β-D-glucopyranosyloxy)-7-hydroxycoumarin.
How the Esculin Hydrolysis Test Works
Bacteria that produce β-glucosidase (esculinase) split esculin into glucose and esculetin. Esculetin reacts with ferric ions, usually from ferric ammonium citrate, to form a dark brown to black complex around the colonies. Because intact esculin fluoresces blue under long-wave UV light (365 nm), hydrolysis can also be read as a loss of fluorescence.
Esculetin + Fe³⁺ gives a brown-black complex
Hydrolysed esculin no longer fluoresces at 365 nm
A positive result shows β-glucosidase activity
Culture Media That Contain Esculin
| Medium | Esculin (g/L) | Target organisms |
|---|---|---|
| Bile Esculin Agar | 1.0 | Enterococci and group D streptococci |
| Bile Esculin Azide Agar | 1.0 | Intestinal enterococci in water |
| Oxford Agar | 1.0 | Listeria spp. |
| PALCAM Agar | 0.8 | Listeria spp. |
| Fraser Broth / Half Fraser Broth | 1.0 | Listeria enrichment |
Typical Esculin Reactions
| Organism group | Esculin hydrolysis |
|---|---|
| Enterococcus spp., Streptococcus gallolyticus | Positive |
| Listeria spp. | Positive |
| Klebsiella, Enterobacter, Serratia (most strains) | Positive |
| Escherichia coli, Salmonella, Shigella | Negative |
| Streptococcus pyogenes | Negative |
Comparable Products
| Supplier | Product | Relationship |
|---|---|---|
| AuSaMicS | Esculin (Aesculin) Hydrate (ASC-8008) | — |
| Sigma-Aldrich (Merck) | Esculin hydrate (E8250) | Same substance, CAS 531-75-9 |
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Frequently Asked Questions
What is esculin used for in microbiology?
Esculin is the substrate for the esculin hydrolysis test. Bacteria with β-glucosidase split it into glucose and esculetin; with ferric ions, esculetin forms a brown-black complex. It is an ingredient of Bile Esculin Agar, Oxford Agar, PALCAM and Fraser Broth.
How much esculin is used in culture media?
Most media use 1.0 g/L esculin with 0.5 g/L ferric ammonium citrate or ferric citrate. Check the formulation of the specific medium.
How is esculin hydrolysis detected?
By blackening of the medium when iron is present, or by loss of esculin's blue fluorescence under long-wave UV light (365 nm). Both show that esculin has been hydrolysed.
Is esculin the same as aesculin?
Yes. Aesculin is the British spelling. Both names refer to 6-(β-D-glucopyranosyloxy)-7-hydroxycoumarin, CAS 531-75-9.
How should esculin be dissolved?
Esculin is only slightly soluble in cold water but dissolves readily in hot water. In media, add it with the other ingredients before heating.
Chemical Identity
Specifications
References
- MacFaddin JF. Biochemical Tests for Identification of Medical Bacteria. 3rd ed. Lippincott Williams & Wilkins; 2000. Esculin hydrolysis test.
- Edberg SC, Pittman S, Singer JM. Esculin hydrolysis by Enterobacteriaceae. J Clin Microbiol. 1977;6(2):111–116.
- Facklam RR, Moody MD. Presumptive identification of group D streptococci: the bile-esculin test. Appl Microbiol. 1970;20(2):245–250.
- Curtis GDW, Mitchell RG, King AF, Griffin EJ. A selective differential medium for the isolation of Listeria monocytogenes. Lett Appl Microbiol. 1989;8:95–98.
- National Center for Biotechnology Information. PubChem Compound Summary: Esculin (CID 5281417).
Current Lot
Safety
Not classified as hazardous under the GHS. Not Dangerous Goods for transport. Avoid breathing dust and wear gloves and eye protection when weighing. The full SDS is available for every lot.
Storage
Store at 15–25 °C, protected from light, with the container tightly closed. Keep dry. Re-test before use after the re-test date shown on the label.