Pseudomonas Agar For Detection of Pyocyanin

Principle And Interpretation

Pseudomonas Agar is based on the formulation described by King et al (1) and as recommended by U.S. Pharmacopoeia (2) for detecting pyocyanin, a water soluble pigment by Pseudomonas species from clinical specimens such as stools, wounds, and urine. (3). It is also recommended for microbial limit tests for pharmaceutical and other biological preparations by USP. Pseudomonas species are commonly isolated pathogen and is the significant causative agent of nosocomial, skin and burn infections. Pseudomonas strains are reported to produce phenazine pigments like Pyocyanin-blue green redox-active secondary metabolite pigment, pyorubin-rust brown pigment, -oxyphenzine- a breakdown product of Pyocyanin, pyoverdin-a water soluble yellow green pigments also known as fluorescein. Pyocyanin is readily recovered in large quantities in sputum from patients with cystic fibrosis, an infection caused by Pseudomonas (4,5). This medium enhances the formation of Pyocyanin and/or pyorubin and reduces that of fluorescein. Gelatin peptone provides essential nutrients for growth of Pseudomonas, while glycerol provides carbon and energy to the cell. The pyocyanin pigment diffuses from the colonies of Pseudomonas into the agar and shows blue colouration. Potassium sulphate and magnesium chloride enhances the pyocyanin production and suppresses the fluorescein production. Low content of phosphorous in the medium also aids in inhibiting the production of fluorescein. Some Pseudomonas strains produce small amounts of fluorescein resulting in a blue-green colouration. Strains of Pseudomonas aeruginosa that may fail to produce pyocyanin are not detected in this medium. Production of other pigments may mask the presence of pyocyanin.