Bile Esculin Test

Question 1

Purpose of bile esculin:

Answer 1

This test is used for the presumptive identifica tion of enterococci and organisms in n the Strep tococcus bovis group. The test differentiates enterococci and group D streptococci from non-group D viridans streptococci.

Question 2

Principle of bile esculin :

Answer 2

Gram-positive bacteria other than some strep tococci and enterococci are inhibited by the bile salts in this medium. Organisms capable of growth in the presence of 4% bile and able to hydrolyze esculin to esculetin. Esculetin reacts with Fe3+ and forms a dark brown to black precipitate.

Question 3

Bile esculin media made of:

Answer 3

Beef extract (11 g)
enzymatic digest of gelatin (34.5 g), esculin (1 g)
ox bile (2 g).
ferric ammonium citrate (0.5 g)
agar (15 g),
per 1000 mL
pH 6.6.

Question 4

Method of bile esculin:

Answer 4

1. Inoculate one to two colonies from an 18-to 24-hour culture onto the surface of the slant
2. Incubate at 35°-37°C in ambient air for 48 hours

Question 5

Expected results of bile esculin:

Answer 5

Positive: Growth and blackening of the agar slant
Negative: Growth and no blackening of medium -no growth ( not shown)

Question 6

Limitation of bile esculin:

Answer 6

As a result of nutritional requirements, some organisms may grow poorly or not at all on this medium.

Question 7

Quality control of bile esculin:

Answer 7

Positive: Enterococcus faecalis (ATCC19433)- growth, black precipitate

Negative: Escherichia coli (ATCC25922)- growth,no color change
Streptococcus pyogenes (ATCC19615)-по growth, no color change