Active components and mechanisms of Glycyrrhiza uralensis Fisch. in treating methicillin-resistant Staphylococcus epidermidis infections

Abstract:

Objective To identify the active components in Glycyrrhiza uralensis Fisch. that inhibit methicillin-resistant Staphylococcus epidermidis (MRSE) infections and explore their potential antibacterial mechanisms.Methods The half-dilution method was employed to assess the inhibitory activities of pharmacological components from G. uralensis against MRSE. The anti-MRSE phenotype of this medicinal herb was evaluated by microbial adhesion to hydrocarbons, crystal violet staining, scanning electron microscopy, and integrated cell imaging. Additionally, metabolomic analysis was conducted via gas chromatography-mass spectrometry (GC-MS), and the activity of intracellular oxidative dehydrogenase was measured by a commercially available reagent kit. The propidium iodide and laurdan dyes were utilized to assess the membrane damage and fluidity of cells. The challenge test was conducted with the larvae of Galleria mellonella to determine the antibacterial activities of tested pharmacological components in vivo.Results Licochalcone A, licochalcone C, and glabridin from G. uralensis demonstrated significantly inhibitory activities against MRSE. Among these compounds, licochalcone A exhibited the strongest inhibitory effect on MRSE, with a minimum inhibitory concentration (MIC) of 6.0 μg/mL and a minimum bactericidal concentration (MBC) of 12.0 μg/mL. The metabolomic analysis indicated that licochalcone A primarily influenced the metabolic pathways, secondary metabolite biosynthesis, and ATP-binding cassette (ABC) transport systems of MRSE. This compound impeded the biosynthesis of ornithine, lysine, and niacin, leading to the accumulation of 1,3-dipalmitin in the cells. Phenotypic experiments corroborated that licochalcone A downregulated the tricarboxylic acid (TCA) cycle flux and reduced the intracellular ATP level in MRSE. Furthermore, it inhibited the biofilm formation and intracellular protein expression, thereby preventing MRSE from adhering to HaCaT cells. Additionally, licochalcone A disrupted the structural integrity of the MRSE cell membrane, resulting in cell collapse, deformation, and even rupture and increased the survival rate of G. mellonella larvae following MRSE infection.Conclusion Exposure to licochalcone A alters the metabolism of sugars, lipids, and amino acids in MRSE cells, thereby influencing the biofilm formation, biosynthesis of secondary metabolites such as proteins, and the remodeling of cell membranes. Consequently, this alteration results in an antimicrobial phenotype characterized by decreased ATP production, impaired transporter function, and reduced adhesion and infection of MRSE.

Key words:Glycyrrhiza uralensis Fisch.;licochalcone A;methicillin-resistant Staphylococcus epidermidis;metabolomics;metabolic pathway;ABC transport