DESOXYCHOLATE CITRATE AGAR

Code: CM0035

A modification of Leifson’s medium for the isolation of intestinal pathogens.

Typical Formula*	gm/litre
Lab-Lemco’ powder	5.0
Peptone	5.0
Lactose	10.0
Sodium citrate	5.0
Sodium thiosulphate	5.0
Ferric citrate	1.0
Sodium desoxycholate	2.5
Neutral red	0.025
Agar	15.0
pH 7.0 ± 0.2

* Adjusted as required to meet performance standards

Directions
Suspend 48.5g in 1 litre of distilled water. With frequent agitation bring to the boil over a gauze and flame to dissolve completely. Mix well and pour plates immediately. Dry the agar surface before use.

THIS MEDIUM IS HEAT SENSITIVE. AVOID EXCESSIVE OR PROLONGED HEATING DURING RECONSTITUTION. DO NOT AUTOCLAVE, OR REMELT.

Description
An Oxoid modification of Leifson medium¹, for the isolation and maximum recovery of intestinal pathogens. It is less selective and inhibiting than Desoxycholate Citrate Agar (Hynes) CM0227 but colonial characteristics are similar on the two media.

Desoxycholate Citrate Agar provides an opaque background against which one may more easily discern the clearing produced by alkali-producing pathogens.

The use of a less selective medium for direct sampling of faeces and a more selective medium for post-enrichment sampling, would be advantageous. Similarly, the less inhibitory medium is often preferable when shigellae are being sought as well as salmonellae².

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared agar plates at 2-8°C.

Appearance
Dehydrated medium: Straw/pink coloured, free-flowing powder
Prepared medium: Pink coloured gel

Quality control

Positive controls:	Expected results
Salmonella typhimurium ATCC® 14028 *	Good growth; straw coloured colonies
Shigella sonnei ATCC® 25931 *	Good growth; straw coloured colonies
Salmonella poona NCTC 4840 *	Good growth; straw coloured colonies
Negative control:
Enterococcus faecalis ATCC® 29212 *	No growth