Pseudomonas aeruginosa pyocyanin and 1-hydroxyphenazine inhibit fungal growth

Aim: To examine strains of Pseudomonas aeruginosa for specific Antifungal factors.

Methods: Two clinical strains of P aeruginosa with strong in vitro inhibition (by cross streak assay) of Candida albicans and Aspergillus fumigatus were examined. Both strains were isolated from sputum--one from a patient with cystic fibrosis and one from a patient with bronchiectasis. Bacterial extracts were fractionated by high performance liquid chromatography and examined by ultraviolet absorbance and mass spectroscopy. Antifungal activity against C albicans and A fumigatus was determined in a well plate assay.

Results: Pyocyanin was the major Antifungal agent of P aeruginosa; 1-hydroxy-phenazine also possessed activity. Pyocyanin MICs for C albicans and A fumigatus were > 64 micrograms/ml. These phenazines were active against nine other yeast species pathogenic for man. Preliminary experiments also suggested possible inhibition of yeast mycelial transformation in C albicans by pyocyanin.

Conclusions: There may be a role for pyocyanin and 1-hydroxyphenazine in the prevention of pulmonary candidiasis in patients colonised by P aeruginosa.