IMViC are a group of tests naming Indole, Methyl red, Voges Proskauer, & Citrate tests. Microbiologists have developed groups of biochemical tests that they use to differentiate morphologically & physiologically similar organism. One such group is IMViC test. It is used, primarily, to separate coliforms. Coliforms are defined as Gram negative, aerobic or facultative anaerobic, non spore former, rod shaped bacteria that produces acid & gas from lactose within 48 hours at 37 degree celsius.
The coliforms are placed in family Enterobacteriaceae, commonly called enterics. Among the enterics are many species that normally residue in human & in other animal intestines including the common sewage indicator organism E.coli.
Using IMViC test, E.coli is easily differentiated from other morphologically & physiologically similar coliforms like Enterobacter aerogenes. This differentiation is important in testing the water, milk products & sewage effluent where faecal contamination is monitored.
8.1) Indole Production Test
Coliforms are differentiated by their ability to produce the enzyme tryptophanase. This enzyme hydrolyzes the amino acid tryptophan into indole, pyruvic acid & ammonia. Pyruvic acid can be used by the organism in Kreb's cycle or it can enter glycolysis & can be used to synthesize other compounds the cells needs.
The medium employed is SIM(Sulphur, Indole, Motility) medium which includes peptone,& necessary growth factors but is enriched with the amino acid tryptophan. After incubation,as small amount of test reagent i.e Kovac's reagent is added to medium. The reagent contains HCl & dimethylaminobenzaldehyde dissolved in amyl alcohol. Amyl alcohol is insoluble in water thus it forms a separate layer on the top of the medium. In indole positive organisms, dimethylaminobenzaldehyde reacts with indole to produce a roseindole dye which makes the alcohol layer a cherry red color.
The SIM medium can also be used to detect motility of organism & also see whether is produces sulphide or not. Bacteria produce hydrogen sulphide by putrefaction or by anaerobic respiration.In putrefaction sulphur containing amino acid like cysteine is broken down by the enzyme cysteine desulfurase producing pyruvic acid, ammonia & hydrogen sulphide. The ammonia & hydrogen sulphide are excreted from the cell & pyruvic acid is retained for energy production via the Krebs cycle.In the second process, a type of anaerobic respiration, inorganic sulphur(here thiosulphate) becomes the final electron acceptor of the electron transport chain.
Please refer this links as references:
Cited By Kamal Singh Khadka
Assistant Professor in PU, RE-COST, PNC, LA, NA