Antimicrobial, antibiofilm and potential efflux-modulating activities of Allium cepa (pink variety) against selected bacterial and mycobacterial pathogens

Antimicrobial resistance and biofilm formation contribute to persistent bacterial infections. This study evaluated the antimicrobial, biofilm-inhibitory and potential efflux-modulating activities of hydroethanolic crude extract and solvent fractions of the pink variety of Allium cepa against selected bacterial and mycobacterial pathogens. The ethyl acetate fraction showed the greatest antimicrobial activity, with minimum inhibitory concentrations (MICs) of 8–250 µg/mL, including 8 µg/mL against Mycobacterium aurum and 62.5 µg/mL against M. smegmatis . At three concentrations below their respective MICs, the preparations produced concentration-dependent reductions in crystal-violet-stained biofilm-associated biomass. At ½ MIC, they also increased intracellular ethidium bromide-associated fluorescence relative to untreated controls, consistent with altered EtBr accumulation and potential modulation of bacterial efflux or related transport processes. HPLC profiling showed distinct chromatographic profiles and relative peak-area distributions between the crude extract and ethyl acetate fraction. These findings demonstrate antimicrobial and biofilm-inhibitory activities and support further investigation of the potential resistance-modifying properties of A. cepa .