Modified Litmus Medium w/ reducing agent

Principle And Interpretation

Milk is a complex nutritional source that contains proteins (mainly casein) in an aqueous solution of lactose and minerals. Bacterial enzymes alter the media and may bring about various changes. Litmus is added to the medium to detect pH changes that may occur as a result of these enzymatic reactions. Above pH 8.3, litmus is blue, while below pH 4.5 litmus is red. Fermentation of lactose results in the production of acid, which causes milk to curdle or form a clot at the bottom of the tube. Litmus may also act as an electron acceptor thus becoming reduced by bacterial metabolism. This reaction is observed as a white color in the medium. Milk medium with reducing agent is used for determination of litmus reaction of Clostridium species.

Peptic digest of animal tissue and skim milk provide nitrogen, sulphur, vitamins and other growth nutrients. Sodium thioglycollate is a reducing agent, which absorbs oxygen and creates a reduced environment required by anaerobes. This medium has been found satisfactory for the cultivation of Clostridium species and allows observation of their reactions in litmus milk. In anaerobically grown Litmus Milk cultures, enzymes of Clostridium perfringens attack the proteins and carbohydrates of the milk producing a stormy fermentation with clotting and gas formation (1).