Antibacterial and Antibiofilm Activity of a Chemically Characterized Cinnamomum verum Bark Methanolic Extract Against Multidrug‐Resistant Bacteria: Preliminary Antibiotic–Interaction Screening and Exploratory Molecular Docking

Abstract

This study characterized the phytochemical composition of a methanolic bark extract of Cinnamomum verum and evaluated its antibacterial, bactericidal, biofilm-biomass-reducing, and preliminary antibiotic-potentiating effects against reference and multidrug-resistant bacterial strains. The extract was characterized by HPLC-MS; MIC and MBC values were determined by broth microdilution; biofilm biomass was assessed using the crystal-violet assay; and antibiotic-extract interactions were screened by disk diffusion. Molecular docking was used as a hypothesis-generating approach to investigate interactions between identified phytochemicals and GyrB, LasA, and PBP1a. Seventeen compounds were identified, with trans-cinnamaldehyde as the predominant quantified constituent, followed by quinic acid, rutin, and protocatechuic acid. The extract inhibited all tested bacteria, with MIC and MBC values of 0.625-5 and 2.5-20 mg/mL, respectively, and MBC/MIC ratios consistent with bactericidal activity. Imipenem-resistant Acinetobacter baumannii isolates were the most susceptible. The extract also reduced biofilm biomass in a concentration-dependent and strain-dependent manner. Disk-diffusion screening identified antibiotic- and isolate-dependent increases in inhibition zones, particularly for cefoxitin and fosfomycin against MRSA and for selected combinations against A. baumannii; however, some combinations were unchanged or produced smaller zones, and pharmacological synergy was not established. Docking prioritized quercetin, 1,3-di-O-caffeoylquinic acid, and quercetin-3-O-rhamnoside as candidates for subsequent target-based validation.