Butyrate Disk Test: Principle, Procedure, Results and Uses

Principle: The butyrate disk is a rapid test for the detection of the enzyme butyrate esterase in identifying Moraxella (Branhamella ) catarrhalis. This test helps to differentiate Neisseria gonorrhoeae (negative) and Moraxella catarrhalis (positive), both are Oxidase positive, Gram negative diplococci.

If bromo-chloro-indolyl butyrate impregnated in the disks is hydrolyzed by the enzyme, a blue colored indigo compound is formed.

Procedure of Butyrate Disk Test

  1. Remove a disk from the vial and place on a glass microscope slide
  2. Add 1 drop of reagent grade water. This should leave a slight excess of water on the disk.
  3. Using a wooden applicator stick, rub a small amount of several colonies of Oxidase positive, Gram negative diplococci from an 18 to 24 hour pure culture on to the disk.
  4. Incubate at room temperature for up to 5 minutes.

Expected results:

  1. Positive: Development of a blue color during 5 minute incubation period.
  2. Negative: No color change

Quality control:

  1. Positive: Moraxella catarrhalis
  2. Negative: Neisseria gonorrhoeae