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
- Remove a disk from the vial and place on a glass microscope slide
- Add 1 drop of reagent grade water. This should leave a slight excess of water on the disk.
- 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.
- Incubate at room temperature for up to 5 minutes.
- Positive: Development of a blue color during 5 minute incubation period.
- Negative: No color change
- Positive: Moraxella catarrhalis
- Negative: Neisseria gonorrhoeae