Drug efflux systems have recently been recognized as a significant mechanism responsible for multidrug resistance in bacteria. In this study, we described the identification and characterization of a new chromosomally encoded efflux pump (SA00565) in Staphylococcus aureus. SA00565, which belongs to the drug/metabolite transporter (DMT) superfamily, was predicted to be a 10-transmembrane segment transporter. To evaluate the role of sa00565 in resistance, we generated sa00565 gene deletion mutant (Δsa00565) and assessed its susceptibility to 35 different antibiotic treatments. Our results demonstrated that the Δsa00565 mutant exhibited reduced resistance to tetracycline and doxycycline, with 64-fold and 12-fold decreased MICs, respectively. The mechanism of SA00565-mediated tetracycline resistance was demonstrated that SA00565 possesses the capability to efficiently extrud intracellular tetracycline into the environment. The efflux activity of SA00565 was further validated using EtBr accumulation and efflux assays. In summary, our study uncovered a previously unknown function of a DMT family transporter, which serves as a tetracycline efflux pump, thereby contributing to tetracycline resistance in S. aureus.IMPORTANCEIn this study, we addressed the significance of drug efflux systems in multidrug resistance of Staphylococcus aureus, focusing on the unexplored efflux pump SA00565 in the drug/metabolite transporter (DMT) superfamily. Through phylogenetic analysis, gene knockout, and overexpression experiments, we identified the role of SA00565 in antibiotic resistance. The Δsa00565 mutant showed increased susceptibility to tetracycline and doxycycline in disk diffusion assays, with significantly lower MICs compared to the WT. Remarkably, intracellular tetracycline concentration in the mutant was two- to threefold higher, indicating SA00565 actively eliminates intracellular tetracycline. Our findings emphasize the pivotal contribution of SA00565 to tetracycline antibiotic resistance in S. aureus, shedding light on its functional attributes within the DMT superfamily and providing valuable insights for combating multidrug resistance.
Keywords: DMT transporters; S. aureus; antibiotic resistance; drug efflux pump; tetracycline resistance.