State Key Laboratory for Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou University, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, P.R. China.
FASEB J. 2023 May;37(5):e22928. doi: 10.1096/fj.202300215R.
Colistin (polymyxin E) is a group of cationic antimicrobial cyclic peptides and is recognized as a last-resort defense against lethal infections with carbapenem-resistant pathogens. In addition to the plasmid-borne mobilized phosphoethanolamine (PEA) transferases, the functional expression of lipid A-modifying enzymes encoded on chromosomes has been attributed to intrinsic bacterial colistin resistance. However, the mechanisms of colistin resistance in Riemerella anatipestifer remain unknown. Herein, the GE296_RS09715 gene-encoded Lipid A PEA transferases (RaEptA) was identified in R. anatipestifer. Genetic and structural analyses revealed that the amino acid sequence of RaEptA shared 26.6%-33.1% similarities with the family of Lipid A PEA transferases (EptA) and MCR-like proteins and have defined 12 residues that contribute to the formation of phosphatidylethanolamine (PE)-recognizable cavities. Comparative analyses of colistin resistance in RA-LZ01 and RA-LZ01ΔRaEptA showed the level of colistin has fallen from 96 μg mL down to 24 ~ 32 μg mL . Site-directed mutagenesis assay of the PE-binding cavity and expression of the mutants reveals that K309-rRaEptA can remodel the surface of Escherichia coli and rendering it resistant to colistin, suggesting this point-mutation of P309K is necessary for EptA-mediated lipid A modification. Moreover, the virulence of RA-LZ01ΔRaEptA was attenuated compared with RA-LZ01 both in vivo and vitro. Taken together, the results represent the RaEptA involved in the colistin resistance and pathogenicity, and the P309K mutation might alter bacterial adaptation and increase the spread of colistin resistance from R. anatipestifer to other gram-negative bacteria. The findings of this study suggest another scenario for the spread of colistin resistance genes and should be considered by a wide audience.
黏菌素（多黏菌素 E）是一组阳离子型抗菌环肽，被认为是对抗碳青霉烯类耐药病原体致死性感染的最后一道防线。除了质粒携带的可移动磷酸乙醇胺（PEA）转移酶外，染色体上编码的脂 A 修饰酶的功能表达也归因于细菌内在的黏菌素耐药性。然而，鸭疫里默氏杆菌的黏菌素耐药机制尚不清楚。本研究在鸭疫里默氏杆菌中鉴定出了 GE296_RS09715 基因编码的脂 A PEA 转移酶（RaEptA）。遗传和结构分析表明，RaEptA 的氨基酸序列与脂 A PEA 转移酶（EptA）和 MCR 样蛋白家族共享 26.6%-33.1%的相似性，并定义了 12 个残基，这些残基有助于形成磷脂酰乙醇胺（PE）可识别的腔。RA-LZ01 和 RA-LZ01ΔRaEptA 中黏菌素耐药性的比较分析表明，黏菌素的水平从 96μg·mL 下降到 24~32μg·mL 。PE 结合腔的定点突变和突变体的表达显示，K309-rRaEptA 可以重塑大肠杆菌的表面，使其对黏菌素产生耐药性，表明 P309K 点突变是 EptA 介导的脂 A 修饰所必需的。此外，RA-LZ01ΔRaEptA 的毒力在体内和体外均比 RA-LZ01 减弱。总之，这些结果表明 RaEptA 参与了黏菌素耐药和致病性，而 P309K 突变可能改变了细菌的适应性，并增加了黏菌素耐药性从鸭疫里默氏杆菌向其他革兰氏阴性菌的传播。本研究的结果表明了另一种黏菌素耐药基因传播的情况，应该引起广泛关注。
