Deoxycholate Citrate Agar is a modification of Leifson formula and is recommended for the isolation of Salmonella and Shigella sp. Gram positive bacteria and coliforms are inhibited by the addition of sodium desoxycholate and sodium citrate to the formula. H2S producing microorganisms reduce ferric ammonium citrate to iron sulfide and give colonies with black centers. Fermentation of lactose by coliforms causes the pH to shift to acid with the neutral red dye color changing to red and bile to precipitate. Lactose fermenters form pink colonies with bile precipitated around the colonies. Lactose non-fermenters form colorless colonies.

Directions per Liter:

Suspend 73g in 1L of ddH2O. Heat with frequent agitation and boil for one minute to completely dissolve the medium. AVOID OVERHEATING. Pour plates can be prepared after the medium has been cooled to 45-50°C. Do not autoclave.

Storage and Stability:

Store powdered media at RT. Opened bottles should be capped tightly and kept in a dark, low humidity environment. Prepared media should be kept at 4°C and used within a short period of time.