A positive Voges-Proskauer reaction is characteristic of which organism among the following?

• A. Enterobacter aerogenes
• B. Escherichia coli
• C. Proteus vulgaris
• D. Providencia rettgeri

Answer: (A)

The Voges-Proskauer test detects whether a bacterium ferments glucose via the 2,3-butanediol (acetoin) pathway. Organisms that channel glucose into acetoin then convert it to detectible intermediates, when Barritt’s reagents are added, produce a red color, indicating a positive result. Enterobacter aerogenes uses the butanediol pathway and makes acetoin, so it gives a positive Voges-Proskauer reaction. In contrast, Escherichia coli typically ferments glucose through the mixed-acid pathway to stable acids rather than acetoin, so it is VP negative. Proteus vulgaris and Providencia rettgeri usually do not produce acetoin under standard testing conditions, and thus they are VP negative.