The effect of extracts of grapefruit seeds (EGSs), sea-buckthorn leaves (EBLs), and chaga (ECs) on model lipid membranes has been investigated. It has been shown that the threshold concentrations of EGSs and ECs that induced destabilization of phosphatidylglycerol-enriched bilayers are 1.3–1.4 times lower than for phosphatidylcholine-containing membranes. It has been established that EGSs and EBLs reduce the boundary potential of membranes formed from a mixture of phosphatadylcholine and cholesterol (the changes reach 45 and 40 mV at concentrations of 60 and 800 μg/mL, respectively). ECs did not produce pronounced potential-modifying effect. It was shown that changes in the boundary potential in the presence of EBLs were due to the presence of flavonols, quercetin, and myricetin in its composition. Using the method of differential scanning calorimetry, it was also found that quercetin and myricetin were able to influence the thermotropic behavior of membrane lipids and, consequently, their packing density. The potentiation of the pore-forming activity of the antifungal polyene macrolide nystatin and antibacterial lipopeptide polymyxin B was shown with introduction of an EBLs. These data indicate a possible synergism of the antimicrobial action of the tested antibiotics and EBLs, which can be used to generate combined broad-spectrum antimicrobial agents.
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