Synergistic Antibacterial and Molecular Docking Evaluation of Rosmarinus officinalis Extracts against Multidrug-Resistant Salmonella spp

The global rise in antimicrobial resistance (AMR) has significantly undermined the efficacy of commonly used antibiotics, posing a critical challenge to public health, especially in low-resource settings. Among resistant pathogens, multidrug-resistant (MDR) Salmonella species are increasingly associated with severe infections, hospitalization, and mortality. This study investigates the antibacterial activity of Rosmarinus officinalis (rosemary) ethanolic and methanolic extracts against MDR Salmonella spp. and evaluates their synergistic potential with ciprofloxacin, a commonly used antibiotic. A multidimensional approach was employed, including antibiotic sensitivity testing, MIC and MBC determinations, checkerboard assay for synergy assessment, Gas Chromatography–Mass Spectrometry (GC-MS) for phytochemical profiling, and molecular docking for mechanistic insight. Disk diffusion results revealed high resistance to most antibiotics tested, with only partial susceptibility to ciprofloxacin and gentamicin. The methanolic extract demonstrated superior antibacterial activity, with lower MIC and MBC values compared to the ethanolic extract. Checkerboard assays confirmed synergistic interactions between both extracts and ciprofloxacin, with a FICI value of 0.375. GC-MS analysis identified various antimicrobial compounds, including phenolics, fatty acids, esters, and phytosterols. Molecular docking showed that several compounds had high binding affinities for bacterial proteins involved in resistance. These findings highlight the potential of R. officinalis extracts, particularly the methanolic fraction, as promising candidates for combination therapy against MDR Salmonella infections, paving the way for novel phytochemical-antibiotic therapeutics