The litmus milk decolorization test is an important biochemical; test used to identify the clostridia.

Litmus milk test principle

A heavy inoculum of the test organism is incubated for up to 4 hours in a tube containing litmus milk. A change indicates a reduction of litmus milk in the medium color from mauve to white or pale yellow.

Litmus milk medium composition

Following are the test components.

  • Litmus Granules – 80 g
  • Ethanol – 300 ml
  • Milk – 500 ml

Distribute in 5 ml aloquete to small screw-capped bottle. Sterilize it by steaming it for 20 minutes on three successive days.

Litmus milk medium preparation steps

  • Solution A – 300 ml (litmus solution)
  • Solution B – 250 ml (skimmed milk)

Following are the steps

Litmus milk test procedure, result, purpose in microbiology
Litmus milk test
  • Grinde the granules in 150 ml ethanol alcohol and transform them into a flask.
  • Boil the flask for 1 minute and decent to another flask.
  • Add the remaining alcohol to the flask and boil for another one minute. Decent this to the other flask.
  • Now add hydrochloric acid (HCl) drop by drop, while shaking the flask continuously until the medium color change to purple.
  • Steam the milk for 20 minutes and let stand overnight for the cream to separate.
  • Siphon the milk into a clean flask.

Litmus milk decolorization test procedure steps

Following are the steps in the L.milk test

  1. Using a large, sterile loop. Inoculate 5 ml of sterile litmus milk medium with the test organism.
    • NOTE: A heavy inoculum must be used.
  2. After inoculation, incubate that medium at 35 to 37 C for up to 4 hours.
  3. Examining at half-hour interval for a reduction reaction by a change in color from mauve to white or pale yellow.

Litmus milk test result

  • If the medium color change to white or pale yellow. The litmus milk test will be positive.(C. perfringens)
  • But if the medium color remains unchanged, the result will be negative (Strept Viridans).

What is the Litmus milk test used for?

The litmus milk decolorization test is an important biochemical; test used to identify the clostridia.

Which bacteria shows litmus milk test positive?

The litmus milk test will be positive in the case of C. perfringens.

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