Photodynamic inactivation by hypericin-P123 on azole-resistant isolates of the Trichophyton rubrum complex as planktonic cells and biofilm

Abstract

Introduction: The Trichophyton rubrum complex comprises the majority of dermatophyte fungi (DM) responsible for chronic cases of onychomycosis, which is treated with oral or topical antifungals. However, owing to antifungal resistance, alternative therapies, such as photodynamic therapy (PDT), are needed. This study investigated the frequency of the T. rubrum species complex in onychomycosis cases in the northwestern region of Paraná state, Brazil, and evaluated the efficacy of (PDT) using P123-encapsulated hypericin (Hyp-P123) on clinical isolates of T. rubrum in the planktonic cell and biofilm forms.

Material and methods: The frequency of the T. rubrum complex in onychomycosis cases from 2017 to 2021 was evaluated through a data survey of records from the Laboratory of Medical Mycology (LEPAC) of the State University of Maringa (UEM). To determine the effect of PDT-Hyp-P123 on planktonic cells of T. rubrum isolates, 1 × 10⁵ conidia/mL were treated with ten different concentrations of Hyp-P123 and then irradiated with 37.8 J/cm². Antibiofilm activity of PDT-Hyp-P123 was tested against T. rubrum biofilm in the adhesion phase (3 h), evaluated 72 h after irradiation (37.8 J/cm²), and the mature biofilm (72 h), evaluated immediately after irradiation. In this context, three different parameters were evaluated: cell viability, metabolic activity and total biomass.

Results: The T. rubrum species complex was the most frequently isolated DM in onychomycosis cases (approximately 80 %). A significant reduction in fungal growth was observed for 75 % of the clinical isolates tested with a concentration from 0.19 μmol/L Hyp-P123, and 56.25 % had complete inhibition of fungal growth (fungicidal action); while all isolates were azole-resistant. The biofilm of T. rubrum isolates (TR0022 and TR0870) was inactivated in both the adhesion phase and the mature biofilm.

Conclusion: PDT-Hyp-P123 had antifungal and antibiofilm activity on T. rubrum, which is an important dermatophyte responsible for onychomycosis cases.

Keywords: Antifungal drug resistance; Biofilm; Onychomycosis; Photodynamic inactivation; Trichophyton infection.