D.C.A.

(Desoxycholate Citrate Agar)

LAB 29

Description

This is Leifson's original formulation of this selective medium for the isolation of Salmonella spp. and Shigella spp. from faeces and environmental samples. It has approximately half the quantity of inhibitors used in the Hynes modification. The medium uses sodium citrate and sodium desoxycholate as inhibitors. Sodium thiosulphate is the substrate for the enzyme thiosulphate reductase being broken down to form sulphite and hydrogen sulphide. The hydrogen sulphide reacts with the ferric ions to produce a black precipitate of ferrous sulphide. This gives a typical black centre to the colonies of most species of Salmonella.

References

Hynes. M. (1942). The isolation of intestinal pathogens by selective media. J. Path. Bact. 54. 193-207.

Liefson. E. (1935). New culture media based on Sodium desoxycholate for the isolation of intestinal pathogens and for the enumeration of colon bacilli in milk and water. J. Path. Bact. 40: 581-589.