Tigecycline and colistin are few of last-resort defenses used in anti-infection therapies against carbapenem-resistant bacterial pathogens. The successive emergence of plasmid-borne tet(X) tigecycline resistance mechanism and mobile colistin resistance (mcr) determinant, renders them clinically ineffective, posing a risky challenge to global public health. Here, we report that co-carriage of tet(X6) and mcr-1 gives co-resistance to both classes of antibiotics by a single plasmid in E. coli. Genomic analysis suggested that transposal transfer of mcr-1 proceeds into the plasmid pMS8345A, in which a new variant tet(X6) is neighbored with Class I integron. The structure-guided mutagenesis finely revealed the genetic determinants of Tet(X6) in the context of phenotypic tigecycline resistance. The combined evidence in vitro and in vivo demonstrated its enzymatic action of Tet(X6) in the destruction of tigecycline. The presence of Tet(X6) (and/or MCR-1) robustly prevents the accumulation of reactive oxygen species (ROS) induced by tigecycline (and/or colistin). Unlike that mcr-1 exerts fitness cost in E. coli, tet(X6) does not. In the tet(X6)-positive strain that co-harbors mcr-1, tigecycline resistance is independently of colistin resistance caused by MCR-1-mediated lipid A remodeling, and vice versa. Co-production of Tet(X6) and MCR-1 gives no synergistic delayed growth of the recipient E. coli. Similar to that MCR-1 behaves in the infection model of G. mellonella, Tet(X6) renders the treatment of tigecycline ineffective. Therefore, co-transfer of such two AMR genes is of great concern in the context of one health comprising environmental/animal/human sectors, and heightened efforts are required to monitor its dissemination.

中文翻译：

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Tet（X）和MCR-1，一个质粒共同产生的两种抗性酶的串扰的机理研究。

替加环素和粘菌素是针对抗碳青霉烯类细菌病原体的抗感染治疗中使用的最后手段。质粒传播的tet（X）替加环素抗药性机制和可移动大肠粘菌素抗性（mcr）决定子的连续出现使它们在临床上无效，对全球公共卫生构成了风险挑战。在这里，我们报告tet（X6）和mcr-1的共同运输通过大肠杆菌中的单个质粒对两种抗生素都产生了共耐药性。基因组分析表明，mcr-1的转座转移进入质粒pMS8345A，其中新的变体tet（X6）与I类整合子相邻。结构指导的诱变很好地揭示了Tet（X6）在表型tigecycline抗性的背景下的遗传决定因素。体内外的综合证据证明了Tet（X6）在破坏替加环素中的酶促作用。Tet（X6）（和/或MCR-1）的存在有力地阻止了替加环素（和/或大肠菌素）诱导的活性氧（ROS）的积累。与mcr-1在大肠杆菌中产生适应成本不同，tet（X6）不会。在共同携带mcr-1的tet（X6）阳性菌株中，替加环素抗性独立于MCR-1介导的脂质A重塑引起的粘菌素抗性，反之亦然。Tet（X6）和MCR-1的共同生产不会产生受体大肠杆菌的协同延迟生长。Tet（X6）类似于MCR-1在mel.ella菌的感染模型中的表现，使得替加环素的治疗无效。因此，