Phytochemical Profiling and Synergistic Antibacterial Activity of Origanum vulgare L. and Salvia sclarea L. Essential Oils Against Sinusitis Pathogens

Background and Aims: The growing prevalence of antimicrobial resistance among upper respiratory tract pathogens has intensified the search for effective alternative treatments. This study aimed to characterise the phytochemical profiles of Origanum vulgare L. and Salvia sclarea L. essential oils (EOs) and evaluate their individual and combined antibacterial activities against sinusitis pathogens.Methods: Chemical compositions of both EOs were determined using GC/MS and GC/FID analysis. The broth microdilution method was used to evaluate minimum inhibitory concentrations. Potential interactions between the two oils were examined using the checkerboard assay, and the fractional inhibitory concentration indices (FICI) were calculated to classify interactions as synergistic, additive, indifferent, or antagonistic.Results: Carvacrol (61.8%) and linalyl acetate (67.0%) were identified as the major constituents of O. vulgare and S. sclarea EOs, respectively. O. vulgare demonstrated antibacterial activity across all tested pathogens (MIC range: 250 to >2000 μg/mL), whereas S. sclarea showed antibacterial activity with MIC values ranging from >1000 to >2000 μg/mL. Combination testing demonstrated synergistic interactions against Staphylococcus aureus (MRSA) (FICI: 0.50) and Streptococcus pneumoniae (FICI: 0.50), with an indifferent effect against S. aureus, Moraxella catarrhalis, and S. mitis.Conclusion: These findings demonstrate the potential of combining chemically distinct EOs with differing functional group profiles to enhance antibacterial efficacy against selected sinusitis pathogens. The synergistic effects support the development of EO-based phytotherapeutic formulations.