IMViC tests

The IMViC tests are a series of biochemical tests used in microbiology to differentiate among members of the Enterobacteriaceae family, particularly Escherichia coli and certain species of Enterobacter, Klebsiella, and Citrobacter. The name IMViC is an acronym derived from the initial letters of the four tests:

1. Indole Test (I): The indole test is used to detect the ability of an organism to produce indole from the amino acid tryptophan. The test is typically performed by inoculating a culture of the bacterium onto a medium containing tryptophan and a reagent such as Kovac's reagent. If the organism produces the enzyme tryptophanase, it will break down tryptophan to produce indole, which reacts with the reagent to form a red colour.

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3. Methyl Red Test (M): The methyl red test assesses the ability of an organism to perform mixed acid fermentation, a process that produces large amounts of acidic end products from glucose fermentation. The test involves inoculating the organism into a medium containing glucose and the pH indicator methyl red. After incubation, the medium is examined for the presence of stable acidic end products, indicated by a positive test (red colour).

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5. Voges-Proskauer Test (V): The Voges-Proskauer test detects the production of acetoin, a precursor to 2,3-butanediol, by organisms that ferment glucose. The test involves incubating the organism in a medium containing glucose and a reagent such as alpha-naphthol and potassium hydroxide. If the organism produces acetoin, it will react with the reagents to produce a red color, indicating a positive Voges-Proskauer test.

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7. Citrate Test (C): The citrate test assesses the ability of an organism to utilize citrate as its sole carbon source for growth. The test involves inoculating the organism onto a medium such as Simmons citrate agar, which contains citrate as the sole carbon source. If the organism possesses the enzyme citrate-permease, it will transport citrate into the cell, where it is converted to pyruvate and other intermediates, resulting in alkalization of the medium (change in color to blue), indicating a positive test.

These four tests are commonly used together to provide a biochemical profile that aids in the identification and differentiation of Enterobacteriaceae species, particularly within the genera Escherichia, Enterobacter, Klebsiella, and Citrobacter.