CETRIMIDE AGAR BASE

Pseudomonas aeruginosa grows well on all normal laboratory media but specific isolation of the organism, from environmental sites or from human, animal or plant sources, is best carried out on a medium, which contains a selective agent and also constituents to enhance pigment production. Most selective media depend upon the intrinsic resistance of the species to various antibacterial agents. Cetrimide inhibits the growth of many microorganisms whilst allowing Pseudomonas aeruginosa to develop typical colonies.
Cetrimide is a quaternary ammonium salt, which acts as a cationic detergent that reduces surface tension in the point of contact and has precipitant, complexing and denaturing effects on bacterial membrane proteins. It exhibits inhibitory actions on a wide variety of microorganisms including Pseudomonas species other than Pseudomonas aeruginosa. King et al developed Medium A for the enhancement of pyocyanin production by Pseudomonas. Cetrimide Agar developed by Lowburry is a modification of Tech Agar (Medium A) with addition of 0.1% cetrimide for selective isolation of P.aeruginosa. Later, due to the availability of the highly purified cetrimide, its concentration in the medium was decreased. The incubation was carried out at 37?C for a period of 18-24 hours.
P.aeruginosa can be identified due to their characteristic production of pyocyanin, a blue, water-soluble, non-fluorescent phenazine pigment coupled with their colonial morphology and the characteristic grape-like odor of aminoacetophenone. P.aeruginosa is the only species of Pseudomonas or gram-negative rod known to excrete pyocyanin. These media are therefore, important in the identification of P.aeruginosa. These media are used for the examination of cosmetics and clinical specimens for the presence of P.aeruginosa, as well as for evaluating the efficacy of disinfectants against this organism.

for selective isolation of Pseudomonas aeruginosa from clinical samples