24-48 hourstryptic soy broth cultures of organisms
Litmus milk broth (pH-6.8)
Skim milk powder 100g
Distilled water 1,000.0ml
Autoclave at 12lb pressure for 15 minutes
Test tube rack
Using sterile technique, inoculate each experimental organism into its appropriately labeled tube by means of a loop inoculation. The last tube will serve as a control.
Incubate all cultures for 24 to 48 hours at 37˚C.
Figure - Litmus milk reactions: (A) Alkaline. (B) Acid. (C) Upper transparent portion is peptonization; solid white portion in bottom is coagulation and litmus reduction; overall redness is interpreted as acid. (D) Coagulation and litmus reduction in lower half; some peptonization (transparency) and acid in top portion. (E) Litmus indicator is masked by production of soluble pigment.
Litmus milk is a complex medium that can produce a diversity of results. Because of this, litmus milk can give quite unreliable results (i.e., the results often give negative results when something positive should happen). Thus, you would be advised to use litmus milk as a confirmatory test but not a definitive test (except as a last resort).
A clot formation is simply recorded as “clot” and cannot clearly differentiate between a clot and curd formation in this medium.
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