In Vitro and In Vivo Antifungal Efficacy and Safety of the CaDef2.1G27‑K44 Peptide against the Neglected and Drug-Resistant Pathogen Candida krusei.

The growing threat of fungal infections, driven by increasing drug resistance, has become a major global health concern. Candidiasis, a common human infection, is associated with high mortality, particularly in invasive cases. Among non-albicans Candida (NAC) species, Candida krusei (renamed Pichia kudriavzevii) is of clinical importance because of its intrinsic resistance to fluconazole, complicating treatment options. This study evaluated the antifungal efficacy and safety of the bioinspired peptide CaDef2.1G27‑K44 (CDF-GK) against NAC species, with a specific focus on C. krusei, through a series of in vitro and in vivo tests. CDF-GK effectively inhibited the growth of several yeast species, including C. glabrata, C. guilliermondii, C. bracarensis, and C. nivariensis, with MIC values ranging from 3.12 to 200 μM. The peptide demonstrated particularly strong activity against C. krusei, with an MIC100 of 25 μM, an MFC100 of 50 μM, and an IC50 of 5 μM, surpassing the effectiveness of fluconazole. Additionally, CDF-GK inhibited biofilm formation, caused 100% cell death within 1 h, permeabilized the cell membrane, interacted with ergosterol, induced oxidative stress, mitochondrial dysfunction, and vacuolar fragmentation, and entered the intracellular space of C. krusei. In vivo assays using Galleria mellonella larvae confirmed the low toxicity of CDF-GK, even at high concentrations, and significantly improved the survival of infected larvae with minimal activation of cellular and humoral immune responses. These findings indicate that CDF-GK holds great promise as a therapeutic agent for C. krusei infections, as it combines potent antifungal action with safety in both in vitro and in vivo models.