XLD Agar (acc. harm. EP/USP/JP)

Appearance (clearness): clear
Appearance (colour): red
pH-value (25 °C): 7.2 - 7.6
Typical composition (g/litre): Yeast extract 3.0; Sodium chloride 5.0; D(+)-Xylose 3.5; Lactose 7.5; Sucrose 7.5; L(+)-Lysine 5.0; Sodium desoxycholate 2.5; Sodium thiosulfat 6.8; Ammoniumiron(III) citrate 0.8; Phenol red 0.08; Agar-agar 13.5.
Growth promotion test in accordance with the harmonised method of EP, USP and JP.
Inoculum on reference medium (Salmonella typhimurium ATCC 14028 (WDCM 00031)): 10 - 100
Inoculum on reference medium (Salmonella Abony NCTC 6017): 10 - 100
Colony count (Salmonella typhimurium ATCC 14028 (WDCM 00031)):
Colony count (Salmonella Abony NCTC 6017):
Recovery on test medium (Salmonella typhimurium ATCC 14028 (WDCM 00031)): ≥ 50 %
Recovery on test medium (Salmonella Abony NCTC 6017): ≥ 50 %
Colony colour (Salmonella typhimurium ATCC 14028 (WDCM 00031)): red
Colony colour (Salmonella Abony NCTC 6017): red
Black centre (Salmonella typhimurium ATCC 14028 (WDCM 00031)): +
Black centre (Salmonella Abony NCTC 6017): +
Growth (Escherichia coli ATCC 8739 (WDCM 00012)): none to very good
Colony colour (Escherichia coli ATCC 8739 (WDCM 00012)): yellow
Medium colour (Escherichia coli ATCC 8739 (WDCM 00012)): yellow
Precipitate (Escherichia coli ATCC 8739 (WDCM 00012)): +
Incubation: Salmonella 18 hrs.; 30-35°C; E.coli up to 48 hrs
The information above is current at this time of publication and is subject to change without notice (except for customers holding a change control agreement with our company). The information/format can be altered at any time and inany way if internal company matters or Standard Regulationsdo say so.

We offer two media types: the superior granulated GranuCult^® and the cost-efficient powdered NutriSelect^® culture media, depending on your needs.
The designations basic, plus, or prime are added to indicate the quality control level, from basic quality control to standard QC plus to prime for full regulatory compliance.

Typical colonies of Salmonella exhibit a black center surrounded by a translucent red zone due to indicator color changes. H₂S-negative Salmonella, such as Salmonella paratyphi A, grow as pink colonies with a dark pink center. The degradation of xylose results in acidification, causing the medium to turn yellow. Strains with lysine-decarboxylase activity convert L(+)-lysine into cadaverine, causing alkalization and a red-violet coloration of the medium. This activity neutralizes the acids produced during xylose degradation, resulting in a red-violet medium. Lactose and sucrose are added to differentiate lysine-decarboxylase-positive coliform bacteria from Salmonella, as their acid formation cannot be neutralized by cadaverine, leaving the medium yellow. Deoxycholate inhibits coliform bacteria growth, while thiosulfate and iron (III) salt react with hydrogen sulfide to form black iron sulfide precipitates in colonies. Sodium thiosulfate is reduced by Salmonella and other sulfate-reducing bacteria to H₂S, which reduces ferric ammonium citrate to black iron sulfide. This reaction is more pronounced under alkaline conditions, but H₂S-producing bacteria that form acids from lactose or sucrose, such as Citrobacter spp. and Proteus spp., may show weaker black centers. Salmonella typhi colonies often appear yellow-orange or pink.

GRANUCULT is a registered trademark of Merck KGaA, Darmstadt, Germany

NutriSelect is a registered trademark of Merck KGaA, Darmstadt, Germany

XLD Agar has diverse applications across industries. In the food and beverage sector, it is used to detect Salmonella and Shigella in meat, dairy, and processed foods, ensuring compliance with safety standards. In water quality testing, it identifies pathogenic Enterobacteriaceae to ensure the safety of drinking water. The pharmaceutical industry employs XLD Agar for microbial testing to detect contamination in products, adhering to pharmacopeial standards.

XLD Agar (Xylose Lysine Deoxycholate Agar) is a selective and differential medium used for isolating and differentiating pathogenic Enterobacteriaceae, particularly Salmonella and Shigella species. The media consists of yeast extract for vitamins, peptic digest of animal tissue for nitrogenous compounds, and agar as a solidifying agent. Xylose, lactose, and sucrose serve as fermentable carbohydrates. L(+)-lysine detects lysine-decarboxylase activity, causing alkalization and a red-violet color. Sodium thiosulfate and ferric ammonium citrate react with hydrogen sulfide to form black iron sulfide precipitates in colonies. Sodium deoxycholate inhibits coliform bacteria, ensuring selectivity.