| Summary: | The bulbs of <i>Allium</i> species are a known source of antibacterial phytochemicals. Anti-infective, efflux pump and biofilm inhibitory activities of bulb extracts of selected Ghanaian shallots <i>Allium cepa</i> var aggregatum were evaluated using the HT-SPOTi assay and other whole-cell phenotypic screening techniques to determine their possible mechanisms of action. Ethanol and aqueous extracts of white <i>A. cepa</i> inhibited the growth of <i>Mycobacterium smegmatis</i> mc<sup>2</sup> 155 and <i>Escherichia coli,</i> respectively. The majority of the <i>Allium</i> extracts significantly (<i>p</i> < 0.05) exhibited efflux pump inhibitory activity against all the acid-fast, Gram-positive and Gram-negative strains used. Hexane and chloroform extract of the pink <i>A. cepa</i> and the aqueous extract of the white <i>A. cepa</i> significantly inhibited <i>M. smegmatis</i> biofilm formation. For <i>Pseudomonas aeruginosa</i>, the inhibition was observed at 250 µg/mL for the aqueous extract (~77.34%) and 125 µg/mL for the hexane extract (~76.51%). The results suggest that Ghanaian shallots could potentially be useful when further developed to tackle antimicrobial resistance, particularly in tuberculosis (TB).
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