Deoxycholate Citrate Agar is a modified version of Desoxycholate Agar Leifson’s formula. This medium is ideal for the investigation of pathogenic Enterobacteria in highly contaminated foods and is particularly useful in isolating Salmonella and many Shigella spp. The Gram-positive organisms, coliforms and many Proteus spp. are highly inhibited by the increased concentration of sodium citrate and sodium deoxycholate. Ferric citrate aids in the detection of H2S production. Meat peptone and beef extract provide nitrogen, vitamins, minerals, and amino acids essential for growth. Lactose is the fermentable carbohydrate. Neutral red is a pH indicator and bacteriological agar is the solidifying agent.

It is used in conjunction with Brilliant Green Tetrathionate Bile Broth (Cat. CL-1253) as a confirmation of Salmonella spp. Lactose-fermenting bacteria form red colonies in the presence of Neutral red. Lactose-fermenting colonies may have a deoxycholate precipitation zone around them. Lactose non-fermenters will appear as colorless colonies. H2S producers will have black centers. Salmonella typhi, S. paratyphi and Shigella types yield well-developed colorless colonies while lactose-positive organisms like Escherichia coli are pink to red. A previous enrichment in Selenite Cystine Broth (Cat. CL-1220) or Sodium Selenite Broth (Cat. CL-1222) can also be used.