CETRIMIDE AGAR (as per USP/EP/JP/BP)

Cetrimide Agar was described by King et al. This media formulation is in accordance with the harmonized method of USP/EP/BP/JP/IP. It is used as a selective medium for the isolation of Pseudomonas aeruginosa from pharmaceutical products.

Cetrimide Agar is also recommended for microbial limit testing of non-sterile products. Lowbury first reported the use of cetrimide as an agent for selective isolation of Pseudomonas spp. This medium is also used for determining the ability of an organism to produce fluorescein and pyocyanin. Cetrimide (N-acetyl-N,N,Ntrimethylammonium bromide) is added to the medium to suppress bacteria other than Pseudomonas aeruginosa. As a cationic detergent, quaternary ammonium compounds like this release nitrogen and phosphorus from cells of bacteria other than pseudomonas aeruginosa. Magnesium chloride and potassium sulphate incorporated in the medium enhances the production of pigment pyocyanin, which is a bluegreen pigment, diffusing into the medium. This improves detection of Pseudomonas spp. on this medium. Presence of magnesium ions can also neutralize the EDTA, if present in the sample. Pancreatic digestion of gelatin provides the essential nutrients for growth of Pseudomonas spp., while glycerol serves as a slow and continuous carbon source for the growing cells. Samples may be inoculated directly, or after enrichment, on a large non- selective medium, e.g. Soybean Casein Digest Medium, depending on the microbial load for isolating the strains effectively.

Cetrimide Agar enhances the distinctive pigment production of Pseudomonas aeruginosa, colonies could become greenish due to pyocyanin and may also show fluorescence under UV light. This visual identification is helpful for rapid presumptive detection. To prevent contamination the samples must be handled properly and under sterile conditions. After use, all materials should be sterilized before disposal. Cetrimide Agar performs reliably when prepared and used as per recommended conditions.

for selective isolation of Pseudomonas aeruginosa