About this test
What is the purpose of the test?
Bile salts are produced by the body to emulsify fats. Because of the nature of some bacterial cell walls, some bacteria are sensitive to bile salts and are killed. The purpose of the test is to determine if the unknown bacterium can grow on a medium containing bile salts .
How is growth on bile determined?
When streaked on a nutrient medium containing bile , microbes that can grow on bile will form abundant, visible growth.
What medium is used?
Usually, the medium used is bile esculin agar slant. This is a nutrient agar-based medium containing 10% bile salts and allowed to solidify at a slant. It contains the compound esculin, and the ability to use esculin is a second test use for this medium.
How is the test performed?
An inoculum from a pure culture is transferred aseptically to a sterile tube of bile esculin agar and streaked along the slant. There is no need to stab the medium. The inoculated tube is incubated at 35-37 C for 24 hours and the results are determined. Abundant growth on the slant indicates a positive test.
What reagents are added?
None.
Performing this test in the VUMIE Online lab
Inoculation of Medium
1. Select the is bile esculin agar slant. medium.
2. Using an inoculating wire, complete the process of a tube-to-tube aseptic transfer to inoculate the medium by streaking the slant and stabbing the butt of the medium. Forgotten how to do these things? Watch the “Show Me How To” videos.
Incubation of the Inoculated Medium
3. Place the inoculated tube into the 35-37 C incubator.
4. Press the New Day button to move forward 24 hours. Forgotten how to do these things? Watch the “Show Me How To” videos.
Determination of Test Results
5. Retrieve the incubated culture from the incubator.
6. Observe test result. If the test was followed as described above, those organisms able to grow in the presence of bile salts will produce abundant growth on the slant (a positive result). Negative tubes will have no growth on the slant.
7. Record test result.
Uninoculated Bile Esculin Agar Slant
Positive for Growth on Bile and Positive for Esculin Hydrolysis
Positive for Growth on Bile but Negative for Esculin Hydrolysis