Butyrate Disk Test- Principle, Procedure, Results, Uses, Limitations


Butyrate disk test is a simple and rapid method for the identification of Moraxella catarrhalis, a Gram-negative, oxidase-positive diplococcus that causes various respiratory infections in humans. M. catarrhalis is also known for its ability to produce β-lactamase, an enzyme that confers resistance to penicillin and ampicillin. Therefore, it is important to distinguish M. catarrhalis from other similar organisms, such as Neisseria gonorrhoeae and Neisseria lactamica, which are butyrate-negative.

The butyrate disk test is based on the detection of butyrate esterase, an enzyme that hydrolyzes butyrate substrates such as bromochloro-indolyl butyrate or 4-methylumbelliferyl butyrate. The hydrolysis of these substrates results in the formation of color or fluorescence that can be easily observed within 5 minutes. The test can be performed on a glass slide, a petri dish, or a tube, using disks impregnated with the substrates. The test is highly specific and sensitive for M. catarrhalis and can be used as a presumptive identification tool along with other tests such as Gram stain, oxidase test, and morphology on blood agar plates.

The butyrate disk test is a convenient and inexpensive alternative to conventional tests that may require longer incubation times or more complex reagents. The test is also useful for the differentiation of M. catarrhalis from other Moraxella species, as well as Eikenella and Acinetobacter, which may also produce butyrate esterase but have different characteristics. However, the test has some limitations that need to be considered, such as the possibility of false-positive or false-negative results due to various factors such as inoculum size, incubation time, or substrate quality.

In this article, we will discuss the objectives, principle, procedure, results, uses, and limitations of the butyrate disk test in detail.