Data_Sheet_1_blaCTX–M–1/IncI1-Iγ Plasmids Circulating in Escherichia coli From Norwegian Broiler Production Are Related, but Distinguishable.PDF

Escherichia coli carrying blaCTX–M–1 mediating resistance to extended-spectrum cephalosporins was recently described as a new genotype in Norwegian broiler production. The aim of this study was to characterize these isolates (n = 31) in order to determine whether the emergence of the genotype was caused by clonal expansion or horizontal dissemination of blaCTX–M–1-carrying plasmids. All included isolates were subjected to whole genome sequencing. Plasmid transferability was determined by conjugation, and plasmid replicons in the transconjugants were described using PCR-based replicon typing. Plasmid sizes were determined using S1 nuclease digestion. Plasmids in a subset of strains were reconstructed and compared to plasmids from broiler production in other European countries. The isolates belonged to nine different sequence types (STs), with the largest group being ST57 (n = 12). The vast majority of blaCTX–M–1-carrying plasmids were conjugative. All transconjugants were positive for the IncI1-Iγ replicon, and several also harbored the IncFIB replicon. Highly similar plasmids were present in different E. coli STs. Additionally, high similarity to previously published plasmids was detected. A reconstructed plasmid from an ST57 isolate harbored both IncI1-Iγ and IncFIB replicons and was considered to be co-integrated. The presence of one large plasmid was confirmed by S1 nuclease digestion. Our results show that dissemination of blaCTX–M–1 in Norwegian broiler production is due to both clonal expansion and horizontal transfer of plasmids carrying blaCTX–M–1. The blaCTX–M–1/IncI1-Iγ plasmids grouped into two main lineages, namely clonal complex (CC)-3 and CC-7. The genetic diversity at both strain and plasmid level indicates multiple introductions to Norway. We also show that the blaCTX–M–1 plasmids circulating in Norwegian broiler production are highly similar to plasmids previously described in other countries.

携带blaCTX-M-1基因、介导超广谱头孢菌素耐药的大肠埃希菌（Escherichia coli），近期在挪威肉鸡养殖业中被报道为一种新型基因型。本研究旨在对31株此类分离株进行特征分析，以明确该基因型的出现是由blaCTX-M-1阳性质粒的克隆扩增还是水平传播所导致。所有纳入研究的分离株均接受全基因组测序。通过接合试验测定质粒的接合转移性，并采用基于PCR的质粒复制子分型技术对接合子中的质粒复制子进行鉴定。通过S1核酸酶酶切法测定质粒分子量大小。对部分菌株的质粒进行重构，并与其他欧洲国家肉鸡养殖业中分离到的质粒进行比对。该批分离株隶属于9种不同的序列型（sequence types, STs），其中数量最多的群组为ST57（共12株）。绝大多数携带blaCTX-M-1的质粒均可接合。所有接合子均携带IncI1-Iγ复制子，部分菌株还同时携带有IncFIB复制子。不同大肠埃希菌ST型中均存在高度相似的质粒。此外，还检测到与此前已发表的质粒具有高度同源性的序列。一株来自ST57分离株的重构质粒同时携带有IncI1-Iγ和IncFIB复制子，被判定为共整合质粒。S1核酸酶酶切结果证实了该大质粒的存在。本研究结果显示，挪威肉鸡养殖业中blaCTX-M-1基因的传播，同时由克隆扩增与携带blaCTX-M-1的质粒水平转移共同介导。blaCTX-M-1/IncI1-Iγ质粒可分为两个主要谱系，即克隆复合体（clonal complex, CC）-3与CC-7。菌株与质粒水平上均存在遗传多样性，表明该基因型曾多次传入挪威。本研究同时证实，挪威肉鸡养殖业中流行的blaCTX-M-1质粒，与此前其他国家报道的质粒具有高度相似性。