Hardy Diagnostics' CRITERION™ MYP Agar Base contains meat extract and peptones that supply nitrogen, vitamins and minerals. Mannitol is the carbohydrate source and phenol red is the pH indicator; thus, bacterial colonies capable of fermenting mannitol will appear yellow. Sodium chloride aids cells in maintaining osmotic equilibrium. When supplemented with polymyxin B and egg yolk emulsion, the medium can be used for the isolation and identification of Bacillus species, particularly B. cereus. Polymyxin B helps restrict the growth of gram-negative microorganisms present in the sample, while egg yolk emulsion helps differentiate lecithinase producing colonies. The insoluble products of egg yolk lecithin accumulate around colonies that produce lecithinase to form a zone of white precipitate