Bile Esculin Agar (BEA) is a selective differential

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar is ...

used to isolate and identify members of the genus ''

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 ...

'', formerly part of the "group D streptococci" (enterococci were reclassified in their own

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

in 1984).

Composition and process

Bile salts are the selective ingredient, while

esculin Aesculin, also called æsculin or esculin, is a coumarin glucoside that naturally occurs in the trees Horse-chestnut (tree), horse chestnut (''Aesculus hippocastanum''), California buckeye (''Aesculus californica''), prickly box (''Bursaria spinos ...

is the differential component. ''

'' hydrolyze esculin to products that react with ferric citrate in the medium to produce insoluble iron salts, resulting in the blackening of the medium. Test results must be interpreted in conjunction with

gram stain In microbiology and bacteriology, Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. The name comes from the Danish ...

morphology.

Uses

Bile Esculin Agar is used primarily to differentiate ''

'' from ''

Streptococcus ''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs ...

''. Members of the genus ''

'' are capable of growing in the presence of 40% bile (oxgall) and hydrolyzing esculin to

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 ...

and

esculetin 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 ...

. Esculetin combines with ferric ions to produce a black complex. For some purposes, certain bacteria are able to hydrolyze

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''), prickly box (''Bursaria spinosa''), and daphnin (the ...

. A plate containing aesculin will fluoresce a pale blue under UV radiation. Some bacteria can hydrolise this, leading to UV dark colonies, as opposed to UV light ones. When new techniques are produced to identify enterococci, they are often compared to the use of bile esculin agar.

References

External links

Bile Esculin Agar Description & Formulation
{{Growth media Microbiological media