Benzydamine Reverses TMexCD-TOprJ-Mediated High-Level Tigecycline Resistance in Gram-Negative Bacteria

Recently, a novel efflux pump gene cluster called tmexCD1-toprJ1 and its variants have been identified, which undermine the antibacterial activity of tigecycline, one of the last remaining options effective against multidrug-resistant (MDR) Gram-negative bacteria. Herein, we report the potent synergistic effect of the non-steroidal anti-inflammatory drug benzydamine in combination with tigecycline at sub-inhibitory concentrations against various temxCD-toprJ-positive Gram-negative pathogens. The combination of benzydamine and tigecycline killed all drug-resistant pathogens during 24 h of incubation. In addition, the evolution of tigecycline resistance was significantly suppressed in the presence of benzydamine. Studies on the mechanisms of synergism showed that benzydamine disrupted the bacterial proton motive force and the functionality of this kind of novel plasmid-encoded resistance-nodulation-division efflux pump, thereby promoting the intracellular accumulation of tigecycline. Most importantly, the combination therapy of benzydamine and tigecycline effectively improved the survival of Galleria mellonella larvae compared to tigecycline monotherapy. Our findings provide a promising drug combination therapeutic strategy for combating superbugs carrying the tmexCD-toprJ gene.