MR-VP test for all of You!!!

Biochemical Tests
a. The IMViC Test - 4 tests (indole, methyl red, Voges-Proskauer, citrate) used to differentiate E. coli from the other two coliforms (Klebsiella and Enterobacter).
Indole Test - E. coli can hydrolyze the amino acid tryptophan to indole, pyruvic acid and ammonia. Spot indole testing may be performed by picking up a colony with a swab and then adding a drop of indole reagent to the swab. A positive test is indicated by the appearance of a red color. It is a rapid test useful in differentiating E. coli from the other coliforms Enterobacter and Klebsiella, which are indole-negative. The indole test is also useful in differentiating species within the same genus, e.g. Proteus vulgaris is indole positive, but P. mirabilis is indole negative.
Indole Tube Test: Klebsiella pneumoniae is indole negative as shown on the left and E. coli is indole positive as shown on the right.
MRVP Test (methyl red and Voges-Proskauer) - E. coli is methyl red positive, fermenting glucose to pyruvic acid, which turns the methyl red pH indicator in the sugar broth red. Enterobacter and Klebsiella initially ferment glucose to pyruvic acid, but later metabolize these acids to CO2 and acetylmethylcarbinol, causing an alkaline shift. Several drops of alpha-naphthol are first added to the MRVP broth culture followed by an equal number of KOH drops. If this results in a red color, the isolate is VP positive. Escherichia coli is MR positive but VP negative. Enterobacter, Klebsiella and Serratia are MR-negative and VP-positive. Pseudomonas (a non-fermenter) is MR-negative and VP-negative.
Citrate Use, i.e., the ability to use citrate as a sole source of carbon and energy characterizes only a few Enterobacteriaceae (Enterobacter, Klebsiella and Citrobacter). Simmons citrate agar, with bromothymol blue (pH indicator), changes from green to blue if citrate is hydrolyzed.
b. The Oxidase Test- demonstrates the presence of cytochrome oxidase, part of an intracellular system that catalyzes the oxidation of cytochrome c by molecular oxygen, the terminal electron acceptor in the electron transport chain. If oxidase is present, it reduces oxidase reagent, forming a colored end product, indophenol. A small amount of bacteria is applied to filter paper or a cotton swab and a drop of oxidase reagent is added. (Don't use a Nichrome inoculating loop to transfer cells; this will cause false positives). If a purple color develops, the isolate is oxidase positive.
The oxidase test is negative for all the Enterobacteriaceae. It is positive for the oxidative non-fermenters, Pseudomonas and Burkholderia, which grow as white colonies on MacConkey Agar. Neisseria, Hemophilus and Moraxella (Branhamella), Vibrio, Campylobacter, and Helicobacter are other oxidase-positive bacteria.