Which reagent is added to test for the production of indole?

Which reagent is added to test for the production of indole?

• A. Bromcresol purple
• B. p-Dimethylaminobenzaldehyde
• C. Cytochrome oxidase
• D. Methyl red

Answer: (A)

The appropriate reagent used to test for the production of indole is p-Dimethylaminobenzaldehyde. This reagent reacts with indole, which is produced from the metabolism of the amino acid tryptophan by certain bacteria, resulting in the formation of a red or pink-colored compound. This color change indicates a positive result for indole production. When testing for indole, specific bacteria are inoculated into a medium containing tryptophan. After incubation, the addition of p-Dimethylaminobenzaldehyde allows for the visualization of indole presence. The lack of color change indicates that the organism does not produce indole, affirming its non-tryptophanase activity. While bromcresol purple is used in other contexts, such as pH indicator tests, and methyl red is used to test for mixed acid fermentation, they do not assess indole production. Cytochrome oxidase is another test used to determine the presence of cytochrome c oxidase in bacteria and is unrelated to indole testing. Thus, the accurate identification of indole using p-Dimethylaminobenzaldehyde is central to differentiating specific Enterobacteriaceae species.

The appropriate reagent used to test for the production of indole is p-Dimethylaminobenzaldehyde. This reagent reacts with indole, which is produced from the metabolism of the amino acid tryptophan by certain bacteria, resulting in the formation of a red or pink-colored compound. This color change indicates a positive result for indole production.

When testing for indole, specific bacteria are inoculated into a medium containing tryptophan. After incubation, the addition of p-Dimethylaminobenzaldehyde allows for the visualization of indole presence. The lack of color change indicates that the organism does not produce indole, affirming its non-tryptophanase activity.

While bromcresol purple is used in other contexts, such as pH indicator tests, and methyl red is used to test for mixed acid fermentation, they do not assess indole production. Cytochrome oxidase is another test used to determine the presence of cytochrome c oxidase in bacteria and is unrelated to indole testing. Thus, the accurate identification of indole using p-Dimethylaminobenzaldehyde is central to differentiating specific Enterobacteriaceae species.