This test is performed to differentiate Enterobacteria.

v  Principle:-

Some Enterobacteria when cultured in buffered glucose peptone water, ferment glucose to produce sufficient acidity, which gives a red color with methyl red indicator (pH range: 4.4-6.2. Color change: red to yellow).

v Procedure:-

1.      Inoculate a colony of the test organism into 0.5 ml of sterile glucose phosphate broth.

2.      Incubate overnight at 35-37°C.

3.      Add a drop of methyl red indicator and observe the color.

v Observations:-

1        Bright red color                  :                Positive test

2        Yellow/orange color         :                 Negative test

v Quality control:-

Use following microorganisms to confirm the reliability of reagents:

Positive control      :               E. coli

Negative control    :               Klebsiella aerogenes