Antifungal susceptibility profiles of otomycosis etiological agents in Ahvaz, Iran

Otomycosis is a secondary ear fungal infection among predisposed individuals in humid conditions. Aspergillus species are the most common etiologic agents of this infection. Several ototopical antifungals are currently used for the treatment of this disease; however, recurrence and treatment failure are usually observed in some cases. Regarding this, the present study was conducted to investigate the antifungal activity of caspofungin, azoles, and terbinafine against the isolated agents of otomycosis.

This study was conducted on the specimens collected from 90 patients with otomycosis. The samples were cultured on Sabouraud dextrose agar and identified based on morphological characteristics, physiological tests, and microscopic features. Furthermore, the microdilution method was used for antifungal susceptibility testing according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Finally, the minimum inhibitory concentration (MIC) and minimum effective concentration (MEC) ranges, MIC/MEC50, MIC/MEC90, and geometric mean (GM) MIC/MEC were calculated for the isolates.

According to the results, 77 patients with otomycosis were positive for different Aspergillus (88.3%) and Candida (11.7%) species. Aspergillus niger complex (n=36) was found to be the most common agent, followed by A. flavus, A. terreus, and A. nidulans complexes. Furthermore, epidemiological cutoff values (ECVs) were lower than those presented by the CLSI for itraconazole and caspofungin in 98.5% and 42.6% of Aspergillus species, respectively. Terbinafine exhibited a great activity against Aspergillus species, while fluconazole revealed a low activity against both Aspergillus species. Based on the results, 77.8% of Candida species were resistant to caspofungin; however, miconazole and econazole had low MIC ranges.

Aspergillus niger and A. flavus complexes were identified as the most common agents accounting for 85.7% of the isolates. In addition, terbinafine was identified as the best antifungal for both Aspergillus and Candida species. Moreover, tested azoles had relatively low MICs, whereas most of the isolates had the MIC values beyond the caspofungin ECVs.