Molecular identification and antifungal susceptibility of otomycosis agents in Shiraz, Iran: predominance of Aspergillus tubingensis

Otomycosis is a common external auditory canal infection, frequently caused by Aspergillus and Candida species. Diagnostic limitations and species-dependent antifungal susceptibility contribute to recurrence and treatment challenges. This study aimed to determine species distribution and antifungal susceptibility patterns of otomycosis isolates in southern Iran. A cross-sectional study enrolled 104 patients with confirmed otomycosis (November 2018–March 2019). Molecular identification was performed by β-tubulin sequencing (molds) and ITS region sequencing (yeasts). Antifungal susceptibility testing against fluconazole, posaconazole, miconazole, terbinafine, amphotericin B, and nystatin followed CLSI microdilution methods (M38-Ed3 and M27-Ed4). Among 104 patients, 55% were female, and nearly half were aged 40–60 years. Itching (81.7%), inflammation (80%), and otorrhea (74%) were predominant symptoms. Cultures yielded 102 mold and 16 yeast isolates. Microscopic observation identified the A. niger complex as the predominant agents, while sequencing confirmed A. tubingensis (36.3%) and A. niger (28.4%) as the main species causing otomycosis. C. albicans and C. parapsilosis were the most frequent yeasts. Posaconazole and amphotericin B showed potent activity against most Aspergillus isolates, and 12 of the 16 Candida isolates (75%) remained fluconazole-susceptible. Molecular techniques significantly improved the accuracy of species identification of otomycosis agents, revealing a high frequency of A. tubingensis in this study population. Posaconazole and amphotericin B showed strong in vitro activity, while fluconazole showed limited efficacy against molds. Overall, continuous molecular surveillance is essential to guide optimal antifungal therapy and prevent resistance.