Cetrimide Selective Agar Slant
A bench reference illustrating growth and fluorescent pigment production of Pseudomonas aeruginosa on selective cetrimide agar.
Bench card visual
Cetrimide agar slants A-B
Read first
Cetrimide is highly selective for Pseudomonas aeruginosa, which exhibits yellow-green to blue-green pigment growth.
A
PositivePseudomonas aeruginosaVigorous growth with glowing blue-green (pyocyanin) and yellow-green (pyoverdine) pigments.
B
NegativeEscherichia coliComplete inhibition of growth; agar slant remains its original clear cream-yellow color.
PositivePseudomonas aeruginosa
Vigorous growth with glowing blue-green (pyocyanin) and yellow-green (pyoverdine) pigments.
NegativeEscherichia coli
Complete inhibition of growth; agar slant remains its original clear cream-yellow color.
What to look for
| Visual clue | Meaning | Student shorthand |
|---|---|---|
| Visible Growth | Resistant to the toxic detergent cetrimide | Shorthand: Positive (+) |
| Yellow-Green Pigment | Fluorescein (pyoverdine) and pyocyanin pigments diffuse into the medium | Exhibits bright green color |
| Complete Inhibition | Growth is fully blocked by cetrimide | Shorthand: Negative (-) |
Cetrimide study readout
| Pattern | What to call it | How to think about it |
|---|---|---|
| Positive | Growth with green-blue water-soluble pigmentation | Presumptive Pseudomonas aeruginosa. |
| Negative | No growth or growth without pigment | Does not support P. aeruginosa identification; correlate with oxidase and glucose oxidation. |
| Method note | Also useful for isolating pure cultures | Maintains selective inhibition of typical skin and respiratory flora in sputum workups. |
Key takeaways
- Specifically isolates and presumptively identifies Pseudomonas aeruginosa.
- Selects via cetrimide (cetyltrimethylammonium bromide) which disrupts membranes.
- P. aeruginosa is a major nonfermenting Gram-negative opportunistic pathogen.
Remember
P. aeruginosa is oxidase (+), cetrimide (+), Grows at 42°C (+), and is ADH (+).