Cetrimide Nalidixic (CN) Agar is used for the detection and enumeration of Pseudomonas aeruginosa in bottled water, water intended for human consumption or swimming pool water (membrane filtration method) according to ISO Standard. This media doesn’t required any supplement anymore.
Principle
P. aeruginosa is a Gram-negative bacteria that grows on selective media containing cetrimide and
produces pyocyanin, a blue-green pigment. Due to the presence of cetrimide and nalidixic acid, the
growth of Gram-positive and some Gram-negative microorganism are inhibited. The presence of
magnesium chloride and potassium sulfate in the medium promotes the production of pyocyanin pigment
by P. aeruginosa.
Theoretical Composition
| Gelatin peptone | 16 g |
| Casein hydrolysate | 10 g |
| Potassium sulfate anhydrous (K2SO4) | 10 g |
| Magnesium chloride anhydrous (mgSO4) | 1.4 g |
| Hexadecyltrimethyl ammonium bromide (cetrimide) | 0.2 g |
| Glycerol | 10 ml |
| Agar | 13 g |
| Distilled water | 1,000 ml |
| Final pH at 25 ⁰C = 7.1 ± 0.2 |
Reconstitution Ratio
50.6 g/L (500 g of powder makes 9.8 L of medium)
Storage
Store dehydrated medium at 15-25 ⁰C in carefully sealed bottles in a cool, dry place
References
– ISO 11133:2014
– ISO 11133/A2:2020
– ISO 16266:2006