A study of patients with fungal ear canal infections in southern Iran has identified Aspergillus tubingensis as the most common causative organism, a finding the authors say would likely have been missed without genetic sequencing. The cross-sectional research, published in Nature, enrolled 104 people with confirmed otomycosis in Shiraz between November 2018 and March 2019 and was carried out by investigators at Shiraz University of Medical Sciences together with a collaborator at the Medical University of Vienna.
Why it matters
Otomycosis — a fungal infection of the external auditory canal — is a familiar and often stubborn clinical problem, and the paper notes that gaps in diagnosis and differences in how individual fungal species respond to drugs both contribute to cases that come back after treatment. Because standard laboratory culture and microscopy can struggle to separate closely related molds, the species actually responsible may go unrecorded, and with it the drug profile that would guide therapy. According to Nature, the Shiraz team's results suggest that routine visual identification can mislead clinicians about which organism they are dealing with.
What the patients looked like
Just over half of the participants were women, and close to half fell in the 40 to 60 age bracket. The symptoms reported most often were itching, cited by 81.7% of patients, followed by inflammation at 80% and discharge from the ear at 74%.
Laboratory work produced 102 mold isolates and 16 yeast isolates from the group. When the researchers examined the molds under a microscope, organisms belonging to the A. niger complex appeared to dominate. Sequencing told a different story. Using β-tubulin gene sequencing for the molds and ITS region sequencing for the yeasts, the team found that A. tubingensis accounted for 36.3% of cases and A. niger for 28.4%, making them the two principal agents of infection in the cohort. Among the yeasts, Candida albicans and Candida parapsilosis were the most frequently recovered.
The gap between what microscopy suggested and what sequencing confirmed is central to the paper's argument. The authors report that molecular methods substantially sharpened the accuracy of species-level identification and brought the high frequency of A. tubingensis into view — a prevalence that conventional observation of the A. niger complex would not have distinguished.
Drug susceptibility results
The team tested the isolates against six antifungals — fluconazole, posaconazole, miconazole, terbinafine, amphotericin B and nystatin — using CLSI microdilution protocols, specifically the M38-Ed3 and M27-Ed4 standards.
Posaconazole and amphotericin B performed strongly against the great majority of Aspergillus isolates in the laboratory setting. Fluconazole, by contrast, showed only limited activity against the molds. Among the 16 Candida isolates, 12 — three-quarters of the total — remained susceptible to fluconazole.
The authors conclude that ongoing molecular surveillance is needed to steer antifungal treatment choices and to head off resistance. The work was funded by Shiraz University of Medical Sciences under grant numbers 16505 and 23293, and the study protocol was cleared by the university's ethics committee under two separate approvals, one covering sample collection and molecular identification and the other covering susceptibility testing. The paper is published open access under a Creative Commons Attribution-NonCommercial-NoDerivatives licence.
What to watch: whether similar sequencing surveys in other regions turn up the same hidden dominance of A. tubingensis, which would argue for molecular identification becoming standard in recurrent ear canal infections rather than an optional extra.
