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

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.

UHPLC‐HRMS/MS Based Profiling of Algerian Lichens and Their Antimicrobial Activities

“…[56] Although many lichens have been widely investigated for their antibacterial compounds, less is known about antifungal lichenic metabolites. [6] When comparing the nature of the main compounds detected in each cyclohexane active extracts, i) aliphatic acids such as rangiformic, jackinic and roccellic acids were abundant in CR1; ii) depsides (e.g., evernic, sekikaic and homosekikaic acids) and the well-known usnic acid were the main metabolites in RF1 and RTa1; iii) although RP1 was characterized by the presence of roccellic acid as the major compound, orselinic acid was also present at a moderate percentage. [57] [58] Lichenic substances have seldom been identified as exhibiting some antifungal activities.…”

“…[1] Lichens are very slow-growing organisms (growth rate: few mm/year) that can bud with low supply of nutrients and that are able to survive periodic desiccation. Thanks to their particular organization, described as a 'complex community', [6] they could provide a number of unique secondary metabolites. [2] In fact, some lichen species present extreme survival capability and develop even in hostile environments, e.g., when exposed to drought, to extreme temperatures or to high UV radiations.…”

“…[15] [16] Lichenic study now benefits from the latest progresses in analytical techniques. [6] [9][21] [22] Until recently, the Algerian lichen diversity only prompted little attention, even given its potential interest. [17] Direct analysis in real timemass spectrometry (DART-MS) constitutes one of the latest innovations in the investigation of lichenic secondary metabolites.…”

“…[3 -5] Since the past decade, several biological activities have been attributed to lichens and to their metabolites. Thanks to their particular organization, described as a 'complex community', [6] they could provide a number of unique secondary metabolites. They include aliphatic, aromatic, mycosporine as well as terpenic compounds displaying a variety of roles ranging from plant growth inhibitors and insecticides to enzymes inhibitors and photoprotective agents.…”

“…[18] Given those technological improvements and their metabolic potential, lichens constitute the subject of renewed interest from scientists and are more and more investigated into details to source new interesting and valuable substances. [6] [9][21] [22] Until recently, the Algerian lichen diversity only prompted little attention, even given its potential interest. In fact, a recent literature survey established that it accounts some 1085 species (among which 64 are endemic) grouped into 187 genera and 73 families, figures that could drastically evolve with the forthcoming 'Checklist of Algerian Lichens' and the exploration of areas where the biodiversity was not or only poorly studied.…”