What is IMViC TEST

By Rahul Shakya 


  IMVic test also known as Biochemical test

  • It is used for differentiate same shape or size bacteria belonging to family Enterobacteriaceae. Eg- E.coli , Enterobacter aerogens  
  • IMViC test is group of four different types test.

  • Each letters in IMViC test stands for individual test

I- indole test-

M- methyl red test

V - voges-proskauer test

C - Citrate test 

1-INDOLE TEST

. Tryptophan media 
. Kovac's reagent {10gm p-Dimethylaminobenzaldehyde,150ml amyl or isoamyl alcohol,50ml conc" HCl}

  • Red/Pink colour appers at the top of tube after addition of 0.5ml kovac's reagent.

Principle:-

  • Bacterial culture react with tryptophan media in the +nce of tryptophanase enzyme gives indole(red colour) along with ammonia and amino acids .

Reaction:-

  • Tryptophan-----**Tryptophanase enzyme--> Indole + amino acids + ammonia 
**In the +nce

  • A positive indole result indicates due to appear red layer at the lop of tube.

Procedure;- 

  • Firstly bacterial suspension with agar media and tryptophan peptone tube incubated 2-3days at 37°c in incubator 
  • Then after incubation kovac's reagent is added
  • .A positive indole result indicates due to appear red layer at the lop of tube.
  • A negative indole result indicates due to lack of colour change at the top of tube.



Eg:-E.coli gives Positive test , E.Aerogens gives negative test.


2:-METHYL RED TEST

It is a test for acid production  

Glucose phasphate media
red colour  appear

Principle:-

  •   Bacterial suspension react with Glucose phasphate media gives acid after fermentation .

Reaction:-

  • Glucose + water ---> organic acid (after fermentation)

Procedure:-

  •  Firstly take bacterial suspension with Glucose phasphate media in a peptone tube
  • Then tube incubated for 2-3days at 37°c in incubator for growth of bacteria.
  • A positive results - acid formation after fermentation gives red colour.


 Eg:-E.coli gives positive test {red colour}, E.aerogens gives negative test (yellow colour).

3:- VOGES-PROSKAUER TEST

Glucose phasphate media
Barritt reagent {baraitt's A- alpha naphthol & barritt's B- KOH}
Red/pink colour appear
Principle:- 
  • It is based on the principle of conversion of glucose into acetyl methyl carbinol.
  • Then react with Barritt's reagent to form Diacetyl{ red/pink colour}

Reaction:-
  • Glucose ----> acetyl methyl carbinol ----** barritt's reagent---> Diacetyl ( red/pink colour)
** In the +nce
  
Procedure:- 
  • First of all carry a  peptone tube with a glucose phasphate media and bacterial suspension are mixed.
  • Then peptone tube  placed in incubator for growth of bacteria for 2-3days at 37°c .
  • After incubation period tube carrying out from incubator , then the Barritt's reagent { 0.6ml of 5%alpha--naphthol  ,  0.2ml of 40% KOH} are added into glucose phasphate medium.

A positive result gives red/pink colour eg:- E.aerogens.
Negative result:- E.coli

4- CITRATE UTILIZATION TEST

Simmon's citrate agar media
Bromothymol blue indicator{reagent}

Principle:-
  • simmon's citrate agar medium containing citric acid {source of Carbon}.
  • Utilisation of citrate is indicated by turbid medium.
Reaction:-

  • Citric acid ---> turbidity
 
Procedure:- 
  • Bacterial suspension and simmon's media tube incubated at  44° c  .
  • Only E.aerogens can grow at this temperature while E.coli will not.


Positive result- E.aerogens
Negative results-E.coli


That's all about IMViC test-.



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