(Poly)phenolics are plant secondary metabolites, regularly consumed by humans (∼1 g/day) in the form of fruits, vegetables and beverages (tea, coffee, wine and juices)( Reference Augustin and Gary 1 ). They are thought to be protective against infectious and degenerative diseases via their antioxidant, anti-inflammatory and antimicrobial activities( Reference Stefano and Crispian 2 ). In recent years, the potential antimicrobial activity of (poly)phenolics has attracted increasing scientific attention, partially due to development of microbial resistance to commonly used antimicrobial agents. Candida albicans, an opportunistic fungal pathogen, is one of the major causes of life threatening, invasive candidiasis with estimated mortality rate of 46–75%( Reference Brown 3 ). The ability of C. albicans to grow as a ‘biofilm’ and its flexibility in adapting to different environmental conditions contributes to unacceptably high rates of morbidity and mortality, of which ineffectual antifungal therapy is a key factor. Therefore, alternative approaches to prevent biofilm formation or destruction and modulation of established biofilms are highly desirable. The aim of the present study was to evaluate the potential role of (poly)phenolics, in the prevention, and possibly management, of chronic oral and systemic fungal infections.
(Poly)phenolics (n = 14), belonging to two major groups (flavonoids and non-flavonoids) were examined against C. albicans isolates (n = 20). Planktonic minimum inhibitory concentrations (PMIC) were determined using the CLSI M-27A broth microdilution method, while sessile MIC was determined by XTT reduction metabolic assay. The most active (poly)phenolic molecules were further tested for their role in preventing C. albicans biofilm formation and disruption of mature biofilms (biomass assays); their effect on C. albicans morphology and gene expression was assessed through light microscopy and qPCR.
Of 14 (poly)phenolics tested, seven (curcumin, pyrogallol, pyrocatechol, quercetin, gallic acid, caffeic acid, naringenin) were effective inhibitors of planktonic growth of C. albicans, while 3,4-dihydroxyphenylacetic acid, epigallocatechin, epigallocatechin gallate, hesperetin, malvidin, pelargonidin, and apigenin had no discernible effect at the highest test concentration. PMIC was lowest for pyrogallol (80 μg/mL) followed by curcumin (100 μg/mL). These two compounds also displayed potent activity against C. albicans biofilms (SMIC50 = 40 & 50 μg/mL, respectively). SMIC50 concentration of curcumin and pyrogallol significantly inhibited C. albicans biofilm growth when added 0, 1 and 2 h post adhesion (p < 0.001). However decrease in biomass was not significant when curcumin and pyrogallol were added at 24 h. In addition, overnight coating of coverslips with SMIC50 concentration of curcumin and pyrogallol caused 58% and 15% reduction in initial adhesion of yeast cells to the coverslips. Light microscopy images of curcumin treated cells showed inhibition of hyphal growth, at different treatment points (0, 1, 2, 4 h). qPCR analysis showed differential expression of genes responsible for C. albicans adhesion, hyphal growth and elongation following curcumin treatment.
Overall there was a promising antifungal activity and inhibition of biofilm formation by curcumin and pyrogallol. Cellular and in-vivo studies are necessary to explore their use in the prevention and management of fungal infections.
