Litmus milk test procedure, result, purpose in microbiology

The litmus milk decolorization test is an important biochemical; test used to identify 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 eloquent to a 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

• 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 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 intervals 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).