The Potential of Thymus zygis L. (Thyme) Essential Oil Coating in Preventing Vulvovaginal Candidiasis on Intrauterine Device (IUD) Strings

<b>Background/Objectives:</b> Fungal colonization and biofilm formation on intrauterine device (IUD) strings are known to contribute to recurrent infections and decreased contraceptive efficacy. This study aims to develop a novel approach to prevent <i>Candida</i> reservoir and biofilm formation on IUD strings, thereby lowering the risk of IUD-associated vulvovaginal candidiasis (VVC). <b>Methods:</b> Cervicovaginal samples were collected from human cervix using a sterile cytobrush, avoiding microbial contamination. Cytological examination using the Papanicolaou method was performed to detect the presence of <i>Candida</i>. The antifungal effect of the essential oils (EOs) was determined by broth dilution and disk diffusion methods. Antifungal and biofilm inhibitory effects of <i>Thymus zygis</i> (Tz) EO-coated IUD strings were determined by agar diffusion and crystal violet binding assays, while fungal growth on the coated strings was assessed using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) analysis. <b>Results:</b> Tz EO exhibited significantly lower minimum inhibitory concentration (MIC ≤ 0.06 µL/mL) and minimum fungicidal concentration (MFC = 0.24 µL/mL) values compared to <i>Melaleuca alternifolia</i> (Ma) EO (MIC > 0.24 µL/mL, MFC = 1.95 µL/mL), along with larger zones of inhibition (ZOI) against both <i>Candida albicans</i> (110.0 ± 6.0 mm vs. 91.3 ± 7.0 mm) and <i>Candida glabrata</i> (84.0 ± 13.1 mm vs. 50.0 ± 9.2 mm), indicating a stronger antifungal potential. On IUD strings coated with 4% (40 μL/g) Tz EO in hypromellose ointment, the biofilm formation of both <i>C. albicans</i> and <i>C. glabrata</i> strains was inhibited by 58.9% and 66.7%, respectively, as confirmed by SEM and EDX. <b>Conclusions:</b> Tz EO-coated IUD strings effectively inhibit <i>Candida</i> growth, suggesting a promising natural strategy to reduce recurrent IUD-associated fungal infections. However, before these results can be translated to clinical practice, additional research is needed. Future investigations may encompass an extended number of <i>Candida</i> isolates, stability and release studies of the EO in relation to the formulation, toxicity to vaginal mucosa, epithelial cells and sperm motility, and the effect on vaginal microbiotia.