What is the role of the sodium azide in bile-esculin azide agar media?

What is the role of the sodium azide in bile-esculin azide agar media?

Sodium azide and 1% Oxgall (equivalent to 10% bile) are selective agents added to inhibit gram-negative bacilli and most gram-positive bacteria other than group D streptococci and enterococci.

What is the purpose of bile-esculin test?

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 causes the color change in bile-esculin?

After the degradation of esculin, the esculetin produced by the hydrolysis of esculin reacts with iron ions (from ferric citrate) in the medium to form a phenolic iron complex, resulting in a dark brown or black color.

Which of the components gives bile-esculin media its selective properties Why?

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.

What is the purpose of using bile esculin agar with vancomycin?

INTENDED USE Remel Bile Esculin Azide Agar w/ 6 µg/ml Vancomycin is a solid medium recommended for use in qualitative procedures as a screening method for primary isolation and presumptive identification of vancomycin-resistant enterococci (VRE) from surveillance cultures.

What is the substrate in bile esculin agar?

p-Nitrophenyl-beta-D-glucopyranoside was the esculinase substrate, and sodium desoxycholate was substituted for bile salts. After inoculation, a yellow color was equivalent to the brown-black seen in the 40% bile-esculin reaction.

What is the indicator for bile esculin test?

Bile esculin medium contains esculin and peptone for nutrition and bile to inhibit Gram-positive bacteria other than Group D streptococci and enterococci. Ferric citrate is added as a color indicator.

Which of the following describes the bile esculin agar?

faecalis and other Enterococcus species because only E. faecalis can metabolize the glucose in the Esculin to create Esculetin. Explain how bile esculin agar acts as a selective medium, including the ingredients in the media that are selective. Selective ingredient: Oxgall & Sodium Azide.

What are the nutrients in bile esculin agar?

The constituents of bile-esculin agar medium are peptone, beef extract, oxgall (bile), esculin, ferric citrate, and agar. Bile esculin medium contains esculin and peptone for nutrition and bile to inhibit Gram-positive bacteria other than Group D streptococci and enterococci.

Is bile esculin agar defined?

Which group of bacteria does the Bile Esculin test help to identify? Bile Esculin agar is a defined medium or an undefined medium? UNdefined bc the amino acid source contains a variety of compounds with the exact composition being unknown.

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 do you perform a bile esculin agar test?

A. Tube Test

1. Using sterile loop, pick one or two colonies from an 18-24 hours culture.
2. Inoculate onto the surface of slant of bile esculin medium with an S-shaped motion.
3. Incubate the inoculated tube at 35-37°C for 24 hours.
4. Observe the result.

What is the bile esculin test used for?

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 happens when esculin hydrolyzed in the presence of bile?

If an organism can hydrolyze esculin in the presence of bile, the product esculetin is formed. Esculetin reacts with ferric citrate (in the medium), forming a phenolic iron complex which turns the entire slant dark brown to black. The tube on the far right was inoculated with E. faecalis (positive).

What is the composition of Bile Esculin Agar?

Bile esculin agar contains oxgall (bile salts) to inhibit the growth of gram positive organisms other than enterococci and group D streptococci. It also contains nutrients, esculin, and ferric citrate. When an organism hydrolyzes the glycoside esculin to form esculetin and dextrose, the esculetin reacts with the ferric citrate to produce…

What is esculin hydrolysis test used for?

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. faecium ).