Pseudomonas aeruginosa is isolated from a burn wound with mucoid colonies. Which pigment produced by P. aeruginosa gives its characteristic blue-green discolouration, and what is the significance of mucoidy in clinical infections?

• A Pyocyanin (blue-green phenazine pigment) is the characteristic colour; mucoidy (alginate overproduction) in CF lungs protects against phagocytosis and antibiotic penetration, enabling chronic colonisation ✓
• B Pyoverdin (fluorescein) produces yellow-green fluorescence; mucoidy increases antibiotic sensitivity
• C Pyorubin (red pigment) causes the discolouration; mucoidy is seen only in immunocompromised patients and implies worse prognosis solely due to biofilm
• D Pyomelanin (brown-black) is diagnostic; mucoidy indicates transition from acute to chronic non-invasive phenotype

Explanation

P. aeruginosa produces multiple pigments: pyocyanin (blue-green phenazine, inhibits ciliary function and immune cell activity), pyoverdin/fluorescein (yellow-green, siderophore for iron acquisition), pyorubin (red) and pyomelanin (brown-black). Pyocyanin is the dominant characteristic pigment giving purulent wound discharge its blue-green colour. Mucoid strains overproduce alginate (an exopolysaccharide capsule), forming thick biofilms especially in cystic fibrosis (CF) lung infection. Alginate biofilms resist phagocytosis, impede antibiotic penetration, and protect against desiccation — mucoid conversion in CF signals transition to chronic colonisation and worsened prognosis requiring maintenance antibiotic suppression.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.