In this study the minimal inhibitory concentration (MICs) of tetracycline (Tet), erythromycin (Ery) and benzalkonium chloride (BC) in absence and in presence of a sub-MIC of juglone (Jug) were determined. In addition, the Ethidium bromide (EtBr) efflux assay was performed to assess the effect of Jug on EtBr cells accumulation. Our results showed a selective antimicrobial activity of Jug against the tested strains. A synergistic effect of Jug, drugs (Tet and Ery) and disinfectant (BC) was noticed with a reduction rate varied from 2 to 16-fold. In addition, the efflux of EtBr was inhibited depending on the Jug concentration. In the presence of Jug, a decrease in loss of EtBr from bacteria was observed. The concentration inducing 50 % of EtBr efflux inhibition after 15 min was about 182 μg ml-1 for S. aureus ATCC 25923, 236 μg ml-1 for S. aureus B193 and 195 μg ml-1 for S. aureus B456. It appears from this study that Jug may be used as a natural source for resistance-modifying activity in same bacteria.
Keywords: Antibacterial activity; Efflux pumps inhibitors; Juglone; Staphylococcus aureus.
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