IMVIC

The IMViC is a test used in microbiology for the identification of bacteria. It is made up of four tests: Indole, Methyl Red, Voges-Proskauer and Citrate. The result of this test is expressed using positive or negative symbols (+ or -) according to the result of each test, always following the order established by the initials of the method. For example, the IMViC of the bacteria Salmonella and Citrobacter is -+-+. For E.coli it is ++-- and for Klebsiella and Enterobacter it is --++.

Indole (I)

It consists of cultivating the microorganism under study in a broth rich in tryptophan; After 24-48 hours of growth, xylol broth is added to the tube to separate the indole produced, and after stirring, the Kovacs reagent (p-dimethyl amino benzaldehyde) is added. A positive result will show the formation of a ring of red color on the culture broth, which will reveal the presence of Indole due to the use of tryptophan by the microorganism (the tryptophan molecule is broken and one of those products is Indole), a negative result will only show a ring yellow color typical of Kovacs reagent.

Methyl Red (M)

Methyl red is a pH indicator. (Formula: C15H15N3O2). It acts between pH 4.2 and 6.3, varying from red (pH 4.2) to yellow (pH 6.3). Therefore, it allows us to determine the formation of organic acids that are produced during the fermentation of a carbohydrate. The microorganism under study is grown in a culture broth with some fermentable carbohydrate, the most common being glucose, although other carbohydrates such as lactose, sucrose, mannitol, etc. can be used, added with methyl red as a pH indicator. A positive reaction, that is, the change of the medium to a red color, indicates that the microorganism is fermenting glucose through the mixed-acid route and the pH of the medium becomes up to 4.2 due to the large amount of organic acids produced. A negative test does not change the color of the medium (yellow color)

Voges-Proskauer (Vi)

Some microorganisms produce acetoin or acetyl methyl carbinol by decarboxylation of two molecules of pyruvic acid (final product of glycolysis). Acetoin is an intermediate product of butylene-glycolic fermentation, which leads to the formation of 2, 3 butanediols. Both acetoin and 2,3-butanediol are neutral products of glucose fermentation that bring the pH of the medium to an approximate value of six or more and an increase in the production of carbon dioxide, compared to the Red test. Methyl. Acetoin in a strongly alkaline medium (NaOH or KOH) and in the presence of oxygen is oxidized to diacetyl. Diacetyl reacts with compounds containing guanidine nuclei, such as arginine, present in the medium (peptone, for example) and gives a red-pink-violet compound. α-Naphthol is added to increase sensitivity. This test characterizes certain species of the Enterobacteriaceae, and will indicate that glucose is fermented by the butanediolic pathway.

Citrate (C)

It is used to determine if a microorganism can grow using citrate as the only carbon source due to the synthesis of the enzyme citrate permease which allows the introduction of citrate into the cell, once inside, the citrate is incorporated into the cycle. of tricarboxylic acids or Krebs cycle. The microorganism under study is grown in citrate broth. A positive result is when turbidity is observed in the tube, due to bacterial growth. A negative result is when no growth is observed. Currently the most used medium is Simmons Citrate Agar, a solid medium in a tube with a flute spout which has a pH indicator (bromothymol blue). If the microorganism is able to grow with citrate as the only carbon source, it will also be able to use ammonium salts as the only nitrogen source; With the release of ammonia using ammonium salts, the pH will increase and the indicator will turn blue, giving a positive result. The uninoculated medium is green, in this way with a negative result there will be no growth and the color will remain green.