LAUSR

AIMS The research aimed to optimize the ultrasound-assisted extraction of secondary metabolites and 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, their potential mechanisms of action and cytotoxicity, were examined. METHODS AND RESULTS Response Surface Methodology was used to optimize extraction conditions. Optimized ethanol and acetone extract 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 E. coli and S. aureus enhancing the efficacy of the antibiotic up to 32-fold. The extracts demonstrated strain-dependent bactericidal activity in a 24-hour 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. CONCLUSIONS 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.