Voges–Proskauer test
The Voges - Proskauer reaction bacterial cultures for the formation of acetoin ( 3-hydroxy -2-butanone, Acetylmethylcarbinol ) examined, which in the alkaline environment with creatine (contained in peptone nutrient medium or as an additive after incubation ) to gain by α -naphthol produces a red color. This test is used to distinguish and identify bacteria, particularly Enterobacteriaceae, and is a component of the so-called IMViC reactions, allowing a part of the so-called multi-colored series or in the form of commercial test systems such as the Analytical Profile Index a substantial differentiation.
The Enterobacteriaceae can be classified in terms of their fermentation products into two groups. This is the one of the Escherichia coli type, which forms mainly various organic acids from glucose - in the mixed acid fermentation - and on the other the Enterobacter - type of glucose in the 2,3 - butanediol Butandiolgärung especially ( and acetoin as intermediate) and gas (CO2 and H2) forms, but only slightly acid. The formation of acids is the methyl - sample ( also called MR test ) detected during the formation of acetoin as a precursor of 2,3- butanediol in the Voges - Proskauer test ( abbreviated as VP- test ) can be detected.
For example, the bacteria of the genera Enterobacter, Klebsiella and Serratia in the 2,3 - Butandiolgärung glucose from 2,3-butanediol and acetoin as an intermediate. For them, that is, the Voges - Proskauer reaction is positive. They are therefore, in contrast to other genera of the Enterobacteriaceae, such as Escherichia, Proteus, Citrobacter, Salmonella, Shigella, and which do not form acetoin, and in which therefore the Voges - Proskauer reaction is negative. It should be noted that this is a rough categorization, individual species of a genus may have deviating results. When identifying to the species level with the aid of miniaturized test systems, for example a percentage table is used as an aid in the evaluation, therefore, in which is given, in what percentage of the tested representatives of a kind of a certain reaction is positive or negative.