Deoxycholate Citrate Agar

These media composed of;

Agar

Neutral red

Meat extract

Sodium deoxycholate

Lactose

Proteose peptone

Ferric citrate

Sodium citrate

Sodium thiosulphate

Preparation strictly on manufacturer instruction

These media is used as a selective media for examination and identification of shigellae and salmonellae species. Neutral red is used as an indicator, while sodium deoxycholate (bile salt) serve as an inhibiting agent, the substance inhibit the growth of several gram-positive organisms, and permits the growth of intestinal gram-negative however sodium deoxyholate is a poisonous substance in the present of sodium citrate, and sodium thiosulphate is also poisonous to coliorms, also some degree in salmonellae species, but this poisonous substance are render non poisonous by addition of ferric citrate, these substance that that render the media non poisonous only confer to salmonellae species, it does not take effect on coliform micro organism. The reason why coliform micro organism doe not growth on these media effectively is because they do not grow as of that of non lactose fermenters, the growth of coliform yield pinks color of colony because of the acid produce round the colony of the species cause the sodium deoxycholate to separate from the colonies which permit the organism to growth effectively. The case of proteus species it show a colorless and the colony remain in cluster without spreading, and a small black dot appears in the center of the cluster colonies, and poses odour like that of fish. Colorless colonies also show by shigellae and salmonellae species, but in some case of shigellae when left for sometimes it later develop a pink color doe to ingestion of lactose fermentation by the organism. Doe to fermentation of thiosuphate (H₂S) reaction with ferric citrate in the media to form ion sulphate, this reaction result in formation of black dot in the center of salmonellae colonies in the media.