IMViC Test- Principle, Result Chart, Examples, Uses


IMViC test is an acronym for four different biochemical tests that are used to identify and differentiate members of the Enterobacteriaceae family and other related bacteria. The four tests are:

  • Indole test: This test detects the ability of bacteria to produce indole from tryptophan, an amino acid. Indole is a chemical compound that has a characteristic smell and can be detected by adding a reagent such as Kovac`s or Ehrlich`s.
  • Methyl red (MR) test: This test detects the ability of bacteria to produce stable mixed acids from glucose fermentation. The pH of the medium is measured by adding methyl red indicator, which turns red at acidic pH and yellow at neutral or alkaline pH.
  • Voges-Proskauer (VP) test: This test detects the ability of bacteria to produce acetylmethylcarbinol (acetoin) from glucose fermentation. Acetoin is a neutral intermediate product that can be oxidized to diacetyl, which reacts with alpha-naphthol and potassium hydroxide to form a pink-red complex.
  • Citrate utilization test: This test detects the ability of bacteria to use citrate as a sole source of carbon and energy. The medium contains sodium citrate and bromothymol blue indicator, which changes color from green to blue when the pH increases due to citrate utilization.

The IMViC tests are performed on isolated pure cultures of bacteria that are grown on specific media. The results are interpreted by observing the color changes or the formation of rings or precipitates in the media or tubes. The results are usually reported as positive (+) or negative (-) for each test. For example, Escherichia coli is IMViC + + - -, meaning that it is positive for indole and methyl red tests, and negative for Voges-Proskauer and citrate utilization tests.

The IMViC tests are useful for characterizing and identifying bacteria up to the level of genus, and sometimes species. They are also helpful for distinguishing between closely related bacteria that have similar morphology and gram staining characteristics. For example, the indole test can differentiate between Klebsiella pneumoniae (-) and Klebsiella oxytoca (+), while the citrate utilization test can differentiate between Salmonella typhi (-) and Salmonella paratyphi A (+).

The IMViC tests are simple, inexpensive, and reliable methods for bacterial identification. However, they have some limitations, such as requiring pure cultures, long incubation periods, and additional tests for confirmation. Therefore, they are often used in combination with other biochemical, serological, or molecular methods for more accurate and comprehensive identification of bacteria.