Integrative Clinical and In-vitro Evaluation of Antifungal Resistance, Biofilm Formation, and Synergistic Activity of Ocimum gratissimum Essential Oil Against Clinical Candida Isolates in Vietnam

Antifungal resistance in Candida species presents a growing clinical challenge, particularly in Southeast Asia where regional epidemiology remains underexplored. This study retrospectively analyzed 423 clinical Candida isolates collected in Vietnam between 2017 and 2018, integrating clinical epidemiology with in-vitro biofilm inhibition and synergy assays. Non-albicans Candida species predominated, with C. tropicalis accounting for 25.8% of isolates. Fluconazole resistance was detected in 13.7% of isolates, markedly higher than rates typically reported in Western populations (4–8%). Biofilm formation capacity was substantial, and biofilm biomass positively correlated with fluconazole MICs (Spearman’s ρ = 0.873, p < 0.001). Ocimum gratissimum essential oil (OGEO) demonstrated potent biofilm inhibition, achieving a mean 89.6% reduction at 2% concentration. Checkerboard synergy assays revealed synergistic activity (FICI ≤ 0.5) between OGEO and clotrimazole in 65% of tested isolates. These findings highlight OGEO as a promising phytotherapeutic adjuvant capable of enhancing azole efficacy and mitigating resistance development. This integrative analysis provides novel region-specific insights supporting the inclusion of biofilm-targeted strategies within antifungal stewardship programs in resource-limited settings.