The MR-VP medium, short for methyl red and voges-proskauer, contains a large amount of dextrose. Many microbes, especially coliforms, convert a portion of the dextrose to acid. Other microbes may utilize the dextrose, but yield neutral end product like those formed in butanediol fermentation. Still yet, others may leave the dextrose unaltered. Once an unknown bacterium is isolated and diluted in liquified agar, methyl red and voges-proskauer tests can be performed. Using aseptic technique, a loop of bacteria is transfered to a tube of MR-VP broth. After 48 hours of incubation, a few milliliters of broth is transfered to a sterile test tube. The initial test tube is marked 'methyl red' and the second test tube is marked 'voges-proskauer'. To the tube marked 'methyl red', one dropper full of methyl red indicator is added. This indicator turns red at pH 4.4 and below. It becomes yellow at pH 6.2 and above. If when added the reagent remains red, the pH has risen. This is because great amounts of acid were produced through dextrose conversion. If the solution is orange or yellow upon addition of methyl red, there is less acid production. It is possible that if the solution is orange or yellow upon addition of methyl red that further incubation is needed. An additional 24 hours of incubation is advised when this occurs. To the test tube labeled 'voges-proskauer', 15 drops of Barritt's reagent A and 15 drops of Barritt's reagent B are added. For 30 minutes, the tube needs to be mixed periodically with the use of an electronic mixer. If the solution turns pink, orange, or red, the voges-proskauer test is positive. If the solution remains the same color, the voges-proskauer test is negative.