Bromothymol Lactose Blue Agar

Bromothymol Lactose Blue Agaris selective medium used for the isolation of Gram-negative bacteria from urine & faeces.It is used for differentiating lactose fermenting and non-fermenting bacteria belonging to the family Enterobacteriaceae. 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. Sodium Lauryl sulphate inhibits gram positive organisms. Sodium chloride maintains osmotic balance.Escherichia coli appears as yellow coloured colony and Salmonella Typhi as blue/colourless colony.