Medical and Molecular Microbiology Unit, Department of Medicine, Faculty of Science, University of Fribourg, Fribourg, Switzerland.
INSERM European Unit (IAME, France), University of Fribourg, Fribourg, Switzerland.
Antimicrob Agents Chemother. 2019 Aug 23;63(9). doi: 10.1128/AAC.00965-19. Print 2019 Sep.
The plasmid-located gene, encoding a putative phosphoethanolamine transferase, was identified in a colistin-resistant human fecal strain belonging to a very rare phylogroup, the D-ST69-O15:H6 clone. This MCR-9 protein shares 33% to 65% identity with the other plasmid-encoded MCR-type enzymes identified (MCR-1 to -8) that have been found as sources of acquired resistance to polymyxins in Analysis of the lipopolysaccharide of the MCR-9-producing isolate revealed a function similar to that of MCR-1 by adding a phosphoethanolamine group to lipid A and subsequently modifying the structure of the lipopolysaccharide. However, a minor impact on susceptibility to polymyxins was noticed once the gene was cloned and produced in an K-12-derived strain. Nevertheless, we showed here that subinhibitory concentrations of colistin induced the expression of the gene, leading to increased MIC levels. This inducible expression was mediated by a two-component regulatory system encoded by the and genes located downstream of Genetic analysis showed that the gene was carried by an IncHI2 plasmid. analysis revealed that the plasmid-encoded MCR-9 shared significant amino acid identity (ca. 80%) with the chromosomally encoded MCR-like proteins from spp. In particular, was found to harbor a gene encoding MCR-BG, sharing 84% identity with MCR-9. That gene was neither expressed nor inducible in its original host, which was fully susceptible to polymyxins. This work showed that genes may circulate silently and remain undetected unless induced by colistin.
质粒定位的基因，编码一个假定的磷酸乙醇胺转移酶，在属于非常罕见的 phylogroup 的耐粘菌素的人类粪便菌株中被鉴定出来，该菌株属于 D-ST69-O15:H6 克隆。这种 MCR-9 蛋白与其他已发现的质粒编码的 MCR 型酶（MCR-1 至 -8）具有 33%至 65%的同一性，这些酶是多粘菌素获得性耐药的来源。对 MCR-9 产生菌的脂多糖分析表明，通过向脂质 A 添加磷酸乙醇胺基团并随后修饰脂多糖的结构，该 MCR-9 具有与 MCR-1 相似的功能。然而，一旦克隆并在源自 K-12 的菌株中产生 基因，就会注意到对多粘菌素的敏感性略有影响。然而，我们在这里表明，亚抑菌浓度的粘菌素诱导 基因的表达，导致 MIC 水平升高。这种诱导表达是由位于 下游的 和 基因编码的双组分调控系统介导的。遗传分析表明，基因携带在 IncHI2 质粒上。序列分析显示，质粒编码的 MCR-9 与 spp. 染色体编码的 MCR 样蛋白具有显著的氨基酸同一性（约 80%）。特别是，发现 含有编码 MCR-BG 的基因，与 MCR-9 具有 84%的同一性。该基因在其原始宿主中既不表达也不诱导，该宿主对多粘菌素完全敏感。这项工作表明，基因可能沉默地循环，并且除非被粘菌素诱导，否则不会被检测到。
