Deoxycholate Citrate Agar

 

Specifications

Ingredients : gms/lit.
Heart infusion solids 10.00
Proteose peptone 10.00
Lactose 10.00
Sodium citrate 20.00
Ferric ammonium citrate 2.00
Sodium deoxycholate 5.00
Neutral red 0.02
Agar 13.50
Final pH (at 25°C) : 7.5 + 0.2

Instrution for use :
Suspend 70.52 grams in 1000 ml of distilled water. Heat to boiling to dissolve the medium completely. DO
NOT AUTOCLAVE. Avoid excessive heating as it is detrimental to the medium. Cool to 45-50°C. Mix well
and pour into sterile petri plates.

Principle :
Heart infusion solids is a source of carbon and nitrogen. Deoxycholate Citrate Agar contains Proteose
Peptone as a source of carbon, nitrogen, vitamins and minerals. Lactose is a carbohydrate. Sodium citrate
and Sodium deoxycholate inhibit gram positive bacteria, coliforms and Proteus species. Ferric Ammonium
Citrate aids in the detection of H2S producing bacteria. Neutral Red is a pH indicator. Agar is a solidifying
agent.
In the presence of neutral red, bacteria that ferment lactose produce acid and form red colonies. Bacteria
that do not ferment lactose form colorless colonies. If the bacteria produce H2S, the colonies will have
black centers. The majority of normal intestinal bacteria ferment lactose and do not produce H2S (pink-red
colonies without black centers). Salmonella and Shigella sp. Do not ferment lactose but Salmonella may
produce H2S (colourless colonies with or without black centers). Lactose – fermenting colonies may have a
zone of precipitation around them caused by the precipitation of deoxycholate in the presence of acid.