Targeting Oral Pathogens with Salvia officinalis and Nigella sativa Supercritical CO(2) Extracts: A Pharmacodynamic Approach and Three-Dimensional Checkerboard Synergy for Novel Dental Antimicrobials.

Background: Oral infections such as dental caries and candidiasis are mediated by resilient biofilms, which are increasingly tolerant to conventional antimicrobials. This study investigated the antimicrobial and antibiofilm effects of Salvia officinalis and Nigella sativa CO(2) extracts against Streptococcus mutans and Candida albicans, with emphasis on synergistic interactions. Methods: Extracts were analyzed using gas chromatography-mass spectrometry analysis (GC-MS) and evaluated through planktonic MIC/MBC assays, time-kill kinetics, and biofilm models (MBIC/MBEC, biomass, metabolic activity). A novel three-dimensional checkerboard (3D-CB) and fractional inhibitory concentration index (FICI) approach was applied to optimize extract ratios, concentrations, and exposure times. Results: S. officinalis extract showed greater activity against S. mutans (MIC 256 mg/L; MBC 512 mg/L), while N. sativa was more effective against C. albicans (MIC 256 mg/L; MFC 512 mg/L). Both extracts reduced biofilm biomass and metabolic activity by over 70% at higher doses. Synergy was confirmed at ratios of 70:30 (S. officinalis: N. sativa) for S. mutans (FICI 0.38) and 40:60 for C. albicans (FICI 0.42). The achieved synergistic effect further decreased MBEC values fourfold and prolonged post-antibiotic effects. Conclusions: Synergistic S. officinalis-N. sativa formulations enhanced antimicrobial activity against oral pathogens in both planktonic and biofilm states, supporting their potential as next-generation dental antimicrobials.