Phytochemical Characterization and Anti-Biofilm Activity of Primula veris L. Roots

In this study, three new undescribed triterpene saponins named primulasaponin III-V (19-21) were isolated from the roots of Primula veris L. of Bulgarian origin together with the known primulasaponin I. Their structures were elucidated via 1D and 2D NMR spectroscopy and HR-ESI-MS. In addition, 17 known phenolic compounds (six flavones, three acetophenones, four bisbibenzyls, and four phenolic glycosides) were identified in the chloroform and methanol extracts. Among them, flavone, 2'-methoxyflavone, 3'-methoxyflavone, 3'-hydroxy-4',5'-dimethoxyflavone, 2',5'-dimethoxyflavone, 3'-methoxy-4',5'-methylendioxyflavone, paeonol, 2-primeverosyl-5-methoxy-acetophenone, and paeonolide were detected for the first time in the roots of P. veris. The minimum inhibitory and minimum bactericidal concentrations of the chloroform and methanol extracts of P. veris roots and the saponin-enriched fraction were determined, with MIC values ranging between 0.5 and 1 mg/mL. Additionally, the tested samples were evaluated for their ability to inhibit biofilm formation in the presence of sub-MICs. All tested samples showed better biofilm inhibition of Gram-negative strains compared to Gram-positive strains. The strongest effect was observed for the chloroform extract against the biofilm formation of Pseudomonas aeruginosa, while the saponin-enriched fraction showed the highest percentage of biofilm inhibition of Escherichia coli, Staphylococcus aureus, and Staphylococcus mutans. At the same time, chloroform extract showed lower cytotoxicity against human keranocyte cell line HaCaT, as compared with methanol extract and the saponin-enriched fraction.