Deciphering the roles of AcrAB-TolC efflux pump in promoting the transmission of antibiotic resistance.

Plasmid-mediated conjugative transfer drives the global dissemination of antimicrobial resistance, posing a global threat to public health. Besides extruding antibiotics, bacterial multidrug efflux pumps modulate virulence, yet their influence on resistance plasmid spread in antibiotic-free settings remains undefined. Herein, we demonstrate that the AcrAB-TolC efflux pump is critical for the horizontal transfer of model plasmid RP4-7 and diverse clinical resistance plasmids. Single deletions of acrA, acrB or tolC significantly reduce plasmid transfer, and complementation fully restores conjugative frequencies to control levels. Mechanistic investigations reveal that acrB deficiency reduces interbacterial contact, diminishes energy metabolism, and impairs activity of the glutamate decarboxylase, quorum sensing and the conjugative systems. Furthermore, we identify chlorpromazine as a potential AcrB ligand, which blocks plasmid transfer both in vivo and in vitro. Collectively, our findings reveal the role of efflux pumps in plasmid transfer and underscore AcrB as a druggable target to curtail the spread of antibiotic resistance.