Gelatin Lactose Medium is used to determine the identity of presumptive Clostridium perfringens. It contains lactose to test lactose fermentation and gelatin to test liquefaction. The lactose fermentation is indicated by the presence of gas bubbles as well as a color change of the medium from red to yellow. The Gelatin is a protein derived by the hydrolysis of collagen, and is found abundantly in bones, skin, tendons, cartilage and animal tissue. It is used in culture media to determine gelatinolysis by bacteria, the gelatinoses produced by the microorganisms hydrolyze the gelatin liquefying a solid medium. Tryptose provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Lactose is the fermentable carbohydrate, producing acid indicated by the phenol red indicator. Phenol red changes to yellow when acid is produced and to red when an alkalinisation of the medium is produced. Cracks or bubbles in the medium indicate gas production.
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