Deoxycholate Citrate Agar (DCA)- Composition, Principle, Preparation, Results, Uses


Deoxycholate Citrate Agar (DCA) is a selective and differential medium for the isolation and differentiation of Gram-negative enteric bacilli from clinical and environmental samples. It was first developed by Leifson in 1935 as a modification of the original formulation by Hektoen and Edwards. DCA is especially useful for the detection of Salmonella and Shigella species, which are the major causes of bacterial gastroenteritis and dysentery. DCA inhibits the growth of most Gram-positive bacteria and some Gram-negative bacteria, such as Proteus, Pseudomonas and Providencia, by the presence of sodium deoxycholate and sodium citrate in the medium. DCA also allows the differentiation of lactose-fermenting and non-lactose-fermenting bacteria by the incorporation of lactose and neutral red in the medium. Lactose-fermenting bacteria produce acid from lactose, which lowers the pH of the medium and turns it red. Non-lactose-fermenting bacteria do not produce acid and remain colorless or light pink. In addition, DCA contains ferric ammonium citrate, which serves as an indicator for hydrogen sulfide (H2S) production by some bacteria. H2S reacts with ferric ions to form black iron sulfide precipitate, which can be seen as black centers or dots on the colonies. DCA is a simple and inexpensive medium that can be used for the preliminary screening of enteric pathogens in routine microbiology laboratories. However, it has some limitations that require further confirmation and identification of the isolated organisms by other methods.