In the MRVP test, which two reagents must be added to determine if the bacterium is VP positive?

In the MRVP test, which two reagents must be added to determine if the bacterium is VP positive?

• A. Creatine and 1N HCl
• B. 10% FeCl3 and alpha-naphthol
• C. Kovac's reagent and zinc dust
• D. Alpha-naphthol and 40% KOH

Answer: (D)

In the Voges-Proskauer portion of the MRVP test, acetoin production is detected using Barritt’s reagents: alpha-naphthol and potassium hydroxide. After incubation, add alpha-naphthol to the broth, then add 40% KOH. If acetoin is produced, it is oxidized in the alkaline environment to diacetyl, which reacts with guanidine in the medium to form a red complex—giving a VP-positive result. Alpha-naphthol acts as the color developer to speed and intensify this color change, while the alkaline KOH provides the conditions needed for diacetyl formation. If no red color appears, the test is VP negative.

In the Voges-Proskauer portion of the MRVP test, acetoin production is detected using Barritt’s reagents: alpha-naphthol and potassium hydroxide. After incubation, add alpha-naphthol to the broth, then add 40% KOH. If acetoin is produced, it is oxidized in the alkaline environment to diacetyl, which reacts with guanidine in the medium to form a red complex—giving a VP-positive result. Alpha-naphthol acts as the color developer to speed and intensify this color change, while the alkaline KOH provides the conditions needed for diacetyl formation. If no red color appears, the test is VP negative.