In vitro photodynamic inactivation of orofaringeal Candida spp. by α-terthienyl isolated from Porophyllum obscurum (Spreng) DC (Asteraceae)

POSTIGO A; PETENATTI E; ZACCHINO S; SORTINO M

Puerto Varas

Simposio; VIII Simposio Internacional de Química de Productos Naturales y sus Aplicaciones; 2014

Photodynamic therapy constitutes an alternative to conventional antifungal treatments, based on the utilization of compounds that inhibit or kill microorganisms only under the effect of light, process known as Photodynamic Inactivation. Porophyllum obscurum is an aromatic sub-shrub, commonly known as "Yerba del venado" that inhabits the central and northern regions of Argentina. In previous works we found that P. obscurum hexanic extract showed photoactivity against Candida albicans ATTC 10231 under the influence of UV-A light. Bioassay-guided fractionation of this extract for antifungal activity with bioautography and microdilution assays with UV-A light irradiation, led to the isolation of α-terthienyl (α-T) as the main active component of this extract. The optimal values of two variables, exposure irradiation time (ET) and distance to the irradiation source (DIS) were established against a panel of clinical Candida spp. strains (C. albicans, C. tropicalis, C. parapsilosis and C. krusei) isolated from patients with oropharyngeal candidiasis (OPC), by employing Design Expert Software (DES). Results showed that the optimal values of ET and DIS were 5 min and 6.06-6.43 cm with a Desirability factor of 0.989. In addition, time-kill assays and confocal microscopy after vital staining could demonstrate that α-T plus UV-A light, at the optimal conditions, caused a complete reduction of viable cells in 5 min. In another set of experiments, it could be demonstrated that the germ tube formation of C. albicans was inhibited by sub-inhibitory concentrations of α-T. These data provide evidence that α-T plus UV-A light could constitute an alternative for OPC treatments at the optimal conditions determined with DES.