Cetrimide Agar is used for the selective isolation and identification of Pseudomonas aeruginosa.
SUMMARY AND EXPLANATION
King et al. developed Medium A (Tech Agar) for the enhancement of pyocyanin production by Pseudomonas. 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.
In 1951, Lowbury described the use of 0.1% cetrimide in a selective medium for P. aeruginosa. Because of the increased purity of the inhibitory agent, the concentration was later reduced, as reported by Lowbury and Collins in 1955. Brown and Lowbury employed incubation at 37°C with examination after 18 and 42 hours of incubation.
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 morphology and the characteristic grapelike odor of aminoacetophenone. 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.
Cetrimide (Pseudosel) Agar is widely recommended for use in the examination of cosmetics, clinical specimens for the presence of P. aeruginosa, as well as for evaluating the efficacy of disinfectants against this organism. It is also used in the microbiological examination of nonsterile pharmaceutical products for Pseudomonas aeruginosa.
Gelatin peptone supplies the nutrients necessary to support growth. The production of pyocyanin is stimulated by the magnesium chloride and potassium sulfate in the medium. Cetrimide is a quaternary ammonium, cationic detergent compound, which is inhibitory to a wide variety of bacterial species including Pseudomonas species other than P. aeruginosa. Agar is a solidifying agent. Cetrimide Agar Base is supplemented with 1% glycerol as a source of carbon.
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