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Xylose Lysine Deoxycholate (XLD) agar is used for the isolation and detection of Salmonella and Shigella spp. Developed by Taylor, xylose lysine agar base was 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. are able to 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 prior to streaking. For specific procedures refer to appropriate references. -
Yeast extract is obtained from selected autolyzed Saccharomyces cerevisiae cells. This product can be used in preparing microbiological culture media providing readily available soluble vitamins (notably B-complexes), amino acids, peptides, and other essential growth factors. Yeast extract is observed as an animal free source and is therefore used extensively in many non-animal cell culture formulations.
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Yeast extract agar is a nutrient rich medium for the cultivation of non-fastidious bacteria, yeasts and moulds. Recommended for the plate count of microorganisms in water and dairy products. The yeast extract and peptone acts as a source of nitrogen, amino acids, carbon and vitamins. Related Supplements : LS0019 Oxytetracycline Selective Supplement
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This is a selective medium for the isolation and enumeration of yeasts and moulds in dairy products. It is in according to a typical formulation of The International Organisation for Standardisation (ISO). Yeast extract acts as a source of nitrogen, carbon and vitamins in this medium. Glucose is a fermentable carbohydrate. Although the medium has a low pH it is made more selective by the inclusion of chloramphenicol, an antibiotic selective agent.
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In vitro diagnostic. Dehydrated KM0179 Yersinia Selective Agar Base powder can be reconstituted to form a selective plated medium for the isolation and enumeration of Yersinia species from clinical and food samples.
