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Perform selective and differential isolation of enteric gram-negative bacilli using Salmonella Shigella/XLD Biplate.
Perform selective and differential isolation of enteric gram-negative bacilli, especially Salmonella and Shigella, from clinical specimens using Thermo Scientific™ Remel™ Salmonella Shigella(SS)/XLD Biplate. This biplate is used for isolating bacteria such as Salmonella and Shigella spp1-3. Leifson modified the Desoxycholate-Citrate Agar used for the detection of enteric pathogens4 and added bile salts mixture to inhibit the growth of gram-positive organisms. XLD medium was developed by Taylor5.
Salmonella and Shigella are major causes of bacterial enteric illness with transmission occurring via the fecal-oral route, person-to-person contact, or by the ingestion of contaminated food or water.
The SS agar contains bile salts, brilliant green and citrates which acts as selective agents and inhibit gram-positive bacteria and coliforms. Sodium thiosulfate, a sulfur source and ferric ammonium citrate work as an indicator to enable organisms which produce H2S to form black-centered colonies, including some strains of Salmonella. Lactose is a differentiator.
The XLD agar contains desoxycholate which acts as a selective agent and inhibits gram-positive organisms. Xylose is fermented by most gram-negative bacilli. Lysine acts as a differentiator for Salmonella spp. from non-pathogenic enteric bacilli. Salmonella produces lysine decarboxylase which causes pH to revert to alkaline after xylose is fermented, producing red colonies. Lactose and sucrose are added in excess to prevent lysine-positive coliforms from reverting to alkaline conditions. Sodium thiosulfate, a sulfur source, and ferric ammonium citrate work as indicators to enable organisms which produce H2S to form black-centered colonies under alkaline conditions.
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