Antifungal activity of medicinal and edible homologous polysaccharides and the mechanism.

The purpose of this study was to screen for polysaccharides with antifungal activity from medicinal and edible polysaccharides. We used Caenorhabditis elegans Candida albicans-infection model to screen for three kinds of polysaccharides with antifungal effects, identifying Astragalus membranaceus polysaccharide (AMP) for further analysis. AMP-2, in particular, exhibited good antifungal activity, with total sugar content of 73.31 ± 0.77 %, uronic acid content of 14.03 ± 0.13 %, and sulphate content of 4.81 ± 0.09 %. AMP-2 (molecular weight, 255.927 kD) comprises rhamnose, glucose and galactose, and contains the following bonds 1 →; 1 → 2; 1 → 3; 1 → 4; 1 → 6; 1 → 2, 3; 1 → 2, 4; 1 → 2, 6; 1 → 3, 4; 1 → 3, 6 and 1 → 4, 6. In vitro, AMP-2 was unable to kill fungi. In vivo, AMP-2 enhanced nematode immunity, thus achieving antifungal effects. In pmk-1 mutant nematodes, western blotting revealed that AMP-2 activated the p38 mitogen-activated protein kinase (MAPK) signalling pathway through pmk-1, reducing the number of fungal colony-forming units (CFU) and ROS levels in the infected nematodes and prolonging their lifespan. These findings suggest that AMP-2 is an effective and safe antifungal agent that can be developed into a new antifungal drug.