Question

10. IMViC stands for what tests? What results are expected for E. coli and Enterobacter aerogenes? What reagent(s)-indicator(s) give the reactions? How do positive tests look?

Answer 1

IMViC stands for four different tests. Indole test. Methyl red test. Voges-Proskauer test. Citrate utilization test.

Indole test is performed on sulfide-indole-motility (SIM) medium or in tryptophan broth, or in motility urease indole (MIU) medium. The positive result is indicated by the red layer 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 varies according to the test.

Methyl red test: methyl red reagent is added and positive result is indicated by appearance of red color and negative is indicated by no color change.

Voges-Proskauer test: Reagents are Barritt’s A and Barritt’s B reagents. After addition of reagents, development of red brown color indicates positive and no change in color is negative in result.

Citrate utilization test is performed on Simmons citrate agar. Positive result indicated by a blue color change and growth of cells. While negative color change indicated by no chnage in color and growth.

IMViC tests of Escherichia coli

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

IMViC tests of Enterobacter aerogenes

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