Listeria Agar Base Palcam, used with supplements, is a selective and differential medium for Listeria spp. It is recommended by ISO 11290 for the detection and enumeration of Listeria monocytogenes in food products and clinical samples, and can also be used for environmental samples. It is used after a primary and secondary enrichment stage, using Listeria Enrichment Broth Base (Cat.1120). It allows the easy differential diagnosis of Listeria monocytogenes using a double-system indicator: Esculin/Iron and Mannitol/Phenol red. All Listeria species hydrolyze the esculin to esculetin, which reacts with iron ions producing a blackening of the medium. Lithium chloride included in the medium, along with ceftazidime, polymyxin B sulfate and Acryflavine from the supplement, inhibit the growth of the non-Listeria accompanying bacteria present in foods, which can hydrolyze the esculin. Peptones and maize starch provide a rich nutrient base for growth. Yeast extract is the source of vitamins, particularly of the B-group. Glucose is the fermentable carbohydrate. Ferric ammonium citrate improves the growth of L. monocytogenes. The Mannitol/Phenol red differentiation system is used to differentiate Listeria spp that do not ferment mannitol from other species that occasionally grow in the medium such as enterococci or staphylococci. Differentiation is achieved by the acid increase in the media, causing the phenol red indicator to change the color of the medium from red to yellow. Confirmation of Listeria is done by biochemical and serological identifications tests.
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