IMViC Tests: Principle, Procedure and results

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 utilization test

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 are employed 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.

1. The positive result is indicated by the red layer at the top of the tube after the addition of Kovács reagent.
2. 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