National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, P. R. China; College of Veterinary Medicine, South China Agricultural University, Guangzhou, P. R. China; Department of Animal Science, The University of Tennessee, Knoxville, TN, USA.
National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, P. R. China; College of Veterinary Medicine, South China Agricultural University, Guangzhou, P. R. China.
Int J Antimicrob Agents. 2020 Jan;55(1):105806. doi: 10.1016/j.ijantimicag.2019.09.010. Epub 2019 Sep 15.
To characterize the colistin-resistant bacterial population in the gut and assess diversity of mcr-1 transmission within a single individual.
Large numbers of isolates (>100 colonies/chicken cecum sample) were collected from nine randomly selected mcr-1-positive chickens in China and used for comprehensive microbiological, molecular and comparative genomics analyses.
Of 1273 colonies, 968 were mcr-1 positive (962 Escherichia coli, two Escherichia fergusonii, two Klebsiella pneumoniae and two Klebsiella quasipneumoniae). One to six colistin-resistant species and three to 10 E. coli pulsed-field gel electrophoresis (PFGE) clusters could be identified from each sample. Whole-genome sequencing (WGS) analysis of the representative E. coli strains revealed three to nine sequence types observed in a single chicken host. The mcr-1 genes are located in either chromosomes or plasmids of different types, including IncI2 (n=30), IncHI2 (n=14), IncX4 (n=4), p0111(n=2) and IncHI1(n=1). Strikingly, in single cecum samples, one to five Inc type plasmids harbouring mcr-1 could be identified. Great diversity was also observed for the same IncI2 plasmid within a single chicken host. In addition, up to eight genetic contexts of the mcr-1 gene occurred within a single chicken.
There is extensive heterogeneity and flexibility of mcr-1 transmission in chicken gut due to bacterial species differences, distant clonal relatedness of isolates, many types and variations of mcr-positive plasmids, and the flexible genetic context of the mcr-1 gene. These compelling findings indicate that the gut is a 'melting pot' for active horizontal transfer of the mcr-1 gene.
描述肠道中粘菌素耐药细菌群体的特征，并评估单个个体中 mcr-1 传播的多样性。
从中国随机选择的 9 只 mcr-1 阳性鸡中收集了大量分离株（每个鸡盲肠样本>100 个菌落），并用于全面的微生物学、分子和比较基因组学分析。
在 1273 个菌落中，968 个为 mcr-1 阳性（962 株大肠埃希菌、2 株弗格森埃希菌、2 株肺炎克雷伯菌和 2 株产酸克雷伯菌）。每个样本可鉴定出 1 到 6 种粘菌素耐药种和 3 到 10 个大肠埃希菌脉冲场凝胶电泳（PFGE）簇。代表大肠埃希菌菌株的全基因组测序（WGS）分析显示，在单个鸡宿主中观察到 3 到 9 种序列类型。mcr-1 基因位于不同类型的染色体或质粒中，包括 IncI2（n=30）、IncHI2（n=14）、IncX4（n=4）、p0111（n=2）和 IncHI1（n=1）。引人注目的是，在单个盲肠样本中，可以鉴定出 1 到 5 种携带 mcr-1 的 Inc 型质粒。在单个鸡宿主中，同样的 IncI2 质粒也存在很大的多样性。此外，单个鸡体内 mcr-1 基因的遗传环境多达 8 种。
由于细菌种间差异、分离株的远缘克隆相关性、mcr-1 阳性质粒的多种类型和变化以及 mcr-1 基因的灵活遗传环境，鸡肠道中 mcr-1 的传播存在广泛的异质性和灵活性。这些令人信服的发现表明，肠道是 mcr-1 基因主动水平转移的“大熔炉”。
