Palcam Agar is used for the selective isolation and enumeration of Listeria monocytogenes from foods and environmental samples. Columbia Blood Agar Base is a general-purpose growth medium. Mannitol and Phenol Red have been added to differentiate Mannitol-fermenting strains of possible contaminants. Polymyixin B, Acriflavin, Ceftazidime, and Lithium Chloride are selective agents used to suppress the growth of Gram-negative and certain Gram-positive bacteria. Esculin and Dextrose are the main energy sources for bacterial growth. Members of the Listeria group hydrolyze Esculin to 6,7-dihydroxycoumarine, which reacts with Ferric Ammonium Citrate and results in the blackening of the medium. Agar is the gelifying agent.