Virulence Assessment of Sporothrix Species from Clinical and Environmental Clades Using Tenebrio molitor as an Experimental Model

Sporotrichosis is a neglected subcutaneous mycosis, globally distributed, caused by thermal dimorphic Sporothrix species. Despite their pathogenic potential in vertebrates, the virulence mechanisms underlying the interaction of these fungi with other groups of organisms remain poorly understood. The present study utilized the coleopteran insect Tenebrio molitor as an experimental model to assess the virulence of seven Sporothrix species belonging to the clinical (Sporothrix brasiliensis, Sporothrix schenckii, Sporothrix globosa, and Sporothrix luriei) and environmental (Sporothrix pallida, Sporothrix mexicana, and Sporothrix chilensis) clades. Larvae were inoculated with conidia or yeast cells and evaluated for survival, fungal burden (colony forming units), histopathology, hemocyte count, and expression of antimicrobial peptide genes. The virulence patterns in this model mirrored those observed in mammalian models for Sporothrix species from the clinical clade, with S. schenckii and S. brasiliensis exhibiting higher virulence (larvae survival rate 30-40%). Furthermore, the study revealed distinct virulence profiles between the mycelial and yeast phases of the fungi, with the yeast phase generally associated with increased virulence. However, contradicting previous findings, in the murine model, the environmental clade species S. pallida and S. chilensis displayed unexpectedly high virulence in their mycelial phase in T. molitor (larvae survival rate of 30% and 10% respectively). Also, the expression profile of AMP genes (Thamatin-like 1 and Tenecin 3) was similarly higher for those larvae infected with S. brasiliensis and S. pallida. These results indicate that the immune response to Sporothrix species in this invertebrate model may also have been shaped by the natural history of coleopteran insects and the Sporothrix genus. Our study highlighted the complex interplay between fungal virulence, host immune response, and ecological factors in shaping the outcome of Sporothrix infections in T. molitor.