Diutina cutanea sp. nov.-phylogenomic-based analysis of a novel clinically relevant ascomycetous yeast.

Abstract

Ascomycetous yeasts of the genus Diutina are rarely encountered in clinical routine diagnostics, but known to harbor species with decreased susceptibility to azole antifungals. This study describes a clinical strain representing a novel member of the genus Diutina, which we named Diutina cutanea. The clinical strain, isolated from a human foot wound, was molecularly identified by ITS/D1D2 ribosomal DNA sequencing. Extensive phenotypic characterization was done by culturing, microscopy, sporulation assays, assimilation tests, and antifungal susceptibility testing. Nanopore sequencing was performed for de novo genome assembly and comparative genomics. ITS/D1D2 ribosomal DNA sequencing resulted in a low identity score compared to other Diutina species. Morphological characterization showed round to oval cells of 2-3 × 3-8 µm in size, multilateral budding, and formation of pseudohyphae were observed. Colonies were white, glossy, smooth, butyrous, and had an entire margin. Growth on CHROMagar Candida Plus allowed phenotypic distinction between D. cutanea and related clinically relevant species. Antifungal susceptibility showed an elevated fluconazole MIC of 4 µg/ml. Genome sequencing placed D. cutanea distantly but basal to the non-pathogenic relatives D. scorzettiae, D. ranongensis, and D. siamensis. ANI analysis resulted in a pairwise similarity of 0.83-0.86 between D. cutanea and its relatives. In conclusion, phylogenomic and ANI analyses showed D. cutanea to be a unique taxon within the genus Diutina. Diutina cutanea can be reliably phenotypically discerned from other clinically relevant Diutina species by culturing on CHROMagar Candida Plus.