A plethora of toxin-antitoxin systems exist in bacteria and has multilateral roles in bacterial pathogenesis and virulence. Toxin-antitoxin systems have been involved in persister cell formation in Escherichia coli and Mycobacterium but have not been reported to be associated with Staphylococcus aureus persistence. Persistence is the ability of bacterial cells to tolerate unfavorable conditions and multiple stresses. There are less known and more unknown factors that either alleviate or aggravate bacterial persistence phenomenon. For the first time, we reported a new chromosomally encoded tripartite toxin-antitoxin system and its role in S. aureus persister cell formation. The toxin gene is bacteriostatic in action and counterbalanced by antitoxin RNA that could basepair with the toxin mRNA and formed a duplex. The transcriptional regulator positively regulates the toxin expression under certain stress conditions. The toxin ectopic induction increased S. aureus susceptibility to norfloxacin, ciprofloxacin, and ofloxacin. Whole-genome RNA sequencing revealed that MDR efflux pump norA is significantly down-regulated by toxin ectopic induction. The deletion of norA from S. aureus genome reduced resistance toward ciprofloxacin, norfloxacin, and ofloxacin, as well as resulted in a decrease in minimal inhibitory concentration while complementation of norA successfully restored the phenotypes. The persistence assay of the norA mutant revealed that deletion of norA increased persister cell survival in S. aureus. Altogether, we have provided insight into the first tripartite type-I TA system and revealed the role of MDR NorA in the persister cell formation of S. aureus.

细菌中存在大量的毒素-抗毒素系统，并且在细菌的发病机理和毒力中具有多方面的作用。毒素-抗毒素系统已参与大肠杆菌和分枝杆菌的持久性细胞形成，但尚未报道与金黄色葡萄球菌的持久性有关。持久性是细菌细胞耐受不利条件和多重压力的能力。缓解或加剧细菌持久性现象的因素鲜为人知，未知数更多。我们首次报告了一种新的染色体编码的三方毒素-抗毒素系统及其在金黄色葡萄球菌中的作用持续性细胞形成。毒素基因具有抑菌作用，并被可以与毒素mRNA碱基配对并形成双链体的抗毒素RNA抵消。在某些压力条件下，转录调节因子可积极调节毒素的表达。毒素异位诱导增加了金黄色葡萄球菌对诺氟沙星，环丙沙星和氧氟沙星的敏感性。全基因组RNA测序表明，毒素异位诱导显着下调了MDR外排泵norA。的缺失诺拉从金黄色葡萄球菌基因组减少朝向环丙沙星电阻，诺氟沙星，氧氟沙星和，以及导致了最小抑制浓度的降低而互补NORA成功恢复了表型。对norA突变体的持久性测定显示，norA的缺失增加了金黄色葡萄球菌的持久性细胞存活率。总之，我们提供了对第一个I型三方I TA系统的见解，并揭示了MDR NorA在金黄色葡萄球菌的持久性细胞形成中的作用。