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Material Safety Data Sheet

Organisms

Organisms this product works with:

Dehydrated Culture Media

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

* This organism is available as a Culti-Loop®

Precautions
Observe the precautions about overheating shown under Directions.
The medium is best used freshly prepared.
Stock cultures of Shigella species may become predominantly in the R-phase when subcultured away from DCA media. Such cultures are difficult to use for control purposes without first heavily streaking the cultures on DCA plates and picking off the few S-phase colonies i.e. the macro-colonies on the agar surface, for further subculture.
When making biochemical tests on colonies picked from the surface of DCA plates, purity subcultures should be carried out because the colony may be contaminated with Escherichia coli present as micro-colonies.

References
1. Leifson E. (1935) J. Path. Bact. 40. 581-599.
2. Fricker C.R. (1987) J. Appl. Bact. 63. 99-116.

 
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