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DESOXYCHOLATE CITRATE AGAR - DCA (Leifson's medium)

 

For the isola­tion of intestinal pathogens.o:p>

 

Code: CB1/1026

 

Typical formula g/l

 

Peptone 5.00
Beef extract 5.00
Lactose 10.00
Sodium citrate 5.00
Sodium thiosulphate 5.00
Ferric citrate 1.00
Sodium desoxycholate 2.50
Neutral red 0.03
Agar 15.00

 

Final pH 7.3 +/- 0.2

 

Directions

Suspend 48.5g in 1000ml of cold distilled water, heat to boiling, cool to about 45°C and pour into sterile petri dishes.  Dry the agar surface before use. Do not overheat and do not sterilise in the autoclave.

 

 

Description

Desoxycholate Citrate Agar is a modification of Leifson’s medium and is used for the isola­tion of pathogenic enteric bacteria from clinical samples. Desoxycholate Citrate Agar is less selective than Hynes formulation.

 

Technique

Desoxycholate Citrate Agar can be directly heavily inoculated with pathological materials, such as faeces and urine, or it can be used for the subculture from Selenite or other enrichment broths. In the latter case it is better to use a light inoculation of not more than a loopful of broth. Proteus is usually inhibited and, if inoculated on dry plates, does not swarm, but forms large mucoid colonies. E. coli grows poorly, ferments the lactose and forms red colonies. Salmonella and Shigella do not ferment the lactose, and form co­lourless colonies.  The Gram-positive bacteria are completely inhibited. 

 

User quality assurance   (37°C-24 h)

Productivity control

S.enteritidis ATCC 13076: growth, colourless colonies

S.sonnei ATCC 25931: growth, colourless colonies

Selectivity control

E.coli ATCC 25922: poor growth, red colonies

S.aureus ATCC 25923: inhibited

 

Storage

Dehydrated medium: 15-30°C

User prepared plates: 7 days at 2-8°C 

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