Pseudomonas C-N Selective Agar (Cetrimide Agar)

Pseudomonas C-N Selective Agar (Cetrimide Agar) is for the selective isolation of Pseudomonas aeruginosa from a range of samples.

The formula was described by Goto and Enomoto¹ following the demonstration of cetrimide as a selective agent by Lowbury and Collins².

Cetrimide is a quarternary ammonium compound with bactericidal activity against a broad range of Gram-positive organisms and some Gram-negative organisms.

Goto and Enomoto showed that addition of nalidixic acid at 15μg/mL, while at the same time reducing the cetrimide content to 200mg, improved performance. The medium gave better recovery of Pseudomonas aeruginosa with enhanced pigment formation while strongly suppressing Klebsiella, Proteus and Providencia spp., the latter organisms being the troublesome contaminants of conventional cetrimide media.

Pseudomonas aeruginosa produces a number of water soluble iron chelators, including the yellow-green or yellow-brown fluorescent pyoverdin. When pyoverdin combines with the blue water-soluble pyocyanin, also produced by the organism, the bright green color characteristic of Pseudomonas aeruginosa is produced. The addition of magnesium chloride and potassium sulfate in the medium enhances the production of these chelators.

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