Xylose Lysine Desoxycholate Agar (XLD)

Xylose Lysine Deoxycholate (XLD) agar is used for the isolation and detection of Salmonella and Shigella spp.

Xylose lysine agar base used for isolating and differentiating Gram-negative enteric bacilli. The addition of sodium thiosulfate, ferric ammonium citrate, and sodium deoxycholate created the more selective medium, XLD agar.

This medium was found to be satisfactory for the isolation of Shigella and Providencia spp, as well as proving to be an effective differential media. The yeast extract is the source of the required nitrogen, carbon and vitamins. Lactose, sucrose and xylose are fermentable carbohydrates.

Sodium deoxycholate, sodium thiosulphate and ferric ammonium citrate are selective agents. Phenol red acts as a pH indicator. Sodium chloride maintains the osmotic balance. Most enteric bacteria including Salmonella spp., can ferment xylose to produce acid. Shigella spp. are unable to do this and thus the colonies remain red.

Once xylose has been completely utilized Salmonella spp. will decarboxylate lysine resulting in a pH increase to alkaline. Salmonella and Shigella spp. are differentiated as Salmonellae spp. can metabolise thiosulphate producing hydrogen sulphide resulting in colonies with black centres.

Stool specimens or rectal swabs may be plated directly onto XLD agar. Selective enrichment broths, such as Selenite Broth or Tetrathionate Broth, may be used before streaking. For specific procedures refer to appropriate references.

isolation and detection of Salmonella and Shigella spp.

Additional Information

Shelf Life (days): 1095 days

Storage Temp (°C): 10-30°C

Dehydrated Medium Appearance: Fine Powder

Prepared Medium Appearance: Firm Gel

Dehydrated Medium Colour: Pale Straw

Prepared Medium Colour: Light rose

Dehydrated PH: 7.4 ± 0.2

Prepared PH: 7.4 ± 0.2

Recommended Incubation: Aerobically at 37°C for 16-24 hours