Determination of the susceptibility of onychomycosis agents isolated in Sakarya to octenidine dihydrochloride and hypochlorous acid

The aim of this study was to investigate the susceptibility of onychomycosis agents to octenidine dihydrochloride (OCT-D) and hypochlorous acid (HOCl) antiseptics using agar dilution, tube dilution, and flow cytometry methods. In this study, onychomycosis agents including dermatophytes (Trichophyton spp., Microsporum spp., Candida spp.) and secondary agents such as Aspergillus niger and Fusarium solani were cultured on Sabouraud dextrose agar (SDA). Species identification was confirmed using MALDI-TOF MS. The minimum inhibitory concentration (MIC) values of OCT-D, HOCl, and terbinafine for dermatophytes grown on culture plates were determined using the agar dilution method and the broth microdilution (tube dilution) method in accordance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Following MIC determination, the minimum fungicidal concentration (MFC) was assessed. Based on the MFC results, flow cytometry analysis was performed using SYTO 9 and propidium iodide (PI) dyes to investigate the fungicidal effects of OCT-D, HOCl, and terbinafine.As a result of antifungal susceptibility testing of onychomycosis agents, approximate MIC values obtained by the agar dilution method were 250 mg/L for OCT-D, 128 mg/L for HOCl, and 0.064 mg/L for terbinafine. Using the tube dilution method, approximate MIC values were 62.5 mg/L, 64 mg/L, and 0.032 mg/L for OCT-D, HOCl, and terbinafine, respectively. Flow cytometry-based viability analyses showed that the results obtained using the tube dilution method were more consistent. Since OCT-D and HOCl demonstrated MIC values far below their commercially available concentrations and exhibited high fungicidal activity, further studies suggest that these agents may be strong alternatives for topical treatment.