Desoxycholate Lactose Agar 1025 Condalab

Desoxycholate Lactose Agar is a differential and slightly selective medium for the isolation of gram-negative enteric bacilli. This medium can be used to isolate and enumerate coliforms from water, wastewater, milk, and dairy products. The desoxycholate and citrate salts inhibit the development of gram-positive organisms. The Bacteriological peptone provides nitrogen, vitamins, minerals, and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Neutral red is a pH indicator and bacteriological agar is the solidifying agent.

In general, it is used for the enumeration of coliforms by the dilution method. This can be achieved by adding 1ml of the desired dilution to an empty Petri dish and pouring it on the cooled (45-50 °C) medium. If the product to be tested is not diluted (e.g. pasteurized milk), it can be added directly to the melted medium and poured plates. It is convenient to put a second layer of medium on the plate after initial solidification. Coliform colonies are lenticular, pink, or bright red. Differentiation is made based on the lactose fermentation: lactose fermenters in the presence of neutral red give red colonies while non-fermenters give colourless colonies (Salmonella and Shigella). If no second layer is applied, the colonies of Escherichia coli which develop on the surface of the plate are large and pink while Enterobacter aerogenes are pale with a pink centre.