Lichen extracts inhibit Candida albicans growth and biofilm formation via cAMP-PKA and Cek1 MAPK signaling pathway

Abstract

The increasing prevalence of Candida infections and growing concerns about antifungal resistance have encouraged research into new therapeutic agents from natural sources. This study investigated the antifungal activity of Dermatocarpon miniatum (L.) W. Mann and Parmelia saxatilis (L.) Ach. lichen extracts against Candida species, focusing on their antibiofilm effects and underlying molecular mechanisms. Methanol and aqueous extracts of both lichens were prepared and evaluated against four reference and 19 clinical Candida strains using microdilution methods. This study employed a multi-modal approach to explore the antibiofilm effect of lichen extracts on Candida albicans, including CCK-8 assay for antibiofilm capacity, qRT-PCR for biofilm-related (cAMP-PKA and Cek1 MAPK pathways) gene expressions, field emission scanning electron microscopy for morphological assessment, and Galleria mellonella infection model for in vivo evaluation. Antifungal susceptibility tests revealed only methanol extracts showed antifungal activity, with minimum inhibitory concentrations ranging from 160 to 2500 μg/mL for P. saxatilis methanol extract (ParM) and 320–2500 μg/mL for D. miniatum methanol extract (DerM). ParM (1250 μg/mL) significantly reduced biofilm formation and down-regulated key genes involved in both pathways. Methanol extracts of lichens disrupted hyphal networks and cell integrity. In the Galleria mellonella model, DerM provided protection similar to fluconazole, while ParM provided 60 % survival. These findings indicate that lichen extracts, particularly ParM, inhibit Candida albicans biofilm formation by downregulating genes in the cAMP-PKA and Cek1 MAPK pathways. Despite the promising antibiofilm and in vivo activities of these extracts, their limited antifungal activity against Candida suggests that further research is needed for their therapeutic potential.