Cetrimide Agar Composition, Preparation, Principle and Use

Intended use Recommended for the selective isolation of Pseudomonas aeruginosa from water and clinical specimens.

Composition:

Ingredients	Gms / Litre
Gelatin peptone	20.000
Magnesium chloride	1.400
Potassium sulphate	10.000
Cetrimide	0.300
Agar	15.000

Final pH ( at 25°C) 7.2±0.2

Preparation:

Suspend 46.7 grams in 1000 ml purified/distilled water containing 10 ml glycerol.

Heat, to boiling, to dissolve the medium completely.

Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

Mix well and pour into sterile Petri plates.

Principle And Interpretation

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.

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.

Reference: Hi-Media