Otomycosis: Main challenging microbial agent causing otitis externa in northern Iran

Abstract Poster session 2, September 22, 2022, 12:30 PM - 1:30 PM Objectives Otitis externa is one of the most common ear diseases, caused by bacterial and fungal agents. Accumulation of epithelial cells, cellular detritus, waxy substances, and microorganisms in the ear canal provide a proper environment for fungal growth, leading to annoying congestion. In this study, we aimed to identify the fungal causative agents and determine their susceptibility to the antifungal drugs were examined. Methods All patients with suspected otitis externa, referred to Amir-al Momenin Referral Centre from October 2020 to November 2021 entered to study. A total of 200 patients’ ear discharge and debris collected samples were examined by direct examination and cultured on SDA supplemented with chloramphenicol. Definitive identification of grown fungi was made by PCR-RFLP and sequencing of ribosomal DNA. In vitro susceptibility testing of the fungal isolates against eleven different antifungal agents was analyzed using the CLSI broth microdilution methods. Results A total of 101 (50.5%) cases were confirmed with otomycosis. Most patients were in their fifth decade of life (n = 35, 34.6%), female (n = 57, 56.4%), and had unilateral ear involvement (n = 78, 77.2%). The most common symptoms were earache (56.4%) and itching (51.4%). Most underlying predisposing factors are overaggressive using cotton swabs (65.3%) and history of topical antibiotics (48.5%). Among the 117 fungal isolates, Aspergillus section Nigri was the most common agent 58 (49.57%), followed by Aspergillus section Flavi 19 (16.23%), C. parapsilosis 14(11.96%), Aspergillus section Fumigati 12 (10.25%), C. orthopsilosis 6 (5.12%), C. albicans complex 5 (4.27%), Mucor spp. 2 (1.71%), and Syncephalastrum spp. 1 (0.85%). Mainly, all tested antifungals were active against the most isolates of Aspergillus, aside from tioconazole, nystatin, and terbinafine, which showed low in vitro effects. Also, nystatin and itraconazole showed higher GM MICs in against all Candida species isolates. Conversely, amphotericin B (GM = 0.07129) in Aspergillus and voriconazole (GM = 0.03686) in Candida showed the highest antifungal activity. Regarding ECV values represented by ECOFFs, one of each A. niger (MIC 8 μg/mL), A. flavus (MIC 2 μg/ml), and A. fumigatus (MIC 2 μg/ml) isolates were resistant to itraconazole. Conclusion In this study, inconsistent with previous ones, fungal agents have overcome bacterial ones as the etiology of otitis externa. This result may relate to misuse or improper use of topical steroids, antibiotics, and inappropriate control of infection. In addition, our sample collection site was an ENT referral center and many patients have been admitted to this center due to treatment failure and suffered from recurrence. Aspergillus section Nigri isolation domination was seen, in agreement with other results. The MICs distribution of Aspergillus species isolates against triazole antifungals are close to ECVs defined by the CLSI and likely outrun it over time. We recommend that physicians request drug susceptibility testing before antibiotic therapy, to prevent the development of resistance.