IMViC Tests: Principle, Procedure, Results

Each letter 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 ease of pronunciation. IMViC is an acronym that stands for four different tests

• Indole test
• Methyl red (MR) test
• Voges-Proskauer (VP) test
• Citrate utilization test

Three test tubes are inoculated to obtain the results of these four tests: 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 the 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 motility urease indole (MIU) medium. The 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 and Voges-Proskauer tests are done in methyl red–Voges-Proskauer (MR-VP) broth, but the added reagents vary according to the tests.

Methyl Red (MR) test

• Positive methyl red test is 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 VP test is indicated by a 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 is indicated by growth and a blue color change. 

IMViC Test results of some genera of Enterobacteriaceae:       

IMViC tests of Escherichia coli

• Indole: Positive
• Methyl-Red: Positive
• Voges-Proskauer test: Negative
• Citrate test: Negative

IMViC tests of Klebsiella (formerly Enterobacter) aerogenes

1. Indole: Negative
2. Methyl-Red: Negative
3. Voges-Proskauer test: Positive
4. Citrate test: Positive

IMViC tests of Proteus vulgaris

1. Indole: Positive
2. Methyl-Red: Positive
3. Voges-Proskauer test: Negative
4. Citrate test: Negative

IMViC tests of Citrobacter freundii

1. Indole: Negative
2. Methyl-Red: Positive
3. Voges-Proskauer test: Negative
4. Citrate test: Positive

References

1. Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). Brock Biology of Microorganisms (15th Edition). Pearson.
2. Pelczar Jr., M., Chan, E., & Krieg, N. (2007). Microbiology (5th edition). Tata McGraw-Hill
3. Bailey & Scott’s Diagnostic Microbiology, Forbes, 11th edition