Background
Moraxella catarrhalis, once thought to be non-pathogenic, is now considered a possible agent in respiratory infections.
Because this organism can be found at the same sites as pathogenic Neisseria spp. and shares some physiological and biochemical characteristics, it is important to have a screening test for differentiation of Moraxella catarrhalis (1,2).
Used in conjunction with other tests, Catarrhalis discs achieve this by demonstrating the enzymatic hydrolysis of bromo-chloro-indolyl butyrate which creates a blue reaction. Neisseria spp. do not hydrolyze this substrate and will remain colorless.
The test involves smearing a portion of a freshly cultured colony onto a moistened disc and observing the development of a bright blue colour within 5 to 15 minutes for a positive reaction.