selective isolation and enumeration of Bacillus cereus. Bacillus cereus Selective Agar Base is used for selective isolation and enumeration of Bacillus cereus. It is also recommended by the ISO committee for the enumeration of Bacillus cereus. Bacillus cereus is ubiquitously present in soil, food stuff, water and dust. B.cereus is the most commonly encountered and important species in clinical laboratories, from majority of other Bacillus species as under favorable conditions, the organism multiplies and cause gastrointestinal illness. This medium differentiates B.cereus from other bacteria based on basis of lecithinase activity, mannitol fermentation and resistance to polymyxin. Lecithinase activity is the key reaction in differential identification of B.cereus. If unknown isolates produces lecithinase, Bacillus cereus can be presumptively identified by also colonial morphology, hemolytic reactivity reactivity and motility tests. This medium contains enzymatic digest of casein and beef extract, which provide nitrogen source. Mannitol fermentation can be detected by phenol red, which yields yellow colour to the mannitol fermenting colonies due to acid production. Added egg yolk emulsion helps in differentiation of lecithinase producing colonies, which are surrounded by a zone of white precipitate. Addition of Polymyxin B Sulphate helps to restrict growth of gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa. These differentiating media allow differentiation of B.cereus from other Bacillus species by its inability to ferment mannitol and poor sporulation. B.cereus dissimilates egg yolk and gives rise to typical bacilli form colonies with reddish zones and white halos. Acid produced by organisms other than B.cereus often diffuse through the medium, making it difficult to distinguish between mannitol fermenters and non-fermenters. So, it is advised to transfer the suspected colonies to a fresh medium to visualize the true reaction.