Integrated experimental and computational study reveals enhanced antimicrobial efficacy of amoxicillin loaded in oleic acid nanoemulsion against multidrug-resistant <i>Salmonella typhimurium</i>

The escalating crisis of antimicrobial resistance (AMR) poses a severe threat to global health, demanding innovative strategies to rejuvenate conventional antibiotics against multidrug-resistant (MDR) pathogens like <i>Salmonella typhimurium</i>. This study presents an integrated experimental and computational investigation into an oleic acid-based nano-emulsion designed to restore amoxicillin's potency. The amoxicillin-loaded nano-emulsion, prepared <i>via</i> spontaneous emulsification and ultrasonication, yielded stable, semi-spherical nanoparticles with a mean hydrodynamic diameter of 199.6 nm, a low polydispersity index (0.331), and a high negative zeta potential of -46.3 mV, ensuring excellent colloidal stability. <i>In vitro</i> antimicrobial testing against MDR <i>S. Typhimurium</i> revealed a profound 2.3-fold enhancement in antibacterial activity; the nano-formulation produced an inhibition zone 133% larger (35.0 ± 2.1 mm) than free amoxicillin (15.0 ± 1.8 mm). To elucidate the molecular underpinnings, molecular docking and 100 ns molecular dynamics simulations confirmed the stable, high-affinity binding of amoxicillin within the catalytic cleft of its target enzyme, Penicillin-Binding Protein 3 (PBP3a). The interaction, with a strong binding affinity of -9.4 kcal mol^-1, was energetically driven by dominant van der Waals (-27.1 kcal mol^-1) and electrostatic (-80.6 kcal mol^-1) forces, yielding a total binding free energy of -32.0 ± 8.0 kcal mol^-1 <i>via</i> MM-PBSA analysis. Crucially, <i>in silico</i> ADMET predictions forecast a paradigm shift in pharmacokinetics, projecting a 132 000-fold increase in intestinal absorption and a 95-fold reduction in hepatotoxicity risk. These integrated findings provide a robust, mechanistically detailed rationale for using oleic acid nano-emulsions as a powerful delivery platform to overcome bacterial resistance.