Photodynamic inactivation of Candida glabrata boosted by association of silver nanoparticles with cationic ZnTE-2-PyP4+ porphyrin

Abstract

Candida glabrata, a high priority fungal pathogen, presents alarming incidence and resistance potential to available antifungals. In this scenario, photodynamic inactivation (PDI) introduces a promising antifungal approach, especially in resistant cases. PDI occurs when a photosensitizer (PS) is excited by an appropriate light source, leading to production of reactive oxygen species (ROS). Zinc porphyrins (ZnPs) are attractive PSs for their efficient ROS generation and cellular uptake. The plasmonic effect of silver nanoparticles (AgNPs) can be explored to potentiate the action of PSs, such as ZnPs, in PDI. Therefore, this work aimed to study the association of AgNPs with ZnTE-2-PyP4+ (ZnP-ethyl) in PDI against C. glabrata. AgNPs were synthesized and characterized by absorption spectroscopy and electron microscopy. The association AgNP:ZnP-ethyl was evaluated by zeta potential (ζ) analyses as well as absorption and emission spectroscopies. The systems containing AgNP:ZnP-ethyl (at different proportions; v/v) and different ZnP-ethyl concentrations (0.5 – 1.5 µM) were prepared and incubated with a resistant isolate of C. glabrata, followed by illumination with a blue LED. The PDI effect was assessed by quantifying colony forming units. AgNPs presented spherical morphology and extinction maximum at ~410 nm, overlapping with the ZnP-ethyl absorption spectra. Variations in ζ confirmed the association between AgNPs and ZnP-ethyl, corroborated by subtle changes in the ZnP spectroscopic profile. The AgNP:ZnP-ethyl systems promoted complete fungal eradication at 0.6 µM, while at 0.5 µM they promoted yeast reduction of ca. 5.7 log10 (1:4; v/v) and 6.8 log10 (4:1; v/v). Illuminated AgNPs had no antimicrobial effect alone, and individual ZnP-ethyl (1.5 µM) promoted a 2 log10 reduction. These results show the benefit of AgNPs:ZnP-ethyl association to boost PDI efficiency against resistant C. glabrata isolates. This is a promising antifungal approach to treat resistant candidiasis.