Based on the medium described by King, Ward, and Raney, Pseudomonas Isolation Agar is used for the selective isolation ofPseudomonasand differentiation ofPseudomonasaeruginosabased on pigment production. Enzymatic Digest of Gelatine provides nitrogenous sources for bacterial growth. The presence of Irgasan allows the growth ofPseudomonasspp. while suppressing that of Gram-positive and some Gram-negative microorganisms. Magnesium Chloride and Potassium Sulfate enhance the production of the iron chelators pyoverdin (yellow-green or yellow-brown fluorescent) and pyocianin (blue), whose combination produces a characteristic bright green color, byP.aeruginosa. Agar is the gelifying agent.