Description
Motility, indole production and ornithine decarboxylation are routine biochemical tests employed during identification of Enterobacteriaceae. Motility can be demonstrated microscopically (hanging drop) or macroscopically (tube method), where motility is observed as a diffused zone of growth flaring out from the line of inoculation. Indole test is carried out to determine the ability of an organism to split indole from tryptophan by the tryptophanase enzyme. On reaction with Kovacs reagent, indole combines with the colour in the alcohol layer, which is visualized as a red ring (in the alcohol layer). If the test organisms possess the specific decarboxylase enzyme, then ornithine is decarboxylated to putrescine, an amine, resulting in a subsequent rise in the pH of the medium towards alkalinity. This causes the pH indicator bromocresol purple to change from purple to yellow colour. MIO (Motility Indole Ornithine Medium) is used for identification of Enterobacteriaceae on the basis of motility, indole production and ornithine decarboxylation in a single tube. This medium was formulated by Ederer and Clark and evaluated by Oberhofer and Hajkowski.
