Investigation of Antibacterial Properties of St. John's wort oil (Hypericum perforatum L.) and Maryam's plant (Geum urbanum L.)

This study aimed to evaluate the in vitro antibacterial activity of St. John’s wort (Hypericum perforatum L.) oil and Geum urbanum L. extracts against standard bacterial strains. Plant materials were collected from mountainous areas of the Karamürsel district in Kocaeli province, Türkiye. St. John’s wort oil was prepared by macerating the plant material in olive oil under dark conditions for six months. Geum urbanum extracts were obtained using different organic solvents, including ethanol, methanol, and chloroform, to assess the effect of solvent type on extraction performance and antibacterial activity. Antibacterial activity was evaluated using the disk diffusion method against Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 15442, and Klebsiella aerogenes ATCC 13048. St. John’s wort oil alone exhibited inhibitory activity against S. aureus (10 ± 0.5 mm) and P. aeruginosa (8 ± 0.6 mm), while no inhibition was observed against K. aerogenes. In contrast, combinations of H. perforatum oil with G. urbanum extracts demonstrated enhanced antibacterial activity against all tested strains. The most pronounced effects were observed with ethanol and methanol extracts. The ethanol combination produced inhibition zones of 15 ± 0.7 mm (S. aureus), 15 ± 0.5 mm (P. aeruginosa), and 13 ± 0.6 mm (K. aerogenes), while methanol extracts yielded 16 ± 0.6 mm, 15 ± 0.4 mm, and 10 ± 0.5 mm, respectively. Chloroform extracts showed comparatively lower antibacterial activity. Standard antibiotics produced higher inhibition zones compared to plant-derived samples, confirming the validity of the assay. Overall, these findings indicate that Hypericum perforatum L. oil and Geum urbanum L. extracts, particularly when obtained using appropriate solvents and applied in combination, possess considerable antibacterial potential and may represent promising natural agents against clinically relevant pathogenic bacteria.