12/31/2023 0 Comments Xld plate![]() Lactose acts as a source of carbohydrates. Bile salts and crystal violet act as selective agents that inhibit the growth of Gram-positive organisms, and aid in the selective growth of non-fastidious gram-negative bacteria. MacConkey agar contains four key ingredients (lactose, bile salts, crystal violet, and neutral red) that make it a selective and differential media. Agar is incorporated as the solidifying agent Principle of MacConkey Agar Sodium chloride provides osmotic balance and supplies essential electrolytes for transport. Other ingredients such as enzymatic digest of gelatin, casein, and animal tissue provide nitrogen, vitamins, minerals, and amino acids essential for growth. Lactose present in the medium is fermented by bacteria to form lactic acid that decreases the pH of the agar, and turns the indicator (neutral red) pink, thus differentiating lactose fermenters from non-lactose fermenters. Since Gram-negative enteric bacteria possess a bile-resistant outer membrane, they remain unaffected by bile salts. Key components of the MacConkey medium include crystal violet dye, bile salts, lactose, and neutral red (pH indicator).Ĭrystal violet dye and bile salts prevent the growth of Gram-positive bacteria and fastidious Gram-negative bacteria (such as Neisseria and Pasteurella) making it favorable for the growth of gram-negative bacteria. Modifications of MacConkey Agar Composition of MacConkey Agar Ingredient MacConkey Agar (g/L) Peptone 17 g Polypeptone 3 g Lactose 10 g Bile salts 1.5 g Sodium chloride 5 g Agar 13.5 g Neutral red 0.03 g Crystal violet 0.001 g Distilled water 1 L Final pH 7.1.Remel™ and Oxoid products are now part of the Thermo Scientific brand, combining powerful manual, semi-automated and fully automated test products and a comprehensive line of media and diagnostic products to offer a complete, end-to-end solution to quickly deliver the products you need and the quality results your laboratory depends on. Not all products are available for sale in all territories. This results in blue colonies which are easy to distinguish from the purple Salmonella colonies. Some other Enterobacteriaceae species also produce caprylate esterase, but these are either inhibited or differentiated from Salmonella by the ß-glucosidase substrate. The action of caprylate esterase, present in all salmonellae, results in a purple colony. The action of the enzymes on the chromogens result in a build-up of color within the colony, with the color produced depends on which enzymes the organism possesses. The Inhibigen contained in this medium specifically targets Escherichia coli, with additional compounds added to suppress the growth of other non-target organisms.ĭifferentiation of Salmonella from other organisms is achieved through the inclusion of two chromogens that target specific enzymes: caprylate esterase and ß-glucosidase. XLD Agar is recommended in the ISO 6579 testing of Salmonella and is tested according to ISO 11133-2.īrilliance Salmonella Agar provides a highly selective and easy-to-read medium for the presumptive identification of Salmonella from food and environmental samples. The recovery of salmonellae and shigellae is not obscured by profuse growth of other species therefore, XLD Agar is ideal for the screening of samples containing mixed flora and suspected of harbouring enteric pathogens, e.g., medical specimens or food products. The sensitivity and selectivity of XLD Agar exceeds that of traditional plating media, e.g., Eosin Methylene Blue and Bismuth Sulphite agars, which tend to suppress the growth of shigellae. XLD Agar is a selective media for the isolation and differentiation of Salmonella, relying on xylose fermentation, lysine decarboxylation and production of hydrogen sulfide for the primary differentiation of Shigella and Salmonella spp. Read more results from a single patient sample and produce more diagnostic details of pathogenic organisms while reducing storage capacity issues in the incubator with a bi-plate that includes two widely used microbiological media. Work efficiently and according to the ISO method for Salmonella detection with a bi-plate that combines both Thermo Scientific™ XLD Agar and Brilliance™ Salmonella.
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