Antifungal and Anti-Biofilm Activities of Acetone Lichen Extracts against Candida albicans

Marion Millot,Christine Imbert,Lucile Dutreix,Marion Girardot,Lengo Mambu

doi:10.3390/molecules22040651

Abstract

Candida albicans is a commensal coloniser of the human gastrointestinal tract and an opportunistic pathogen, especially thanks to its capacity to form biofilms. This lifestyle is frequently involved in infections and increases the yeast resistance to antimicrobials and immune defenses. In this context, 38 lichen acetone extracts have been prepared and evaluated for their activity against C. albicans planktonic and sessile cells. Minimum inhibitory concentrations of extracts (MICs) were determined using the broth microdilution method. Anti-biofilm activity was evaluated using tetrazolium salt (XTT) assay as the ability to inhibit the maturation phase (anti-maturation) or to eradicate a preformed 24 h old biofilm (anti-biofilm). While none of the extracts were active against planktonic cells, biofilm maturation was limited by 11 of the tested extracts. Seven extracts displayed both anti-maturation and anti-biofilm activities (half maximal inhibitory concentrations IC50_mat and IC50_biof ≤ 100 µg/mL); Evernia prunastri and Ramalina fastigiata were the most promising lichens (IC50_mat < 4 µg/mL and IC50_biof < 10 µg/mL). Chemical profiles of the active extracts performed by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) have been analyzed. Depsides, which were present in large amounts in the most active extracts, could be involved in anti-biofilm activities. This work confirmed that lichens represent a reservoir of compounds with anti-biofilm potential.

Highlights

Lichens are symbiotic organisms resulting from the association between a fungus, called the mycobiont, and photoautotrophic partners, green algae, and/or cyanobacteria, called the photobiont
Extracts have been analyzed by thin layer chromatography (TLC) in two system solvents and observed under ultraviolet (UV) and after spraying anisaldehyde sulfuric reagent and/or by high performance liquid chromatography (HPLC)
Polyphenolic compounds and terpenoids predominated in the chemical profiles of the studied lichen extracts, with often one or two major metabolites (Table 1 and Supplemental Figure S1)

Summary

Introduction

Lichens are symbiotic organisms resulting from the association between a fungus, called the mycobiont (usually an ascomycete), and photoautotrophic partners, green algae, and/or cyanobacteria, called the photobiont. A third partner embedded in the lichen cortex was identified as a basidiomycete yeast [1]. The lichen thallus is a support for other microorganisms living inside and outside the thallus, including endo- and epi-lichenic fungi and bacteria [2,3] Interactions exist within this complex ecosystem and many of the molecules that make up this chemical environment are involved in interactions between the community members influencing overall community homeostasis and survival. C. albicans is an opportunistic yeast causing superficial and invasive infections, especially among elderly and/or frail patients

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