Eugenol Activity Against Escherichia coli and Staphylococcus aureus: Biofilm Disruption and Additive Interactions with Antibiotics

The emergence of multidrug-resistant bacteria and their ability to form biofilms represent significant challenges in infection control. This study evaluated the antibacterial and antibiofilm activities of eugenol (Eug) against Escherichia coli and Staphylococcus aureus from food and clinical sources. Antibacterial activity was assessed using disk diffusion, broth microdilution (MIC/MBC), and bacterial growth kinetics. Antibiofilm activity was measured by crystal violet staining, CFU enumeration, and scanning electron microscopy (SEM). Checkerboard assays evaluated the combinatorial effect of Eug with ciprofloxacin and oxacillin. Eug exhibited inhibition zones of 13-22 mm and MIC/MBC values of 1000-2000 µg/mL. Subinhibitory concentrations significantly delayed bacterial growth. Biofilm biomass was reduced by up to 90% in E. coli and 80% in S. aureus, with SEM confirming structural alterations. Checkerboard assays revealed additive interactions with antibiotics. These findings provide additional evidence of Eug's antibacterial properties and support further investigation into its combinatorial effects with antibiotics against biofilm-associated challenges.