Essential oils (EOs), as eco-friendly bioactive compounds, offer a sustainable strategy to enhance food safety and curb antibiotic administration in livestock production. In this study, six food-grade EOs, Thymbra capitata, Thymus vulgaris, Eugenia caryophyllata, Coridothymus capitatus, Thymus capitatus, and Thymus serpyllum, were evaluated for their synergistic potential with tetracycline (Tc) against multidrug-resistant Salmonella enterica strains isolated from the swine production chain. Checkerboard assays showed that EOs were able to restore Tc susceptibility in resistant S. enterica strains, reducing minimum inhibitory concentrations from 256 to ≤4 µg/mL, bringing the values within the Clinical and Laboratory Standards Institute breakpoints (2020). The strongest synergistic effects were observed for carvacrol-rich EOs, with Fractional Inhibitory Concentration Index values below 1, probably due to the key role of the EO phytocomplex, such as terpenoid components that modulate antibiotic efficacy (as observed through Principal Component Analysis). The combination of EOs and antibiotics represents a promising strategy to overcome antimicrobial resistance in the food supply chain. This approach aligns with the One Health perspective by promoting animal health, improving food safety, and reducing environmental impact through decreased antibiotic pressure. These findings support the integration of plant-based antimicrobials into livestock management practices as part of a sustainable and holistic strategy to limit antimicrobial resistance, contributing to more responsible and resilient food systems.

- CLSI guidelines (2020). Performance Standards for Antimicrobial Susceptibility Testing, 30th ed. CLSI 447 supplement M100S.