What is the purpose of the test? This test determines whether the microbe performs mixed acids fermentation when supplied glucose . Mixed acids fermentation results in accumulation of a variety of acids and a significant drop in the pH of the medium.
How is the mixed acids fermentation determined? If the microbe performs mixed acids fermentation , the medium will acquire an acidic pH. Addition of a pH indicator which changes color below pH 4 indicates presence of the extreme acidity associated with mixed acids fermentation.
What medium is used? The medium used is MRVP broth, a nutrient medium with 0.5% glucose added. This medium is also used for the Voges-Proskauer test, which determines whether neutral fermentation products result from growth.
How is the test performed? An inoculum from a pure culture is transferred aseptically to a sterile tube of MRVP broth. The inoculated tube is incubated at 35-37 C for 24 hours.
What reagents are added? After incubation, five drops of methyl red are added. It is a pH indicator which is yellow at neutral pH but turns red at pH <4.0. Mixed acids fermentation results in a red color change.
To perform this test in VUMIE Online© Online Lab , complete the following steps:
Inoculation of Medium
1. Select the MRVP broth medium.
2. Complete the process of a tube-to-tube aseptic transfer to inoculate the medium. Forgotten how to do these things? Watch the "Show Me How To" videos.
Incubation of the Inoculated Medium
3. Place the inoculated tube into the 35-37 C incubator.
4. Press the New Day button to move forward 24 hours. Forgotten how to do these things? Watch the "Show Me How To" videos.
Addition of Reagents
5. Incubate this test for only 24 hours.
6. Retrieve the incubated culture from the incubator.
7. This is a test that requires addition of reagents to bring about the change in appearance of a positive test.
Select the dropper tool and the appropriate reagent needed from the chemical shelf. For this test, select Methyl Red reagent. Remove the cap lid and add the reagent.
Determination of Test Results
8. Observe test result. For this test, addition of the appropriate reagent makes the culture turn red if the test is positive. If negative, no color change is observed.
9. Record test result.