Ingredients : gms/lit.
Peptone 20.00
Lactose 10.00
Sodium taurocholate 5.00
Sodium Chloride 5.00
Bromo cresol purple 0.01
Final pH (at 25°C) : 7.4+ 0.2
Directions :
Suspend 40.01 grams in 1000 ml distilled water. Heat if necessary, to dissolve the medium and distribute into test tubes with inverted Durham tubes. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
Principle:
Peptone provides nitrogeneous and carbonaceous compounds, long chain amino acids
and other essential growth nutrients. Lactose is the fermentable carbohydrate. Sodium
taurocholate inhibits gram-positive organisms. Sodium chloride maintains the osmotic balance of the medium. Bromocresol purple is the pH indicator in the medium which turns yellow under acidic condition. Lactose fermentation turn the medium yellow due to the acidity produced on lactose fermentation. The colour change of the dye is observed when the pH of the medium falls below 6.8. Lactose non-fermenting organisms like Salmonella and Shigella do not alter the appearance of the medium.