Bile esculin agar
{{Short description|Selective and differential culture medium}}
{{More citations needed|date=August 2023}}
Bile Esculin Agar (BEA) is a selective differential agar used to isolate and identify members of the genus Enterococcus,{{cite web |url=http://www.life.umd.edu/classroom/bsci424/LabMaterialsMethods/BSCI424Media.htm |title=BSCI424 Laboratory Media |access-date=2008-11-18|first=David M.|last=Rollins|date=2000|publisher=University of Maryland}} formerly part of the "group D streptococci" (enterococci were reclassified in their own genus in 1984).{{cite journal |vauthors=Lindell SS, Quinn P |title=Use of bile-esculin agar for rapid differentiation of Enterobacteriaceae |journal=J. Clin. Microbiol. |volume=1 |issue=5 |pages=440–3 |date=May 1975 |doi=10.1128/jcm.1.5.440-443.1975 |pmid=1176613 |pmc=275140 |url=}}
Composition and process
File:Bile esculin agar.jpg colonies (black) growing on BEA]]
Bile salts are the selective ingredient, while esculin is the differential component. Enterococcus 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 morphology.
Uses
Bile Esculin Agar is used primarily to differentiate Enterococcus from Streptococcus. Members of the genus Enterococcus are capable of growing in the presence of 40% bile (oxgall) and hydrolyzing esculin to glucose and esculetin. Esculetin combines with ferric ions to produce a black complex.
For some purposes, certain bacteria are able to hydrolyze aesculin. A plate containing aesculin will fluoresce a pale blue under UV radiation. Some bacteria can hydrolyze 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.{{cite journal |vauthors=Grabsch EA, Ghaly-Derias S, Gao W, Howden BP |title=Comparative study of selective chromogenic (chromID VRE) and bile esculin agars for isolation and identification of vanB-containing vancomycin-resistant enterococci from feces and rectal swabs |journal=J. Clin. Microbiol. |volume=46 |issue=12 |pages=4034–6 |date=December 2008 |pmid=18832121 |doi=10.1128/JCM.00944-08 |pmc=2593271}}
References
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External links
- [http://www.microbeid.com/Media/bileesculin.html Bile Esculin Agar Description & Formulation]
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