Exploiting outer-membrane protein promiscuity to induce transient collateral sensitivity via efflux pump competition

In the fight against antimicrobial resistance, the identification of robust collateral sensitivity (CS) patterns could form the basis of successful sequential and combinatorial antimicrobial therapies. While most of the focus has been devoted to study stable CS due to mutations, CS can be transiently induced in Pseudomonas aeruginosa using dequalinium chloride (DC), which increases the expression of the efflux operon mexCD-oprJ . This leads to transient CS to the aminoglycoside tobramycin, whose molecular mechanism remains unclear. Using a combination of experimental results, mechanistic mathematical models and structural simulations, we show that the inactivation of NfxB by DC not only increases mexCD expression but also reduces the effective amount of the MexXY-OprM aminoglycosides efflux pump. Our data suggest that, under conditions of high MexCD production, this efflux pump can outcompete MexXY for the outer-membrane protein OprM, thereby inducing CS to tobramycin. Bayesian fits accurately reproduce measured mexCD expression and minimal inhibitory concentration (MIC) shifts across DC doses. Model predictions were validated in P. aeruginosa PA14 mutants lacking functional outer-membrane channels. Loss of OprJ preserves DC-induced CS to tobramycin, whereas loss of OprM abolishes it. These results identify competition for OprM as the proximal cause of DC-induced, transient CS and provide a generalizable framework for eliciting CS by perturbing shared components of multidrug efflux systems. This strategy suggests immediate avenues to enhance aminoglycoside efficacy while minimizing selection for stable resistance.