Result: Change in color from red to yellow-orange indicates carbohydrate utilization.
BILE SOLUBILITY TEST
This helps to differentate S.pneumoniae, which is soluble in bile and bile salts, from viridans streptococci which are insoluble.
A heavy inoculum of the test organism is emulsified in physiological saline to give a turbid suspension. The bile salt sodium deoxycholate is then added. The test can also be performed by adding the bile salt to a broth culture of the organism. The bile salt dissoles S.pneumoniae as shown by a clearing of the turbidity within 10-15 minutes. Viridans streptococci are not dissolved and therefore there is no clearing of the turbidity.
Sodium deochollate100g/l Physiological saline (sodium chloride, 8.5g/l) Method
Emulsify several colonies of the test organism in a tube containing 2ml of sterile physiological saline, to give a turbid suspension.
Divide the organism suspension between two tubes.
To one tube, add 2 drops of the sodium deoxycholate reagent and mix.