This document describes biochemical tests used to identify bacteria, including the Indole test, Methyl Red test, Voges-Proskauer test, and Citrate test. The Indole test detects the production of indole from tryptophan. A positive result is indicated by a yellow or cherry red color change with Kovac's reagent. The Methyl Red test identifies stable acid production from glucose in MR-VP broth, indicated by a red color with methyl red indicator. The Voges-Proskauer test detects acetyl methyl carbinol production from glucose, shown as a pinkish red color change when alpha-naphthol and potassium hydroxide are added.

1. Biochemical TESTs
IMViC

2. INDOLE TEST
01
02 03 04
Test
sample/Test
culture
2% Tryptone
water broth
Incubate 370
C
for 24 hrs
Add 0.5 ml of
Kovac’s
reagent
HCl +
p-dimethylamino
benzaldehyde in amyl
alcohol

3. PRINCIPLE
TRYPTOPHANASE
TRYPTONE → INDOLE + PYRUVATE
KOVAC’S REAGENT
YELLOW
CHERRY RED

4. METHYL RED TEST
01
02 03 04
Inoculate loopful
culture in Glucose
phosphate broth
(MR-VP medium)
Incubate at
370
C @ 24
hours
1ml of the
broth
Add 2-3 drops
of methyl red
indicator

5. PRINCIPLE
GLUCOSE
MIXTURE OF STABLE ACIDS
pH
RED COLOUR

6. Vogues Proskauer TEST
01
02 03 04
Inoculate loopful
culture in
Glucose
phosphate broth
Incubate at
370
C @ 24
hours
3 ml of 0.5%
Alpha
Naphthol
3 ml of 40%
KOH

7. PRINCIPLE
ACETYL METHYL CARBINOL
(ACETOIN)
DIACETYL
PINKISH RED POLYMER
GLUCOSE
𝝰-Naphthol, KOH, O2
Quanidine compounds-Peptones
MRVP broth
CONDENSE

8. CITRATE TEST
01
02
03
Simmon’s citrate
slant
Streak a
loopful of
culture
Incubate at
370
C @ 24
hours

9. PRINCIPLE
Tests bacteria to
utilize citrate as
sole source of
carbon
Citrate permease
Citrate -----> Pyruvate
Ammonium salts
Ammonia
pH
Bromothymol blue
Green → Blue