B.T.B. Lactose Agar, Modified (Lactose Blue Agar), 2.5 kg

Reactions with lactose are of great practical importance for the primary isolation of Enterobacteria from clinical specimens. The specimens e.g. faeces is usually plated on a lactose-containing medium on which lactose fermenters and lactose non fermenters form colored and pale colonies respectively due to the dye incorporated. This procedure makes an immediate presumptive distinction between colonies of the true intestinal pathogens possible. Salmonella and Shigella , do not ferment lactose while the common intestinal commensals, Escherichia and Klebsiella , which do ferment lactose (1). Lactose Blue Agar is used for differentiating lactose fermenting and non-fermenting bacteria belonging to the family Enterobacteriaceae . Casein enzymic hydrolysate and peptic digest of animal tissue provide essential nutrients for bacterial metabolism. Lactose provides a fermentable carbohydrate source for the enteric bacteria. Bromo thymol blue is the pH indicator for indicating acid production due to carbohydrate fermentation. The dye turns yellow at acidic pH and imparts yellow colour to the colony. Alkalinization produces a blue coloration. Winkle (2) recommended addition of 0.28g/l metachrome yellow to suppress the swarming of Proteus species. Storage and Shelf-life: Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label. Reference: 1. Cruikshank R., Duguid J. P., Marmion B. P., Swain R. H. A., (Eds.), 1975, Medical Microbiology, The Practice of Medical Microbiology, 12th Edition, Vol. II, Churchill Livingstone 2. Winkle S., 1947, Zbl. Bakt. I. Orig., 152:103.