Xylose Lysine Deoxycholate (XLD) Agar (ISO)

Xylose Lysine Deoxycholate (XLD) Agar (ISO) is a selective agar for the detection of Salmonella spp. in food, animal feed and in environmental samples from the food production area as described in ISO 6579-1:2017. Xylose Lysine Deoxycholate (XLD) Agar (ISO) is not intended for use in the diagnosis of disease or other conditions in humans.

A selective, diagnostic agar for the detection of Salmonella spp. in food, animal feed and in environmental samples from the food production area as described in ISO 6579-1:2017. Originally formulated by Taylor to differentiate enteric pathogens, the agar is widely used as the preferred differential medium for Salmonella spp. The medium is void of peptones but instead uses yeast extract as a carbon, nitrogen and vitamin source and xylose, lactose and sucrose are fermentable carbohydrates. Salmonella are able to ferment xylose to produce acid but not lactose or sucrose. When the xylose is exhausted Salmonella will decarboxylate lysine shifting the pH back to neutral. At near neutral pH, Salmonella can reduce sodium thiosulfate producing hydrogen sulfide which creates a complex with ferric ammonium citrate to produce black or black centred colonies. Other organisms are able decarboxylate lysine but acid production from the fermentation of lactose and sucrose keeps the pH too acidic for H2S production. Selectivity is achieved through the incorporation of sodium deoxycholate and phenol red acts as a pH indicator. According to ISO 6579-1:2017, subculture is performed separately from both Rappaport-Vassiliadis medium with Soya (RVS) and Muller-Kauffmann tetrathionate-novobiocin (MKTTn) broth. This medium conforms to the performance and formulation requirements of ISO 6579-1:2017.