Antibacterial activity of hydroethanolic leaf extracts of Allium ursinum before and after flowering against selected foodassociated bacteria

Abstract

Ramsons (Allium ursinum L.; wild garlic) is a seasonal edible Allium species traditionally consumed for health-promoting properties. Here we investigated whether the antibacterial activity of crude leaf extracts depends on the phenological stage of the plant. Fresh leaves collected before and after flowering were extracted with ethanol:water (30:70, v/v), concentrated, re-dissolved in 30% ethanol, sterile-filtered, and tested against a panel of food-associated bacteria and pathogens by broth microdilution. Minimum inhibitory concentrations (MIC) were defined by absorbance-based growth inhibition, and minimum bactericidal concentrations (MBC) were determined by viability plating (track plate method). The pre-flowering extract showed no clear inhibitory activity within the tested concentration range (MIC >20 mg/mL for all strains). In contrast, the post-flowering extract displayed measurable antibacterial activity, most notably against Escherichia coli (MIC >10.8 mg/mL; MBC 10.8 mg/mL) and Staphylococcus aureus (MIC 21.5 mg/mL). Several strains exhibited bactericidal endpoints only at the highest tested concentration, while Serratia marcescens remained poorly susceptible based on MIC values. In addition, Bacillus cereus var. mycoides showed an unusual concentration-dependent response with growth stimulation at subinhibitory concentrations. Our findings indicate that the antibacterial potential of crude A. ursinum leaf extracts is stage-dependent and highlight the need for chemical characterization and standardized preparation to support food- or health-related applications.