Lichen biodiversity: A source of secondary metabolites active against Candida biofilms

Abstract

The frequency of infections involving fungal biofilms (in particular associated with Candida yeasts) as well as their resistance to current treatments, justified the need to discover new anti-biofilm substances [1]. Lichens correspond to a symbiotic association between an alga and/or a cyanobacteria and a fungus and are a reservoir for novel compounds with therapeutic potential. For these reasons, this research program was focused on the access to original compounds from lichens from the French Limousin region [2]. A screening of forty lichen extracts was performed against planktonic Candida albicans by evaluating MICs. Moreover, the activity of these extracts was studied against the development (up to 48h) of C. albicans biofilms on polystyrene substrates, using the XTT method. These studies showed that none of extracts active against planktonic C. albicans (MIC> 0.1 mg/mL). However, eleven extracts demonstrated a significant anti-biofilm activity (p < 0.05) for concentrations less than 50 µg/mL. Among them, the Cladonia parasitica extract (43 µg/mL at 24h) was selected for further investigation. HPLC analysis showed poor chemical diversity of the extract which contained 72% thamnolic acid. This depside was active against Candida biofilms at 14.5 and 33 µg/mL at 24 and 48h respectively. Among the most active extracts, Evernia prunastri, Ramalina fraxinea, R. fastigiata, Xanthoparmelia conspersa and Peltigera hymenina displayed significant anti-biofilm activity (p < 0.05) for concentrations less than 10 µg/mL; in particular for E. prunastri and R. fastigiata whose activity was observed as soon as 24h and persisted at 48h. This work demonstrated the anti-biofilm activity of lichens from local biodiversity and thamnolic acid against C. albicans and highlighted the potential of lichens to fight Candida biofilms.