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BACKGROUND
Milk is a very complicated source of nutrition that consists of protein in an aqueous solution of lactose and minerals. When bacteria are inoculated in this milk, the enzymes secreted by bacteria may bring about changes in the media.1 Litmus is added identify any changes in the pH.
So, the main objective of this test is to differentiate bacteria based on their action on litmus milk.
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REQUIREMENTS
Sample: Test organism
Chemicals: Litmus milk
Miscellaneous: Test tube
Inoculating loop
Incubator
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PROCEDURE
Take litmus milk in a test tube and inoculate it with the test organism. Then incubate it for about 48 hours.2 Then after completion of 48 hours observe the results and again incubate it for another 5 days and observe result.3 Depending on the change in the appearance of the medium, the reaction is estimated.
Observation:4
Pinkish red colour – Acid reaction and lactose fermentation.
Blue colour – alkaline reaction or no fermentation and organisms attacking the nitrogenous substances in the medium.
Clot formation – coagulation of milk protein.
Bubbles in the medium – clot broken up
Purplish blue – no fermentation
White – Reduction of litmus into white leuco-base by enzyme reductase.
Stormy fermentation – acid clot disturbed by lot of gas formation.
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CONCLUSION
Litmus milk is also used for cultivation of lactic acid bacteria.
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REFERENCES
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McFadden, J.F. 2000. Biochemical Tests for Identification of Medical Bacteria. 3rd ed. Lippincott Williams & Wilkins, Philadelphia, PA.
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Davis, J.G. 1935. J. Dairy Res. 6:121.
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Cantarow, A. and B. Schepartz. 1962. Biochemistry. 3rd ed. W.B. Saunders Co., Philadelphia, PA.
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Burrows, W. and J.W. Moulder. 1968. Textbook of Microbiology. 19th ed. W.B. Saunders Co., Philadelphia, PA.
