Background and Purpose: Candidiasis is a common fungal infection, with increasing cases caused by resistant non-albicans species, such as
Candida krusei and
Candida glabrata. These species present remarkable clinical treatment challenges due to their resistance, particularly with azole antifungals, like fluconazole (FLZ). This study aimed to evaluate the antifungal potential of thyme (Thymus vulgaris) essential oil nanoemulsion (TEONE) against these resistant
Candida strains, focusing on its impact on resistance gene expression and the enhancement of conventional treatment efficacy. Materials and Methods: TEONE was formulated by combining thyme EO with Tween ۸۰ and water using the antisolvent precipitation method to create a stable nanoemulsion. The TEON was characterized by using Scanning Electron Microscopy for morphology, dynamic light scattering for particle size, and zeta potential for stability and surface charge assessment. The antifungal activity of TEONE,
Thyme EO, and FLZ was assessed against
Candida strains using disk diffusion, microdilution, and checkerboard assays. The quantitative reverse transcription polymerase chain reaction was employed to evaluate the expression of resistance genes (ABC۱, CDR۱, and ERG۱۱) following treatment. Results: The Scanning Electron Microscopy revealed a predominantly spherical morphology with minimal rod-shaped particles, while Dynamic Light Scattering confirmed a mean droplet size of ۱۳۴.۳ nm and a polydispersity index of ۰.۴۰۲, indicating good dispersion. Zeta potential analysis showed a value of -۷۸.۶ mV, suggesting strong stability of nanoemulsion. The TEONE demonstrated significant antifungal activity, reducing minimum inhibitory concentration values by up to ۵۰%, compared to
Thyme EO (p<۰.۰۵). Disk diffusion tests showed larger inhibition zones for TEONE (۲۰-۲۵ mm), compared to
Thyme EO (۱۵-۱۸ mm) (p<۰.۰۱). The quantitative reverse transcription polymerase chain reaction revealed that TEONE reduced CgCDR۱ expression by up to ۴۹% in
Candida glabrata and downregulated ERG۱۱ and ABC۱ in
Candida krusei (p<۰.۰۵). Conclusion: While FLZ alone tended to increase resistance gene expression, combining TEONE with FLZ mitigated this effect and enhanced antifungal efficacy, indicating an additive interaction. TEONE represents a promising natural approach for enhancing antifungal treatment strategies against resistant
Candida infections, offering potential benefits as an alternative or complementary therapy to conventional antifungal agents. These nanoemulsions may also allow for a reduction in the dosage of traditional drugs such as FLZ, potentially minimizing side effects and the development of resistance.
