Question

Barritts reagent is used in ________.

• A. Indole test
• B. Methyl red test
• C. Eijkman's test
• D. Voges-Proskauer

Hint:

Remember the VP test color chemistry:
Acetoin $+$ $\text{KOH}$ (oxidizer) $\rightarrow$ Diacetyl.
Diacetyl $+$ peptone (guanidine) $+$ $\alpha$-naphthol (catalyst) $\rightarrow$ Cherry Red Complex.
Barritt's A = $\alpha$-naphthol; Barritt's B = $\text{KOH}$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The IMViC series of tests (Indole, Methyl Red, Voges-Proskauer, and Citrate) is a standard set of biochemical tests used to differentiate members of the family Enterobacteriaceae, particularly coliforms.
The Voges-Proskauer (VP) test specifically detects the production of acetoin (acetylmethylcarbinol), a neutral end-product of glucose fermentation.
Detailed Explanation:
Barritt's reagent is the indicator system used in the Voges-Proskauer test.
The reagent consists of two separate solutions:
- Barritt's A: $5\%$ $\alpha$-naphthol dissolved in absolute ethanol.
- Barritt's B: $40\%$ potassium hydroxide ($\text{KOH}$) in water.
During the VP test, bacteria are grown in MR-VP broth.
If the organism ferments glucose via the butylene glycol pathway, it produces acetoin.
Upon adding Barritt's reagent, the potassium hydroxide ($\text{KOH}$) in Barritt's B acts as an oxidizing agent, converting acetoin to diacetyl in the presence of atmospheric oxygen.
The diacetyl then reacts with guanidine group-containing compounds present in the peptone peptone broth.
The $\alpha$-naphthol in Barritt's A acts as a color catalyst and intensifier, producing a cherry-red color complex within 15 to 30 minutes, which indicates a positive test.
Let us review the reagents for the other tests:
- Indole test uses Kovac's reagent (p-dimethylaminobenzaldehyde).
- Methyl red test uses a simple methyl red pH indicator solution.
- Eijkman's test is a selective temperature-based fermentation test that does not use Barritt's reagent.

Step 2: Final Answer:
Barritt's reagent is used in the Voges-Proskauer test.