The Vouges-Proskauer test indicates the presence of acetylmethylcarbinol (or acetoin) after glucose fermentation. For a span of 48-72 hours, the culture is grown in the same media as the methyl red test. After the completion of growth, a solution of alpha-naphthol is added followed by the base potassium hydroxide. Acetoin would then form a complex with the naphthol producing a color red in the media. Media with no acetoin present will be yellow.
Image 4. A negative Vouges Proskauer test on the left and a positive VP test on the right.
• The culture was the color yellow o The results of the Vouges-Proskaur test for the unknown bacteria were negative
4. Citrate Test
The Citrate Test indicates whether or not the bacteria contain the enzyme citrate permease, which is needed to bring citrate into the cell. The media used contains the pH indicator bromothymol blue which is green at a neutral pH level and blue at alkaline pH levels. If the top of the citrate slant has turned from green to blue, the culture is positive for citrate degradation producing alkaline byproducts. If not, the results are negative.
Image 5. A negative Citrate test on the left and a positive result on the right.
• The citrate slant remained green throughout the growth process o The results of the Citrate test for the unknown bacteria were negative
The Triple Sugar Iron slants are used to differentiate the Salmonella-Shigella group of