Phenotypic, antifungal susceptibility, and molecular characterization of an Actinomucor elegans clinical isolate: first characterized record in Chile

Background Invasive fungal infections (IFIs), particularly mucormycosis, represent life-threatening complications in severely immunocompromised patients. Early species-level identification and characterization of unusual opportunistic pathogens are essential for expanding epidemiological knowledge and guiding targeted antifungal management. Methods We performed a polyphasic characterization combining histopathology, micromorphological evaluation, internal transcribed spacer (ITS) rDNA sequencing, phylogenetic analysis, and broth microdilution antifungal susceptibility testing of a clinical isolate of Actinomucor elegans (ChFC 20) recovered from a rhinosinusal tissue biopsy of an immunocompromised pediatric oncology patient in Chile. Results Histopathological examination of tissue biopsy sections revealed broad, pauciseptate, ribbon-like hyphae demonstrating direct tissue invasion. The isolate grew rapidly on potato dextrose agar, producing characteristic cottony, whitish-yellow colonies with verticillate sporangiophores and non-apophysate sporangia. ITS sequencing confirmed species-level identification as Actinomucor elegans with 99% identity. In vitro susceptibility testing demonstrated low minimum inhibitory concentrations (MICs) for amphotericin B (1 µg/mL), itraconazole (1 µg/mL), isavuconazole (0.5 µg/mL), and posaconazole (0.5 µg/mL). Targeted therapy with liposomal amphotericin B combined with surgical debridement resulted in complete clinical clearance. Conclusion This study provides the first comprehensive phenotypic, antifungal susceptibility, and molecular characterization of an invasive Actinomucor elegans clinical isolate from Chile, underscoring the critical role of integrating histopathology with molecular phylogenetics in resolving rare mucoralean pathogens.