For selective isolation and enumeration of Salmonella typhi and other Salmonella species. XLD Agar was formulated by Taylor for the isolation and differentiation of enteric pathogens including Salmonella Typhi from other Salmonella species. XLD Agar has been recommended for the identification of Enterobacteriaceae and for the microbiological testing of foods, water and dairy products. The media formulation does not allow the over growth of other organisms over Salmonella and Shigella. The medium contains Yeast extracts as source of vitamins and minerals. Addition of Sodium deoxycholate acts as a selective agent which is inhibitory to Gram-positive bacteria. It suppresses the growth of other enteric pathogens and enhances the growth of only few enteric bacilli. The medium contains Xylose as a fermentable carbohydrate which is utilized by Salmonella species. The medium pH is changed due to fermentation of Xylose which is detected by indicator Phenol red, thus the colony colour turns red. The medium also contains Lactose and Sucrose as the source of fermentable sugar. L-lysine is an essential amino acid source. Lysine is added to differentiate Salmonella Sp. Sodium chloride helps maintaining the osmotic balance of the cells. This medium also allows differentiation of bacilli based on their ability to produce H2S; it contains Sodium thiosulphate and Ferric ammonium citrate that helps visualizing the black centered colonies on production of hydrogen sulphide in the medium. Agar is added as the solidifying agent.