Pseudosel Agar (Cetrimide Agar) is used for the selective isolation and presumptive identification of Pseudomonas aeruginosa from clinical and nonclinical specimens.

King et al. developed Medium A (Tech Agar) for the enhancement of pyocyanin production by Pseudomonas.⁴ Cetrimide (Pseudosel) Agar has the formula for Tech Agar but is modified by the addition of cetrimide (cetyl trimethyl ammonium bromide) for the selective inhibition of organisms other than P. aeruginosa.⁵

In 1951, Lowbury described the use of 0.1% cetrimide in a selective medium for P. aeruginosa.⁵ Because of the increased purity of the inhibitory agent, the concentration was later reduced, as reported by Lowbury and Collins in 1955.⁶ Brown and Lowbury employed incubation at 37°C with examination after 18 and 42 hours of incubation.⁷

Strains of P. aeruginosa are identified from specimens by their production of pyocyanin, a blue, water-soluble, nonfluorescent, phenazine pigment in addition to their colonial morphology⁸ and the characteristic grapelike odor of aminoacetophenone.⁹ P. aeruginosa is the only species of Pseudomonas or gram-negative rod known to excrete pyocyanin. Cetrimide (Pseudosel) Agar, therefore, is a valuable culture medium in the identification of this organism.

In addition to the promotion of pyocyanin production, Pseudosel Agar also enables the detection of fluorescent products produced by P. aeruginosa.

Cetrimide (Pseudosel) Agar is widely recommended for use in the examination of cosmetics,¹⁰ clinical specimens^8,11 for the presence of P. aeruginosa, as well as for evaluating the efficacy of disinfectants against this organism.¹² It is also used in the microbiological examination of nonsterile pharmaceutical products for Pseudomonas aeruginosa.¹