To study fermentation reactions of members of the Enterobacteiaceae
ANDRADE LACTOSE PEPTONE WATER is used for detection of coliforms with andrade’s indicator when the organism metabolizes the lactose; acids produced with the glycolysis lower the pH of the medium and change the indicator form colourless to pink or red. Medium contains Peptone a source of nitrogen and carbon source for the growth of microorganisms. Lactose is the fermentable carbohydrate providing carbon and energy. Sodium chloride is added to maintain the osmotic balance. Andrade indicator is a solution of acid fuchsin which when titrated with sodium hydroxide; changes colour from pink to yellow. The Andrade indicator changes colour from yellow to pink as the pH decreases. Incubate the tubes at 36 ± 1°C with the caps loosened for 18-24 hours or longer, depending on the organisms to be identified. Pink to red color change indicates carbohydrate fermentation. The medium remains pale tan to straw-colored if the carbohydrate is not fermented. Gas production is indicated by displacement of the broth in the Durham tube. A single bubble is sufficient to report as gas production.