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Bacillus Cereus Selective Agar Base (MYP) is a medium recommended by the ISO normative 7932 for the presumptive enumeration of Bacillus cereus with the count plate technique at 30 ºC.
Beef extract and enzymatic digest of casein provide nitrogen, vitamins, minerals and amino acids essential for growth. Mannitol is the fermentable carbohydrate providing carbon and energy, Bacillus cereus is mannitol-negative. The mannitol content allows the identification of the accompanying mannitol positive flora, which are characterized by a yellow color. Phenol red is the pH indicator. Bacteriological agar is the solidifying agent. Bacillus cereus is resistant to certain concentrations of polymyxin, which inhibits the accompanying flora, and it is effective mainly against gram-negative organisms. Bacillus cereus produces lecithinases. The insoluble degradation products of the lecithin from egg yolk, are accumulated around the Bacillus cereus colonies, forming a white precipitate. The presumptive colonies are large, pink (indicating that mannitol fermentation has not occurred) and generally surrounded by a zone of precipitation (indicating the production of lecithinase).