Synergistic Antimicrobial and Antibiofilm Activity Optimization of a Thymus vulgaris-Moringa oleifera-Echinacea purpurea Ternary Ethanolic Extract Blend Against Candida albicans and Streptococcus mutans Using L-Optimal Mixture Design.

Antimicrobial resistance and biofilm-associated oral infections require multi-target therapeutic strategies beyond single-extract herbal testing. Using the L-optimal mixture design approach, we optimized a ternary combination of Thymus vulgaris, Moringa oleifera, and Echinacea purpurea ethanolic extracts against Candida albicans and Streptococcus mutans, then characterized the optimized blend's phytochemistry, antimicrobial and antibiofilm efficacy, time-kill pharmacodynamics, antioxidant capacity, and cytotoxic safety. Through HPLC, apigenin, chlorogenic acid, resorcinol, and ferulic acid were identified as dominant constituents. The optimal blend (Run 14: T. vulgaris 0.331, M. oleifera 0.318, E. purpurea 0.352) achieved a fractional inhibitory concentration index of 0.50 against both organisms, maximum inhibition zones of 3.10 cm (C. albicans) and 4.10 cm (S. mutans), biofilm inhibition of up to 93.2 ± 2.1% for C. albicans and 78.4 ± 2.8% for S. mutans, and confirmed fungicidal and bactericidal activity within 48 and 24 h, respectively. DPPH scavenging ranged from 55.19 to 68.73%, and oral epithelial cells (OEC) viability exceeded 83% at 300 µg/mL. All assays included three independent biological replicates; statistical significance was defined as p < 0.05. These findings identify the T. vulgaris-M. oleifera-E. purpurea blend as a synergistic, multi-target antimicrobial candidate with a favorable preliminary safety profile, supporting further development and evaluation against clinical isolates for oral fungal and bacterial infections.