Microbiology Lab Practice Exam 2026 - Free Microbiology Practice Questions and Study Guide

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In VP test interpretation, what does a positive result indicate about acetoin production?

Gas production indicates acetoin production.

Acetoin is detected by the Moraxella oxidation test.

Acetoin production from glucose fermentation is detected by the VP test.

The Voges-Proskauer test is designed to detect acetoin, a metabolite produced when some bacteria ferment glucose via the 2,3-butanediol pathway. After incubation, Barritt reagents react with acetoin to form diacetyl, which then interacts with compounds in the medium to give a red color. A positive result, indicated by the red color, means acetoin was produced during fermentation. Gas production is not what this test measures, and the Moraxella oxidation test is a different assay used for other purposes, not for acetoin detection. So, a positive VP result specifically indicates acetoin production from glucose fermentation.

Acetoin production is irrelevant to VP results.