DESOXYCHOLATE CITRATE AGAR - DCA (Hynes modification)

 

A medium inhibitory for commensal gut flora whilst allowing growth of Salmonella and Shigella spp.

 

Code: CB1/1027

 

Typical formula g/l

 

Beef extract	5.0o:p>
Balanced peptone	5.0
Lactose	10.0
Sodium thiosulphate	5.4
Sodium citrate	8.5
Ferric citrate	1.0
Sodium desoxycholate	5.0
Neutral red	0.02
Agar	12.0

 

pH: 7.4 ± 0.2

 

Description

 

A modification of Leifson’s D.C.A. medium introduced in 1942. The medium was designed to be more inhibitory to commensal flora whilst allowing for adequate growth of Salmonella spp and Shigella spp. The citrate and desoxycholate levels are significantly increased. To keep the desoxycholate in solution the pH also had to be increased. The medium still uses lactose fermentation and hydrogen sulphide production as differential indicators.  

 

Method for reconstitution

Weigh 52 grams of powder, disperse in 1 litre of deionised water in a two litre flask. Bring to the boil over a gauze, swirling frequently to prevent burning. Simmer for 30 seconds to dissolve. Cool to 47°C before pouring plates. Dry the surface before inoculation. DO NOT REMELT OR AUTOCLAVE THIS MEDIUM.

 

Appearance: Pink, clear, bile aggregates may appear on the surface on refrigeration.

 

Q.C. organisms:  Salmonella sp. NCIMB 50076 & E. coli NCIMB 50034

 

Storage of Prepared Medium: Plates - up to 7 days at 2-8°C in the dark.

Inoculation: Surface, streaking out for single colonies.

Incubation: 37°C aerobically for 24 hours.