Abstract

Vulvovaginal candidiasis (VVC) is a common mucosal infection that predominantly affects reproductive-aged women. Although conventional antifungal agents remain the primary treatment option, there is growing interest in developing alternative therapeutic approaches that can enhance antifungal efficacy while potentially reducing treatment burden. Natural products have emerged as valuable sources of bioactive compounds with antifungal potential, offering opportunities for novel combination-based therapies. Ebselen (EB), an organoselenium compound with potent redox-modulating and antifungal properties, and its structurally related analogs represent promising candidates for such strategies. Likewise, black seed oil (BSO), derived from Nigella sativa, and its major active constituent, thymoquinone (TQ), have demonstrated antifungal activity against Candida species, supporting their investigation as natural product-based partners in synergistic antifungal combinations. Commercially prepared BSO and purified TQ were tested across a range of concentrations in a broth microdilution assay in combination with EB and novel organoselenium analogs, including Ebselen Oxide (EB-Ox) and N-octyl-1,2-benzisoselenazol-3(2H)-one (APM C6). Minimum inhibitory concentrations (MICs) for single agents and combinations were determined, and the resulting datasets were analyzed using the web-based Synergy Finder platform. EB, EB-Ox, and APM C6 showed consistent synergy with BSO and TQ against C. albicans (clinical isolate S1), as indicated by positive synergy scores relative to monotherapies.

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