Antifungal activity of the cationic antimicrobial polymer-polyhexamethylene guanidine hydrochloride and its mode of action

The antifungal activity of polyhexamethylene guanidine hydrochloride (PHMGH) was studied against various pathogenic fungi. PHMGH had more potent antifungal activity than amphotericin B, which is a commonly used antifungal drug, and also showed no hemolytic and lactate dehydrogenase release activities in the range of 1.25–40.0 μg mL⁻¹. PHMGH is a cationic polymer containing an amino group and a polymeric guanidine group. Based on its characteristics such as the cationic charge and hydrophobicity, the antifungal mechanism of PHMGH was investigated using Candida albicans, as a model organism. Flow cytometric contour-plot analysis and microscopy showed changes in the size and granularity of the cells after treatment with PHMGH. A membrane study using 1,6-diphenyl-1,3,5-hexatriene labelling indicated a great loss of phospholipid area in the plasma membrane following PHMGH treatment. To investigate the extent of the damage, fluorescein isothiocyanate-labelled dextran leakage from large unilamellar vesicles was observed, indicating that PHMGH acts on the fungal membranes by inducing pore formation, with the majority of pore size being between 2.3 and 3.3 nm. This mechanism was confirmed with ion transition assays using 3,3′-dipropylthiacarbocyanine iodide and an ion-selective electrode meter, which indicated that membrane depolarization involving K⁺ leakage was induced. Taken together, these results show that PHMGH exerts its fungicidal effect by forming pores in the cell membrane.