Disruption of metabolic function and redox homeostasis as antibacterial mechanism of Lindera glauca fruit essential oil against Shigella flexneri

Current trend in food safety and public health is focusing on the use of natural antimicrobials. The Lindera glauca fruit with rich resource and essential oil has emerged as potential application in China. This work aimed to detect chemical compounds of L. glauca fruit essential oil (LGFEO) and to evaluate antimicrobial activity and mechanism of LGFEO for develop natural antimicrobials. A total of 70 volatile compounds were identified, and the major groups were monoterpene (56.62%) and sesquiterpene (39.71%). The analysis of antimicrobial activity indicated that LGFEO could effectively inhibit the growth of all tested 13 food-borne pathogens, of which Shigella flexneri had the highest inhibition zone diameter (DIZ, 25.45 nm), and the lowest minimum inhibitory concentration (MIC, 0.156 μg/mL) and bactericidal concentration (MBC, 0.312 μg/mL). To unravel antibacterial mechanism of LGFEO on S. flexneri, the dynamic changes for bacterial growth curve, material release, and the levels of intracellular mallondialdehyde (MDA), hydrogen peroxide (H2O2), and ROS-detoxifying enzymes were analyzed in S. flexneri cells exposed to LGFEO at different concentrations (1/2 × MIC, 1 × MIC and 2 × MIC) and times (0–24 h), revealing that LGFEO could cause cell material leakage, antioxidant enzyme inactivation, H2O2 and MDA accumulation, and bacterial growth inhibition. Also, antibacterial action of LGFEO was conducted on key enzymes of respiratory metabolic (glycolysis, oxidative pentose phosphate pathway, tricarboxylic acid cycle, and respiratory chain), and the levels of intracellular ATP, ADP, nicotinamide adenine dinucleotide (NAD+ and NADH), nicotinamide adenine dinucleotide phosphate (NADP+ and NADPH), and oxidized and reduced glutathione (GSSG and GSH) in LGFEO-treated S. flexneri cells, indicating a role of LGFEO in repressing respiratory pathway and electron transport with low redox potential. All these revealed that LGFEO could effectively induce H2O2 accumulation and lipid peroxidation, resulting in cell membrane damage and metabolic function disruption, giving rise to a disturbance of redox homeostasis, which may be the main cause of growth inhibition or cell death for S. flexneri.