Cetrimide Agar Base 500g is recommended for the selective isolation and identification of Pseudomonas aeruginosa. This medium promotes the production of fluorescein (pyoverdin) which is a green-yellow fluorescent pigment that oxidizes to yellow. Fluorescein is not soluble in chloroform, unlike pyocyanin (blue-green pigment). The pigment diffuses throughout the medium and the fluorescent yellow green colour is observed. Strains of Pseudomonas aeruginosa are identified from specimens because, in addition to their colonial morphology and the characteristic grape-like odour of aminoacetophenone, they produce pyocyanin, a blue, water-soluble, nonfluorescent, phenazine pigment. P. aeruginosa is the only specie of Pseudomonas or Gram-negative rod known to excrete pyocyanin. Gelatin pancreatic digest provides nitrogen, vitamins, minerals, and amino acids essential for growth. Glycerol is the carbon source. Magnesium chloride and Potassium Sulfate enhance the production of pyocyanin and pyoverdin. Cetrimide is the selective agent as it inhibits the growth of the accompanying microbial flora. The European Pharmacopoeia recommends this medium for "Microbiological examination of non-sterile products: Test for specified microorganisms" for the test of Pseudomonas aeruginosa in products.