What is bile esculin agar used for?
This is a medium that is both selective and differential. It tests the ability of organisms to hydrolyze esculin in the presence of bile. It is commonly used to identify members of the genus Enterococcus (E faecalis and E.
What bacteria is bile-esculin positive?
The bile-esculin test is widely used to differentiate enterococci and group D streptococci, which are bile tolerant and can hydrolyze esculin to esculetin, from non-group D viridans group streptococci, which grow poorly on bile.
What is the significance of bile esculin agar in urine culture?
Bile esculin agar is a selective and differential medium which is used to presumptively identify enterococci and group D streptococci based on the ability of an organism to hydrolyze esculin.
What is the positive color reaction for bile-esculin test?
the presence of bile. The free esculetin reacts with ferric citrate in the medium to form a phenolic iron complex, which turns the agar slant dark brown to black. An agar slant that is more than half darkened after no more than 48 hours’ incubation is bile-esculin positive.
How does a bile Esculin work?
Esculin is a glucoside consisting of glucose and hydroxycoumarin linked together by an ester bond through oxygen. The bile esculin test selects organisms first on the basis of their ability to grow in a medium with 4% bile salts followed by the selection based on their ability to hydrolyze esculin.
What is the principle of bile esculin test?
Bile esculin test is based on the hydrolysis of esculin into glucose and esculetin (6, 7-dihydroxy-coumarin) by a micro-organism that produce an enzyme esculinase. Esculetin reacts with an iron salt (ferric citrate) in the medium to form a phenolic iron complex which produces a dark brown or black color.
What is the composition of bile esculin agar?
Composition of Bile Esculin Agar
| Ingredients | Gms/liter |
|---|---|
| Esculin | 1.00 |
| Bile salts | 40.0 |
| Ferric citrate | 0.50 |
| Agar | 15.00 |
What makes bile esculin media selective and differential?
Bile esculin agar is both selective and differential medium. The selective aspect of the bile esculin agar is sodium azide and oxagall which inhibit the growth of G- and most G+. The differential aspect of esculin agar is esculin which very few organisms can hydrolyze in the presence of bile.
Is Staphylococcus aureus bile esculin positive?
Some strains of Staphylococcus, Aerococcus and Listeria monocytogenes may grow in the presence of bile and hydrolyze esculin. There are a few streptococci that do not hydrolyze esculin but will grow in the presence of bile. Growth without blackening of this medium does not constitute a positive test.
How do you perform a bile esculin agar test?
A. Tube Test
- Using sterile loop, pick one or two colonies from an 18-24 hours culture.
- Inoculate onto the surface of slant of bile esculin medium with an S-shaped motion.
- Incubate the inoculated tube at 35-37°C for 24 hours.
- Observe the result.
Is bile Esculin enriched?
Bacteroides Bile Esculin (BBE) agar is an enriched, selective, and differential medium used for the isolation and presumptive identification of obligately anaerobic gram-negative bacilli of the Bacteroides fragilis group and Bilophila wadsworthia.
How does Esculin hydrolysis work?
Principle of Esculin Hydrolysis Test The compound can be enzymatically hydrolyzed at the 8-glucose linkage to yield two products, esculetin, and glucose. Esculetin combines with ferric ions, generally incorporated in the medium as ferric ammonium citrate, to produce a brown-black colored compound.