The research aimed to optimize the ultrasound-assisted extraction of secondary metabolites and the antibacterial activity of the plant species Geranium robertianum. The phytochemical profiles of the optimized extracts, as well as their antibacterial and synergistic activity with an antibiotic and their potential mechanisms of action and cytotoxicity, were examined. Response Surface Methodology was used to optimize extraction conditions. Optimized ethanol and acetone extracts were tested via microdilution, checkerboard, time-kill kinetics, and cell membrane permeability methods. The extracts displayed broad antibacterial activity with minimum inhibitory concentrations ranging from 1.25 to 20 mg ml⁻¹. In addition, the extract synergistically reacted with gentamicin against gentamicin-resistant strains of Escherichia coli and Staphylococcus aureus, enhancing the efficacy of the antibiotic up to 32-fold. The extracts demonstrated strain-dependent bactericidal activity in a 24-h time interval. They increase the permeability of the cell membrane, thus disrupting its normal functioning. The cytotoxic concentration (CC₅₀) on human keratinocytes was 1771.24 ± 5.78 µg ml⁻¹ for ethanol extract, and 958.01 ± 6.14 µg ml⁻¹ for acetone extract. Kaempferol, ellagic acid, quercetin, and rutin were recognized as the main components in both extracts. The findings of this study indicate that the extracts of G. robertianum can be considered as potential natural antibacterial agents in the control of microorganisms.

Bacterial biofilm is a complex community of bacterial cells enclosed in a polymer matrix and attached to a biotic or abiotic substrate. In this living form the bacteria are more resistant to antimicrobial agents than in the form of planktonic cells. Biofilm is a common cause of chronic infections in humans, so due to the growing resistance to antibiotics, alternative methods for controlling infections using medicinal plants have been proposed. In this study, the antibiofilm activity of ethanol and acetone extracts of plants Lamium album, Achillea millefolium and Agrimonia eupatoria against eight clinical isolates of human pathogenic bacteria was examined. Inhibition of biofilm formation was demonstrated using the crystal violet test and the effect on metabolic activity was confirmed by the use of resazurin dye test. Ethanol extract of L. album showed the greatest activity against P. aeruginosa (PA9) at a concentration of 20 mg/ml (> 80% of inhibition), while acetone extract acted at a concentration of 5 mg/ml (≥ 18%) against Klebsiella sp. (K9). At a concentration of 10 mg/ml, the ethanol extract of A. millefolium was effective against E. coli (E16) and P. aeruginosa (PA8) (> 70%), while the acetone extract was effective at 2.5 mg/ml (> 80%) against E. coli (E16). Ethanol and acetone extracts of A. eupatoria were effective at a concentration of 10 mg/ml (> 50%) against E. coli (E16). The antibiofilm activity of the tested plant extracts on certain clinical isolates indicates their great potential in the treatment of infections caused by biofilm-producing bacteria.

The present study investigated the phytochemical composition and antioxidant activity of methanol extracts from leaves, stems, and roots of Tanacetum balsamita collected from two Serbian localities. Total phenolic (TPC), flavonoid (TFC), and proanthocyanidin (TPAC) contents were determined, and antioxidant potential was evaluated using the DPPH radical scavenging assay. Roots contained the highest TPC (75.57 mg GAE g⁻¹), while leaves contained the highest TFC (25.37 mg RUE g⁻¹). TPAC was generally low (< 2.16 mg CChE g⁻¹) in all extracts. DPPH scavenging activity was concentration-dependent, with root extracts reaching up to 94.9% inhibition, followed by stems and leaves. These results indicate variation in bioactive compound content and antioxidant capacity among plant organs and collection sites, confirming T. balsamita as a rich source of natural antioxidants for potential use in foods and dietary supplements.

The aim of this study was to investigate the concentration of phenols, flavonoids and tannins and the antimicrobial activity of methanol, ethyl-acetate and acetone extracts of the species Filipendula ulmaria (L.) Maxim. The antimicrobial activity of the extracts was determined for ten different bacterial species. The total concentration of phenols, flavonoids and tannins in the tested extracts was determined spectrophotometrically. The results show that the amount of tested compounds largely depends on the type of solvent used for extraction from the plant material. The total amount of phenols, flavonoids and tannins was higher in polar solvents compared to the non-polar solvent. The highest concentration of phenols was observed in the flower (74.55 mg GA/g), and the lowest concentration of flavonoids was measured in the root (0.04 mg RU/g). The methanol extract of the flower had the highest, whereas the acetone stem extract exhibited the lowest antioxidant activity. Antimicrobial activity, expressed as a minimum inhibitory concentration, was in the range from 0.312 to 10 mg/ml. The tested Gram-positive bacteria were more sensitive than the Gram-negative bacteria. Based on the obtained results, F. ulmaria was proved to be a rich source of phenols, flavonoids, tannins and antioxidants therefore being a prospective natural antimicrobial agent.

Mentha piperita and Melissa officinalis are both well-known medicinal plants that have applications in traditional medicine. In this research the antibacterial activity of the ethanol extracts of M. piperita and M. officinalis was examined against 14 bacterial strains via the microdilution method. Minimum inhibitory concentrations of ethanol extracts of both plant species ranged from 0.312 to 20 mg/mL. Standard strains of Staphylococcus aureus ATCC 25923 at a concentration of 0.312 mg/mL and Bacillus subtilis ATCC 6633 at a concentration of 1.25 mg/mL showed the highest sensitivity to the ethanol extract of M. piperita. Ethanol extract of M. officinalis showed antibacterial activity on standard strains of S. aureus ATCC 25923 and B. subtilis ATCC 6633 at a concentration of 0.625 mg/mL. In addition to the mentioned standard strains, it showed activity on the isolate from the food Proteus spp. at a concentration of 0.312 mg/mL and isolate from the wound Proteus mirabilis at a concentration of 0.625 mg/mL. Mechanism of action of the ethanol extract of M. officinalis was examined on the permeability of the bacterial cell membrane. The effect of the extract on the increased permeability of the cell membrane was measured based on the release of proteins and the percentage of crystal violet binding. Ethanol extract of M. officinalis has been shown to act at the level of the cell membrane in the following bacterial strains of Pseudomonas aeruginosa, S. aureus and Enterococcus spp.