Bile solubility test for Streptococcus pneumoniae


The bile solubility testing is microbiology biochemical test that helps to differentiate bile and bile salts soluble organism like Streptococcus pneumoniae from other insoluble bile and bile salt alpha haemolytic  streptococci such as streptococcus viridans.

Principle of Bile solubility test

  • Based on the emulsification of the suspected inoculum in normal saline and the addition of bile salt sodium deoxycholate.
  • bile salt sodium deoxycholate dissolves streptococcus pneumonia which is observed by a clearing of the turbidity with 10 -15 minutes.
  • Other non bile and bile salts soluble like streptococcus viridans and other streptococci are not dissolve therefore no clearing of turbidity

Material required for Bile solubility test

  • Sodium deoxycholate
  • Normal saline
  • Inoculum
  • 02 tube  (One for Control C while the other for test T)

Procedure of bile solubility test

  • Start by Emulsify several colonies of the test organism on a test tube containing about 2 ml normal saline in order to give a turbid suspension
  • Now transfer 1 ml of the emulsified colonies into 02 tubes
  • Label the Control tube as C while test tube as T contain 1 ml in each tube respectively
  • In Tube T add 2 drops of deoxycholate reagent and mix
  • Add 2 drops of normal saline in tube C and Mix
  • Incubate both tubes at 35-37 °C for a period of 10 – 15 minutes
  • Observe or look for clearing of turbidity in Tube T containing Sodium Deoxycholate


Clearing of Turbidity in tube TSoluble bile salt organism (Probably Streptococcus pneumoniae)
No clearing of Turbidity in Tube TInsoluble bile salt organism
Principle of Bile solubility test for Streptococcus pneumoniae

Note that Tube C is the control hence no reaction is supposed to occur in the tube.It is only used to compare Tube T because it only contain normal saline not test organism.

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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