Antifungal Susceptibility and Clinical Efficacy of Chlorhexidine Combined with Topical Ophthalmic Medications Against Fusarium Species Isolated from Corneal Samples

Kang Min ¹ Yuxuan Wu ¹ Qingquan Shi ² Zhiqun Wang ² Yang Zhang ² Kexin Chen ² Xizhan Xu ² Man Zhou ² QINGFENG LIANG ² Xinxin Lu ^1*

• ¹ Department of Laboratory Medicine,Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, 100005, China., Beijing, China
• ² Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing 100005, China, Beijing, China

This study investigated the susceptibility of various Fusarium fungi to five topical antifungal agents: natamycin, voriconazole, chlorhexidine, natamycin combined with chlorhexidine, and voriconazole combined with chlorhexidine. A total of 194 Fusarium strains isolated from corneal samples were collected from 2013 to 2024 and identified at the species level using mass spectrometry. F. solani, F. oxysporum, and F. keratoplasticum were the main isolates. Minimum inhibitory concentration (MIC) data were collected to guide clinical application. The MIC values for natamycin in F. solani species complex (FSSC) and F. fujikuroi species complex (FFSC) were 2-8 and 2-8 μg/mL, respectively. The MICs for FSSC and FFSC respectively ranged from 0.25-16 and 1-8 μg/mL for voriconazole and 2 to > 16 μg/mL and 1 to > 16 μg/mL for chlorhexidine. The MICs of natamycin were not significantly different between FSSC and FFSC. However, voriconazole, chlorhexidine, natamycin combined with chlorhexidine, and voriconazole combined with chlorhexidine had significantly higher MICs for FSSC compared with FFSC. Compared with voriconazole, voriconazole combined with chlorhexidine exhibited enhancement of antifungal activity against 100% of tested Fusarium strains. Compared with natamycin, enhancement of antifungal activity of natamycin combined with chlorhexidine was 81.4% for all Fusarium spp., and the activity were significantly lower for F. solani (65.9%) than for non-F. solani species (93.6%). This highlights the need to identify Fusarium spp. when using ophthalmic medications. The MICs of topical antifungal drugs showed no significant increase from 2013 to 2024. These results lay the foundation for multicenter studies of epidemiological cutoff value. Through the prospective observation of clinical efficacy in five patients, the feasibility of treating Fusarium keratitis with topical natamycin combined with chlorhexidine and chlorhexidine alone was also evaluated. Four of the patients achieved clinical cure; the fourth presented with full corneal ulceration, after the opportunity for early drug treatment had passed, and required corneal transplantation. The findings of this study pave the way for multicenter research on the treatment of fungal keratitis with natamycin combined with chlorhexidine.