Pigment production in Pseudomonas: which blue, water-soluble pigment is characteristically produced by Pseudomonas aeruginosa in culture?

Introduction / Context:
Pseudomonas aeruginosa is known for producing distinctive pigments that aid identification in the laboratory and are linked to virulence and iron acquisition. Being able to name these pigments is a common exam task in medical microbiology.

Given Data / Assumptions:

• Pyocyanin: blue phenazine pigment; water-soluble; can generate reactive oxygen species and contribute to tissue damage.
• Pyoverdin (fluorescein): yellow-green, fluorescent siderophore involved in iron uptake.
• β-carotene: orange carotenoid, not typical for P. aeruginosa.
• Chlororaphin: not the standard name associated with this species.

Concept / Approach:
Among the pigments of P. aeruginosa, the blue, water-soluble one is pyocyanin. Colonies often appear blue-green due to a combination of pyocyanin (blue) and pyoverdin (yellow-green), especially on certain media.

Step-by-Step Solution:

Verification / Alternative check:
On cetrimide agar or standard media, P. aeruginosa often exhibits a blue-green hue with a grape-like odor; fluorescence under UV indicates pyoverdin, while blue coloration indicates pyocyanin.

Why Other Options Are Wrong:
Chlororaphin: Not the canonical pigment for P. aeruginosa. Pyoverdin: Yellow-green fluorescent; not blue. β-carotene: Orange carotenoid, unrelated.

Common Pitfalls:
Confusing pyocyanin (blue) with pyoverdin (yellow-green). Remember “cyanin” suggests blue.

Final Answer:
pyocyanin