Deoxycholate Citrate Agar (Agar Medium J), 500 g

Deoxycholate Citrate Agar Medium is prepared as per the modified formula of Leifson (1) and is also recommended as per British Pharmacopoeia and is also designated as Agar medium J (2). This medium is used for the isolation and maximum recovery of intestinal pathogens belonging to Salmonella and Shigella groups from foods and pharmaceutical products (3). However, it is recommended to use less inhibitory medium when Shigellae have to be isolated (4). Salmonella major causative agent of enteric disease especially food borne toxic infection and typhoid was first observed by Eberth in 1880. This medium is routinely used to check the presence of Salmonella contamination in food and pharmaceutical products as per BP. Sodium deoxycholate at pH 7.3 to 7.5 is inhibitory for gram-positive bacteria. Proteus and other Gram positive organisms are also inhibited due to higher concentration of both citrate and deoxycholate salts in this medium. The reduction of ferric citrate to iron sulphide by H2S gives the indicative appearance of colonies with black center. Citrate salt, in the concentration included in the formulation, are inhibitory to gram-positive bacteria and most other normal intestinal organisms. Combination of beef extract and meat peptone supplies nitrogen, mineral, vitamin factors required for enhanced growth. Lactose monohydrate supplies fermentable carbohydrate source in this medium. Neutral red acts as indicators, in presence of which lactose fermenters like coliform bacteria give pink colonies while lactose non-fermenters give colorless colonies. Salmonella gives well-developed colorless colonies. Precipitation of deoxycholate by acid produced by lactose fermenters may give a zone of precipitation around the colony. This medium provides essential growth factors for growth of several auxotrophic strains of Paratyphi and Typhi. The selectivity of this medium permits the use of fairly heavy inocula without danger of overgrowth of Shigella and Salmonella by other microflora. Storage and Shelf-life: Store below 30°C in a tightly closed container and prepared medium at 2-8°C. Use before expiry period on the label. References: 1.Leifson, 1935, J. Path. Bact., 40:581.>br /> 2.British Pharmacopoeia, 2009, The Stationery office British Pharmacopoeia. 3.Speck M. (Eds.), 1984, Compendium of Methods for the Microbiological Examination of Foods, 2nd ed., APHA, Washington, D.C. 4.Frieker C.R., 1987, J. Appl. Bact., 63:99.