Phenylalanine-based antimicrobial peptides show activity against otomycosis-causing *Aspergillus terreus* AT-1 and yeast pathogens

Fungal infections are a growing public health concern, with otomycosis representing a persistent superficial disease often complicated by recurrence and treatment failure. This is largely due to insufficient genomic characterization of causative species and undefined susceptibility profiles. Current antifungal therapies face challenges with resistance and limited efficacy. Antimicrobial peptides (AMPs) offer a promising alternative due to their broad-spectrum activity and novel mechanisms, yet their rational design often lacks integrated efficacy, biosafety, and mechanistic endpoints. This study addresses the gap by linking clinical isolation and genomic analysis to informed AMP design.

Researchers isolated and performed whole genome sequencing on an Aspergillus terreus AT-1 strain from a patient with otomycosis, comparing it to controls. Genomic analysis included targeted investigation of cytochrome P450 families, secondary metabolite biosynthetic gene clusters, pathogenicity resources, and antimicrobial resistance signatures. Subsequently, they rationally designed five C-terminally amidated, phenylalanine based short peptides with controlled physicochemical parameters. Antifungal activity was assessed using broth microdilution MIC assays against A. terreus AT-1 and yeast pathogens. Hemolysis testing evaluated biosafety, while propidium iodide based flow cytometry and microscopy determined membrane permeabilization.

Clinical otoscopy confirmed otomycosis, with culture yielding A. terreus AT-1 from the affected ear, absent in controls. Genome annotation of A. terreus AT-1 revealed a functionally diverse repertoire encompassing metabolism, transport, secondary metabolism, pathogenicity-linked features, and a structured resistance gene landscape. The rationally designed peptide panel demonstrated measurable antifungal activity against A. terreus AT-1 and various yeast pathogens. Distinct hemolysis profiles were observed across the peptide panel, suggesting varying levels of host cell toxicity, which is crucial for biosafety considerations in therapeutic development. While specific quantitative MIC values or percentages of inhibition were not detailed in the abstract, the qualitative finding of "measurable antifungal activity" across the panel is a key outcome. This indicates the potential for these novel peptides to inhibit fungal growth. The study also provided mechanistic insight into how these peptides exert their effects.

Specifically, peptide C3 significantly increased A. terreus AT-1 conidial membrane permeability, indicating a direct fungicidal mechanism.