King's Medium B Base

原理

Pseudomonas aeruginosa characteristically secretes several diffusible pigments, including the blue-green pyocyanin, the fluorescent yellow-green pyoverdin (fluorescein), and the reddish-brown pyorubin.¹ King's Medium B Base is formulated to favor the production of fluorescein. Proteose peptone supplies the nitrogen, amino acids, and carbon required for growth, and contributes the phosphorus that stimulates fluorescein synthesis.² The medium contains no added iron; because pyoverdin functions as a siderophore in bacterial iron-uptake systems, its synthesis is markedly up-regulated under iron-limited conditions.² Glycerol serves as the energy source and further enhances pigment formation, while the high phosphate content provided by dipotassium phosphate increases fluorescent-pigment production. Magnesium sulfate supplies essential ions for fluorescein synthesis. This formulation is the basis for distinguishing King's Medium B (favoring fluorescein) from King's Medium A (favoring pyocyanin).¹ After incubation, fluorescein-producing colonies display a characteristic yellow-green fluorescence under ultraviolet light, supporting the presumptive identification of Pseudomonas aeruginosa.³ The medium is also applied in plant bacteriology, where Agrobacterium species are distinguished as non-fluorescent, tumor-inducing organisms on this medium.⁴