112 | Environmental isolation and genetic characterization of first Italian Candida blankii strains: an emerging pathogen

Gabriele Parrino¹, Alessia Billè¹, Lucilla Lo Re¹, Bianca Bauso¹, Francesco Mediati¹, Kyrylo Oleksandrovych Hnezdilov¹, Domenico Davide Anania¹, Gabriele Rigano^2|3, Letterio Giuffrè¹, Giuseppe Criseo¹, Orazio Romeo¹ | ¹Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, Italy; ²Department of Biology, University of Rome “Tor Vergata”, Rome, Italy; ³PhD programme in Space Science and Technology, Department of Physics, University of Trento, Italy.

In recent years, there has been a marked increase in infections caused by non-albicans Candida species, a diverse group of ascomycetous yeasts often characterized by complex antifungal resistance profiles that complicate patient management. This shift has prompted a reevaluation of the clinical significance of species once considered rare or marginal. Among them, Candida blankii (today Tardiomyces blankii) has recently emerged as a potential opportunistic pathogen capable of causing invasive infections and displaying reduced susceptibility to both azoles and echinocandins, the primary antifungal agents used in clinical practice. Despite its growing clinical relevance, little is known about the ecological distribution of C. blankii, its virulence mechanisms, or the genetic determinants underlying antifungal resistance. In this context, environmental studies aimed at identifying potential reservoirs of the fungus represent a crucial step toward understanding transmission pathways and anticipating future public health threats. In this study, to investigate the presence of pathogenic Candida spp. in the urban environment, we analyzed a total of 102 soil samples, collected between October 2024 and May 2025, from the areas surrounding Lake Ganzirri and Lake Faro, as well as along the northern coast of Messina. The mycological investigation resulted in the identification of 27 fungal species, including several of clinical relevance, and led to the isolation of five environmental strains of C. blankii. All C. blankii strains were subjected to Illumina next-generation sequencing (NGS), yielding over 87 million high-quality reads (over 17 million reads for each strain). Reads were assembled using SPAdes and further refined with Redundans, resulting in genomes of approximately 14.4 Mbp with >95% completeness. Gene annotation identified over 6,100 genes per strain, and pangenomic analysis revealed a high level of gene conservation, with 87% of orthogroups classified as core. Phylogenomic analysis revealed two main clusters, one of which comprised all Sicilian environmental strains isolated in this study. Analysis of genes associated with antifungal resistance (FKS1, ERG11, ERG9, ERG6, and TAC1b) showed high homology with known sequences and no canonical mutations linked to drug resistance, although multiple copies of the ERG11 and FKS1 genes were detected, potentially contributing to antifungal tolerance. This study reports, for the first time, the presence of C. blankii in Messina, Sicily and provides novel ecological, genetic, and genomic insights into this emerging species. Our findings underscore the need for integrated environmental surveillance and molecular monitoring within a One Health framework to enable the early detection of emerging fungal pathogens and mitigate risks to human and animal health.