In Vitro Antibacterial Effects of Haskap Berry (Lonicera caerulea L.) Ethanol Extract against Diarrheagenic...

Diarrheagenic Escherichia coli (DEC) poses a significant threat to public health due to its potential to induce severe gastrointestinal illnesses and fatalities. This study was conducted to evaluate the in vitro antibacterial properties and mechanisms of action of ethanol extract derived from haskap berries (Lonicera caerulea L.) (LCEE) against 7 important serotypes among DEC. Chemical analysis unveiled the substantial presence of phenols, flavonoids, and anthocyanins in LCEE, with cyanidin emerging as the predominant anthocyanidin. Antioxidant assays confirmed the potent antioxidant capabilities of LCEE. The DEC treated with LCEE led to conspicuous inhibition zones, reduced growth rates, and demonstrated notable efficacy, with low minimum inhibitory concentration and minimum bactericidal concentration values against DEC. LCEE exerted strong antimicrobial abilities on DEC by reducing bacterial motility, disrupting biofilm and pre-formed biofilm. LCEE was observed to induce alterations in cell morphology and internal structure, enhance membrane permeability, and induce cellular dysfunction, including cell membrane hyperpolarization and decreased intracellular ATP concentration. SDS-PAGE analysis demonstrated LCEE interfered with protein synthesis, while quantitative real-time PCR (RT-qPCR) assays revealed that LCEE inhibited biofilm formation possibly by reducing the expression levels of genes (including luxS, fliC, csgA, and fimA) associated with biofilm-formation. Cytotoxicity assessments indicated that LCEE exhibited no cytotoxic effects in vitro. These findings highlight the potential of LCEE as a natural antimicrobial agent for mitigating DEC contamination in food, thereby lowering the risk of DEC infections.