Prof. Dr. Sevgi ERTUĞRUL KARATAY
Biochemical Tests IMViC Tests
Indole, methyl red, Voges-Proskauer, Citrate tests.
They are used for differentiation of bacteria in
coliform group (eg E. coli and Enterobacter ).
Biochemical Tests Indole Test
It is a test that determines whether bacteria convert tryptophan amino acid to indole.
After the microorganisms are inoculated to liquid medium (containing peptone) and incubated at 37 ºC.
After incubation for 1-5 days, 0.5 mL of Ehrlich reagent is added to the medium. Tubes are mixed thoroughly.
The formation of a red-violet ring within one to two minutes indicates the presence of the indole ring. The yellowish ring
indicates that the microorganisms are indole negative.
Biochemical Tests Methyl Red Test
This test is carried out in the presence of indicator substance similar to fermentation tests.
At the end of the experiment, it is obtained whether glucose is used in fermentative way, organic acids are
formed in the medium and pH decreases.
Methyl red gives a yellow color around pH 6, while its
color turns red at pH 4.4.
Biochemical Tests Voges-Proskauer Test
This test shows whether bacteria break down glucose to form acetoin.
It is used to differentiate the species such as
Klebsiella penumoniae
andE. coli.
Different results can be obtained according to the routes used during the reduction of glucose to pyruvate.
It is added from O’Meara reagent on microorganisms incubated in glucose media. The formation of pink color
in 2-5 minutes indicates the presence of acetoin.
Biochemical Tests Citrate Test
It is a test that shows whether microorganisms use citrate as carbon source and ammonium salts as nitrogen source.
Acetoine and lactate are formed in acidic medium, while more acetate and formate are formed at alkaline pH.
If ammonia is formed during the experiment, the pH of the medium rises.
Carbonates and bicarbonates are formed by the use of organic acids and their salts as carbon sources by bacteria.
