Which pigment produced by Pseudomonas aeruginosa is responsible for its characteristic blue-green colour on culture media and has antimicrobial properties?

Explanation

## Pseudomonas aeruginosa Pigments **Key Point:** Pyocyanin is the blue-green phenazine pigment that gives P. aeruginosa its characteristic colour and is a virulence factor. ### Major Pigments of P. aeruginosa | Pigment | Colour | Function | Clinical Significance | |---------|--------|----------|----------------------| | **Pyocyanin** | Blue-green | Redox-active, generates ROS, inhibits host defences | Hallmark of P. aeruginosa; indicates active infection | | **Pyoverdine** | Yellow-green fluorescent | Iron siderophore; iron acquisition | Fluorescence under UV light (365 nm) | | **Pyorubrin** | Red-brown | Minor pigment | Less clinically relevant | | **Lipopolysaccharide** | Colourless | Endotoxin, not a pigment | Part of outer membrane | **High-Yield:** Pyocyanin is the most characteristic and clinically relevant pigment. It is: - A redox-active phenazine compound - Generates reactive oxygen species (ROS) - Inhibits ciliary function and host immune responses - Detected in sputum of cystic fibrosis patients with chronic P. aeruginosa colonization **Clinical Pearl:** The presence of blue-green sputum or wound exudate is pathognomonic for P. aeruginosa infection and does not require culture confirmation for presumptive diagnosis in clinical practice. **Mnemonic:** **PYO-CYAN** = **PYO** (pus-related) + **CYAN** (blue-green colour).