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Biology LibreTexts

36: Bile Esculin

Objectives

  • Identify the organism's ability to grow in high bile concentration and to use the sugar esculin

BILE ESCULIN

Bile esculin agar comes in a slant form. It is 2 tests in one---resistance to 40% bile AND the use of the sugar esculin.   Bile is a very inhibitory chemical, particularly at that concentration. IF the bacterium grows, the next question is whether it uses the esculin.

If your bacterium cannot grow in the presence of bile, the esculin reaction will have to be obtained a different way, using an esculin sugar disc

MATERIALS NEEDED

  • 1 bile esculin slant per unknown

THE PROCEDURE

  1. Using your unknown, streak the inoculum up the slant.
  2. Incubate the medium at 25º C or 37º C.

INTERPRETATION

  1. Growth on the slant = resistance to 40% bile 
  2. Use of esculin sugar = slant turns black coffee (over 1/2 of slant or entire agar) color

QUESTIONS

  1. The presence of growth on bile esculin means __________.
  2. What is esculin?  

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