Comparison of antifungal activity of natural prenylated flavanones against Candida albicans biofilms.

MARIANA PERALTA, MARÍA ANGEL DA SILVA, MARÍA GABRIELA ORTEGA, JOSÉ LUIS CABRERA, MARÍA GABRIELA PARAJE.

Córdoba

Congreso; XI Congreso Argentino de Microbiología General (SAMIGe) 2015 - Córdoba; 2015

Sociedad Argentina de Microbiología General

The formation of biofilms is an important virulence factor that allows C. albicans to cause many typesof infections and is responsible for most cases of candidiasis at both mucosal and systemic sites. Ithas been reported that Candida biofilms are 30-2000 times more resistant to several antifungal agentscompared to their planktonic (or free-living) counterparts. The continuing emergence of infections withantifungal resistant Candida strains requires a constant search for new antifungal drugs, with the plantkingdom being an important source of chemical structures. Objective: The present study comparedthe antifungal effect of a new prenylated flavanones of Dalea boliviana Britton(2S)-5,7,2-trihydroxy-5-(1,1-dimethylallyl)-8-prenylflavanone (1) and(2S)-5,7,2-trihydroxy-8,3-diprenylflavanone (2) and a natural prenylflavonoid D. elegans(2,4-dihydroxy-5-(1,1-dimethylallyl)-8-prenylpinocembrin-8PP), on Candida albicans biofilms, andcompared this with an azole antifungal (fluconazole). Material and Methods: The fluconazolesensitive (SCa) and azole-resistant (RCa) C. albicans strains were used, with biofilm formation beingstudied using crystal violet (CV) and confocal scanning laser microscopy (CSLM). The minimalinhibitory concentration for sessile cells (SMIC) was defined as the concentration of antifungal thatcaused a 50% (SMIC 50) and 80% (SMIC 80) reduction of treated biofilms. Biofilms were grown ondisks and examined by CSLM using Calcofluor-White, a UV-excitable dye that binds chitin andbeta-glucan, which has long been used to highlight fungal cell walls.Our results show that 8PP has similar pronounced antibiofilm effects against sensible and resistant C.albicans strains. While the flavonoid (8PP) concentration is higher than the antifungal of a comparativereference (fluconazole), the biofilm formation was strongly inhibited (>85%) by 8PP at 100 mM.It wasobserved that the cellular viability of biofilms decreased with increased concentration of thecompounds assayed, with the results showing a correlation between the CV assay and CFU/ml. Thehazy biofilm appearance was due to diffuse staining of the extracellular material with Calcofluor-White,and implies that this material was composed of mainly cell-wall-like polysaccharides. In theantifungal-treated C. albicans biofilm, the majority of C. albicans cells were present as blastospores(yeast forms) attached to the surface of the disk, which appeared as a haze-like film covering thefungal microcolonies. Biofilms treated with 8PP showed a significantly reduced thickness, with cellsbeing fewer and of less density compared to those of the untreated control (p < 0.001). Similar imageswere obtained with fluconazole.Conclusion: Our data suggest that 8PP may be useful for the treatment of biofilm-related Candidainfections, 8PP may also have a therapeutic potential in C. albicans infections. Further studies are stillnecessary in order to increase the understanding of the mechanisms of antibiofilm activity of thiscompound.