Experiment 8: The IMViC Test

What is the IMViC test?

Tests for:

1. Indole production

2. Methyl red test

3. Vi = Voges-Proskauer rxn —> production of acetylmethylcarbinol

4. C —> use citrate as only Carbon source

What is the objectve of using the IMViC test?

separate and identify various types of coliform bacteria

What was this test used to differentiate between?

• E.coli —> + + - -

• K. aerogenes —> - - + +

What bacteria was used in this experiment?

• E. coli

• K. aerogenes

• C. freundii

What is the indole test?

• uses tryptone broth (rich in AA tryptophan)

• differentiates thos eorgs that can seperate the indole ring from tryptophan from those cant.

  • the ones with the separated indole ring have tryptophanase enzyme which catalyze hydrolysis of tryptophan to metabolic products, indole, pyruvic acid, ammonia.

• pyruvic acid, ammonia used by bacteria, indole ring is not used and stores in the medium

How to detect indole presence?

• using Kovac’s reagent

• if theres indole present (unused by the bacteria), a red ring forms.

What is the methyl red test?

• peptone water has 0.5% of glucose

• E.coli ferments the glucose to acidic products.

• others dont ferment as much acid as E.coli

• these bacteria get rid of the small glucose supply

• E. aerogenes converts organic acids to basic byproducts, raising the media’s pH

What does red and yellow mean for pH in the methyl red test?

red —> +ve, below 4.5 pH

yellow —> -ve, above 4.5

What is Voges-Proskauer reaction?

• detects when organic acids are broken down into nonacidic/neutral products.

• dererc acetylmethyl (acetoin) from sugar fermentation?

What reacts with Barritt’s reagent in the VP rxn?

• reacts with acetylmethylcarbinol, forming a pink complex that changes the colour of the medium.

What is the relationship between VP rxn and methyl red test?

• opposite complementary test to the methyl red test.

• If one is positive, the other should be negative

What is the citrate test?

• tests if organisms use citrate as a carbon source when glucose is unavailable.

What does a cell need to be able to use citrate as a carbon source?

citrate permease —> enzyme that allows cell to be processed by citrate.

What is the end product of the citrate test?

pyruvic acid and CO2 which creates an alkaline environment in the form of sodium carbonate

• turns green to deep blue.

What does a positive/negative Vi/VP test signify?

• positive = cherry red

• negative = brown