What is the characteristic color of Pseudomonas aeruginosa?

Characteristic Color of Pseudomonas aeruginosa

Pseudomonas aeruginosa produces a distinctive blue-green pigment called pyocyanin, which gives the bacterium its characteristic color. 1

Identification of Pseudomonas aeruginosa

Pseudomonas aeruginosa is easily identified in laboratory settings by its characteristic colony morphology and pigment production:

• P. aeruginosa grows well on standard laboratory media such as 5% sheep blood agar or chocolate agar 1
• Selective media like cetrimide agar can facilitate isolation from other bacterial species
• The bacterium produces a blue-green diffusible pigment (pyocyanin) that is a key identifying feature 2, 3
• Plates are typically incubated at 35°C in a 5% CO2 atmosphere for 24 hours 1

Pyocyanin: The Blue-Green Pigment

Pyocyanin is a redox-active phenazine pigment that gives P. aeruginosa its distinctive appearance:

• Synthesized by 90-95% of P. aeruginosa isolates 3
• Appears as a blue-green color in culture media and clinical specimens 2
• Functions as a secondary metabolite with various biological activities 2
• Can be present at concentrations up to 10^-4 M in sputum from patients with cystic fibrosis and bronchiectasis 4

Clinical Significance of Pyocyanin

The blue-green pigment is not just a visual identifier but also has important clinical implications:

• Acts as a major virulence factor for P. aeruginosa 5
• Has antimicrobial properties against other bacteria, potentially helping P. aeruginosa establish dominance in polymicrobial infections 2
• Slows human ciliary beat frequency and can lead to disruption of respiratory epithelium 4
• Demonstrates antioxidant and cytotoxic activity against cancer cell lines 2
• Multidrug-resistant strains may produce less pyocyanin than non-MDR strains, potentially indicating reduced virulence 5

Diagnostic Value

The characteristic blue-green color of P. aeruginosa has important diagnostic value:

• Helps in rapid presumptive identification in clinical specimens and cultures
• Different morphotypes of P. aeruginosa (mucoid, smooth, rough, dwarf) may all produce the pigment but can differ in antibiotic susceptibility patterns 1
• Regular monitoring with microbiological cultures is recommended for patients at risk, such as those with cystic fibrosis 6

Clinical Implications

P. aeruginosa infections, identifiable by their characteristic color, have significant clinical implications:

• In cystic fibrosis patients, chronic P. aeruginosa infection leads to more frequent exacerbations and faster decline in pulmonary function 6
• Early identification and treatment of P. aeruginosa colonization is critical, as untreated infections can progress to chronic infection in 80% of cases within 7 years 6
• The European Respiratory Society recommends separating CF patients with and without P. aeruginosa infection to prevent cross-infection 6

The distinctive blue-green color of P. aeruginosa serves as an important visual cue for clinicians and microbiologists, facilitating rapid identification and appropriate management of infections caused by this significant opportunistic pathogen.