Antibacterial Activity and Mechanism of Action of Motuo Citron Essential Oil on Staphylococcus aureus and Escherichia coli

This study investigated the antibacterial activity and underlying mechanisms of essential oil extracted from Motuo citron against representative foodborne pathogens, including Staphylococcus aureus and Escherichia coli. The essential oil was obtained by steam distillation, and its chemical composition was analyzed by GC–MS. Limonene, γ-terpinene, and 3-carene were the predominant monoterpenes and may contribute substantially to the antibacterial activity. The Oxford cup assay confirmed strain-specific antibacterial effects. The essential oil showed stronger activity against S. aureus, with an inhibition zone of 22.29 ± 0.82 mm, a minimum inhibitory concentration (MIC) of 3.75 μL/mL, and a minimum bactericidal concentration (MBC) of 7.5 μL/mL. In contrast, its activity against E. coli was weaker, with an inhibition zone of 11.85 ± 0.49 mm, an MIC of 7.5 μL/mL, and an MBC of 15 μL/mL. Mechanistic analyses showed that the essential oil significantly reduced bacterial ATP levels and inhibited key enzymes involved in glycolysis and the tricarboxylic acid cycle, thereby impairing energy metabolism. It also disrupted bacterial cell wall and membrane integrity, resulting in cell rupture and cytoplasmic leakage. In addition, the essential oil disturbed core metabolic pathways, including amino acid biosynthesis, lysine biosynthesis, and tryptophan metabolism, causing severe metabolic imbalance in a dose-dependent manner. Motuo citron essential oil exerts antibacterial effects through the combined disruption of cell membranes, inhibition of energy metabolism, and interference with amino acid metabolism. As a natural plant-derived antibacterial agent, it shows potential for development as a food preservative and pharmaceutical antimicrobial.