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-hydroxyphenazine also possessed activity. Pyocyanin MICs for C albicans and A fumigatus were > 64 mu g/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.