|
Principle
- Deoxycholate citrate agar is a modification of Desoxycholate Agar as formulated by Leifson for the recovery of intestinal pathogens from specimens containing normal intestinal flora. Deoxycholate citrate agar medium is consisting of meat extract, protease peptone, lactose, sodium deoxycholate, sodium thiosulphate, ferric ammonium citrate, sodium citrate, neutral red, and agar.
- Meat infusion from protease peptone is the source of nitrogen, carbon, and other growth factors required for growth. Lactose is a fermentable carbohydrate. Sodium deoxycholate, ferric ammonium citrate, and sodium citrate inhibit the growth of gram-positive bacteria.
- Sodium thiosulphate is the source of sulfide reduced to hydrogen sulfide and reacts with an iron salt yielding iron sulfide. Neutral red is a pH indicator and agar is a solidifying agent. Differentiation of enteric bacilli is based on the fermentation of lactose.
- Bacteria that ferment lactose produce acid and, in the presence of neutral red, form pink-colored colonies. Bacteria that do not ferment lactose form colorless colonies. The majority of normal intestinal bacteria ferment lactose (pink colonies) while Salmonella and Shigella species do not ferment lactose (colorless colonies). The organisms known to reduce ferric ammonium citrate to iron sulfide are indicated by the blackening of the central position of the colony.
|
