The IMViC tests are a group of individual tests used in microbiology lab testing to identify an organism in the coliform group. A coliform is a gram negative, aerobic or facultative anaerobic rod which produces gas from lactose within 48 hours. The presence of some coliforms indicate fecal contamination.
Except for the lowercase “i”, which is added for ease of pronunciation, each of the letters in “IMViC” stands for one of these tests. “I” is for indole; “M” is for methyl red; “V” is for Voges-Proskauer, and “iC” is for citrate.
In this test, the organism under consideration is grown in peptone Water Broth. It contains tryptophan, which under the action of enzyme tryptophanase is converted to an Indole molecule, pyruvate and carbon dioxide.The indole is then extracted from the broth by means of xylene. To test the broth for indole production, Kovac's reagent is added. A positive result is indicated by a Pink/Red layer forming on top of the liquid.
These tests both use the same broth for bacterial growth. The broth is called MRVP broth. After growth, the broth is separated into two different tubes, one for the Methyl Red (MR) test and one for the Voges-Proskauer (VP) test. The pH indicator Methyl Red is added to one tube and a red color appears at pH's lower than 4.2, and indicated positive test. The VP test uses alpha-naphthol and potassium hydroxide to indicate a positive or negative test.
This test uses Simmon's citrate agar to determine the ability of a microorganism to use citrate as its sole carbon source. The citrate agar is green before inoculation, and turns blue as a positive test indicator.
These IMViC tests are useful for differentiating the family Enterobacteriaceae, especially when used alongside the Urease test.