Cetrimide Agar | Principle | Preparation | Results
☰ Content :
Ⅰ. Overview
Cetrimide agar, or pseudomonas agar Cetrimide, is a selective and differential medium used for the isolation and identification of Pseudomonas aeruginosa from water and clinical specimens.
Cetrimide is a quaternary ammonium compound with bactericidal activity against a wide range Gram-positive and certain Gram-negative organisms, including species of pseudomonas other than Pseudomonas aeruginosa .
Cetrimide agar
Ⅱ. Preparation / composition
Suspend the components, dehydrated powder, in water (45.3 g in 1000 ml of purified/distilled water). Add 10 ml of glycerol and boil to dissolve completely. Sterilize in autoclave at 121°C for 15 minutes.
Cool the medium to approximately 50°C and pour into sterile Petri dishes.
Cetrimide agar composition |
|||
|---|---|---|---|
| Ingredients | gram/ liter | ||
| Gelatin Peptone | 20g | ||
| Magnesium chloride | 1.4g | ||
| Potassium Sulphate | 10g | ||
| Cetrimide | 0.3g | ||
| Glycerol | 10ml | ||
| Agar | 13,6g | ||
Ⅲ. Principle
Cetrimide is a quaternary ammonium salt, which acts as a cationic detergent that reduces surface tension at the point of contact and has precipitating, complexing and denaturing effects on bacterial membrane proteins.
Cetrimide inhibits the growth of many microorganisms while allowing Pseudomonas aeruginosa to develop typical colonies.
P.aeruginosa can be identified by its characteristic production of pyocyanin, a blue, water-soluble, non-fluorescent phenazine pigment, coupled with its colonial morphology and characteristic grape-like odor aminoacetophenone.
Magnesium chloride and Dipotassium sulfate enhance the production of pyoverdin and pyocyanin pigments which combine to give characteristic green colonies of Pseudomonas aeruginosa.
The gelatin peptone provides the necessary nutrients for P.aeruginosa. Sodium chloride maintains osmotic balance in the medium.
Ⅳ. Results
Colonies showing fluorescence at 250 nm and blue or blue-green pigmentation are considered presumptive positive.
Cetrimide Agar
