Restoring tigecycline efficacy with lysine supplementation in tmexCD-toprJ-positive bacteria

Antimicrobial resistance is one of the most pressing challenges to global public health. Tigecycline, a last-resort antibiotic, has been undermined by the emergence of the tmexCD1-toprJ1 gene cluster, a transferable RND-type efflux pump that confers resistance. Metabolite-enabled killing of antibiotic-resistant pathogens by antibiotics is an attractive strategy to tackle antibiotic resistance.

The potentiation of lysine to tigecycline was evaluated through a series of in vitro studies, including bacterial viability assays, time-kill kinetics analysis, persister assays, and biofilm eradication experiments, as well as in vivo assessment using a murine systemic infection model. The underlying mechanisms of action were further explored through transcriptomic profiling and biochemical validation.

Herein, we show that lysine synergistically enhances the antibacterial efficacy of tigecycline against tmexCD-toprJ-positive bacteria. Mechanistic studies indicate that lysine supplementation promotes tigecycline uptake by upregulating ∆pH and disrupting membrane permeability. Transcriptomic analysis, coupled with phenotypic experiments, indicates that lysine not only triggers the generation of reactive oxygen species (ROS) by inhibiting hydrogen sulfide (H₂S) production but also downregulates energy metabolism pathways essential for efflux pump function. These effects promote intracellular accumulation of tigecycline, thereby overcoming tmexCD-toprJ-mediated resistance. In mouse infection models, the combination of lysine and tigecycline shows improved therapeutic efficacy compared to tigecycline monotherapy.

Collectively, our findings indicate that lysine can serve as a promising tigecycline booster to tackle infections caused by tmexCD-toprJ-positive bacteria.