Antibacterial and antioxidant activity of the secondary metabolites from in vitro cultures of the Alice sundew (Drosera aliciae).

The objective of the present study was to evaluate the antioxidant as well as the antibacterial properties of secondary metabolites obtained from Drosera aliciae (Alice sundew) plants grown in vitro and to examine the mechanism of their antimicrobial action. Bactericidal activity of extracts from D. aliciae, as well as pure ramentaceone (naphthoquinone), which is present in this plant, were examined against human pathogenic strains of micro-organisms that are both resistant and susceptible to antibiotics. A chloroform extract proved to be more effective than a methanol preparation against all of the tested strains, except for Pseudomonas aeruginosa isolates. The lowest minimal-bactericidal-concentration value was in the case of Staphylococcus aureus (25-50 mg fresh weight·ml(-1)). The influence of D. aliciae extracts and ramentaceone on the synthesis of DNA, RNA or proteins in cultures of Enterococcus faecalis was estimated by measurement of the incorporation of the radioactively labelled precursors [3H]thymidine, [3H]uridine or [3H]leucine respectively. The methanol extract of D. aliciae, except for a moderate effect on DNA synthesis, had no influence on RNA and protein synthesis. The chloroform preparation caused about a 75% decrease in [3H]uridine incorporation in comparison with the control after 60 min and a significant diminution in DNA and protein synthesis (44 and 30% respectively). Ramentaceone also decreased DNA and RNA synthesis, but less efficiently than did the chloroform extract, and it caused no changes in [3H]leucine incorporation. The methanol extract from D. aliciae proved to be an effective antioxidant in both the DPPH (2,2-diphenyl-10-picrylhydrazyl free radical) and the FRAP (ferric reducing antioxidant power) assay, with the activities exceeding those of well-known antioxidants, namely the flavonoids. The chloroform extract and ramentaceone showed no antioxidative properties.