Download Bile Esculin Test

Bile Esculin (WINTER 2014 version)
Introduction
Bile Esculin is a selective and a differential medium. It contains bile (which inhibits Gram-positive
staphylococci) and sodium azide (which inhibits Gram-negative bacteria). It contains esculin and peptone as
nutrient sources and ferric citrate as a color indicator.
Esculin is a carbohydrate linked to an alcohol. Many organisms can hydrolyze esculin but very few can do so in
the presence of bile. Organisms that do metabolize esculin produce esculetin as a by-product. Esculetin reacts
with ferric citrate to form a dark (black) coloration.
Results
+ = Positive (Any blackening of the agar within 72 hours)
- = Negative (No blackening of the agar within 72 hours)
CAUTION: This test should be incubated no more than 72 hours.
Methods
1. Obtain two Bile Esculin (BE) agar slants from the back shelf.
2. Inoculate one BE slant using aseptic technique (inoculate only the slanted surface). Leave the other BE
slant uninoculated (this will be a negative control).
3. Incubate at the appropriate temperature (whatever temperature your organism grows well at). Incubate
for 24 to 48 hours (do not exceed 72 hours for this test).
4. Obtain your BE slants from the incubator and observe the color in the photograph below.
Photograph