Cetrimide Agar strides into the microbiology lab like a nightclub bouncer with a VIP list. It only lets the wild, green-glowing star Pseudomonas aeruginosa through the door while escorting most other bacteria straight out.
Here is a tidy, useful specification for you:
Cetrimide Agar – Specification
Purpose
A selective and differential culture medium used for the isolation, identification, and pigment production of Pseudomonas aeruginosa, especially from clinical or environmental samples.
Selective Agent
• Cetrimide (cetyltrimethylammonium bromide)
Inhibits most gram-positive and many gram-negative organisms except P. aeruginosa.
Differential Features
• Stimulates production of pyocyanin (blue-green pigment)
• Enhances fluorescein (yellow-green fluorescence under UV)
Typical Composition (per liter)
| Ingredient | Function | Amount |
|---|---|---|
| Peptone | Nitrogen & growth nutrients | 20 g |
| Magnesium chloride | Enhances pigment production | 1.4 g |
| Potassium sulfate | Enhances pigment production | 10 g |
| Cetrimide | Selective inhibitor | 0.3 g |
| Agar | Solidifying agent | 13.6–15 g |
| Distilled water | — | 1 liter |
| pH | 7.2 ± 0.2 at 25°C | — |
Appearance
• Light yellow to amber solid medium
• No opacities or foreign particles in prepared plates
Incubation Conditions
• Temperature: 35–37°C
• Time: 24–48 hours
Expected Results
| Organism | Growth | Pigmentation |
|---|---|---|
| P. aeruginosa | Luxuriant growth | Blue-green or yellow-green fluorescence |
| Other bacteria | Poor or no growth | No characteristic pigments |
Storage
• Store prepared plates at 2–8°C, protected from light
• Avoid drying or contamination
• Shelf life typically 3–6 months, depending on manufacturer
Quality Control (QC) Strains
| Strain | Result |
|---|---|
| P. aeruginosa ATCC 27853 | Good growth, pigment production |
| E. coli ATCC 25922 | Complete inhibition |
