名稱：XLD Medium
貨號：oxoid CM0469
規格：500g
產品說明：
X.L.D. AGAR
Code：CM0469
Xylose-Lysine-Desoxycholate Agar was originally formulated by Taylor1 for the isolation and identification of shigellae from stool specimens. It has since been found to be a satisfactory medium for the isolation and presumptive identification of both salmonellae and shigellae2. It relies on xylose fermentation, lysine decarboxylation and production of hydrogen sulphide for the primary differentiation of shigellae and salmonellae from non-pathogenic bacteria.
Rapid xylose fermentation is almost universal amongst enteric bacteria, except for members of the Shigella, Providencia and Edwardsiella genera1. Xylose is thus included in the medium so that Shigella spp. may be identified by a negative reaction.
Salmonella spp. are differentiated from non-pathogenic xylose fermenters by the incorporation of lysine in the medium. Salmonellae exhaust the xylose and decarboxylate the lysine, thus altering the pH to alkaline and mimicking the Shigella reaction. However, the presence of Salmonella and Edwardsiella spp. is differentiated from that of shigellae by a hydrogen sulphide indicator.
The high acid level produced by fermentation of lactose and sucrose, prevents lysine-positive coliforms from reverting the pH to an alkaline value, and non-pathogenic hydrogen sulphide producers do not decarboxylate lysine. The acid level also prevents blackening by these micro-organisms until after the 18-24 hour examination for pathogens.