IMViC Tests

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 “C” is for citrate,  lowercase “i” is added for the ease of pronunciation. IMViC is an acronym that stands for four different tests

• Indole test
• Methyl red test
• Voges-Proskauer test
• Citrate test

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To obtain the results of these four tests, three test tubes are inoculated: tryptone broth (indole test), methyl red – Voges Proskauer broth (MR-VP broth), and citrate. IMViC tests areemployed in the identification/differentiation of members of family enterobacteriaceae.

General procedure for performing IMViC Tests and their interpretations:

Cultures of any members of enterobacteriaceae have to grow for 24 to 48 hours at 37°C and the respective tests can be performed:

Indole test

It is performed on sulfide-indole-motility (SIM) medium or in tryptophan broth, or in motility urease indole (MIU) medium. Result is read after adding Kovac’s reagent.

• The positive result is indicated by the red layer at the top of the tube after the addition of Kovács reagent.
• A negative result is indicated by the lack of color change at the top of the tube after the addition of Kovács reagent.

Methyl red test and Voges-Proskauer test both are done in methyl red–Voges-Proskauer (MR-VP) broth, but the reagents that are added varies according to the test

Methyl Red (MR)Test:

• Positive methyl red test are indicated by the development of red color after the addition of methyl red reagent.
• A negative methyl red test is indicated by no color change after the addition of methyl red reagent

Voges-Proskauer (VP) test:

1. Negative test is indicated by lack of color change after the addition of Barritt’s A and Barritt’s B reagents.
2. A positive Voges-Proskauer test is indicated by the development of red-brown color after the addition of Barritt’s A and Barritt’s B reagents.

 Citrate utilization test

The test is performed on Simmons citrate agar:

1. Negative citrate utilization test is indicated by the lack of growth and color change in the tube
2.  A positive citrate result as indicated by growth and a blue color change.

IMViC Test results of Some Genera of Enterobacteriaceae:       

1. IMViC tests of Escherichia coli
   1. Indole: Positive
   2. Methyl-Red: Positive
   3. Voges-Proskauer test: Negative
   4. Citrate test: Negative
2. IMViC tests of Enterobacter aerogenes
   1. Indole: Negative
   2. Methyl-Red: Negative
   3. Voges-Proskauer test: Positive
   4. Citrate test: Positive
3. IMViC tests of Proteus vulgaris
   1. Indole: Positive
   2. Methyl-Red: Positive
   3. Voges-Proskauer test: Negative
   4. Citrate test: Negative
4. IMViC tests of Citrobacter freundii
   1. Indole: Negative
   2. Methyl-Red: Positive
   3. Voges-Proskauer test: Negative
   4. Citrate test: Positive

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