Background Vancomycin resistance is mostly associated with Enterococcus faecium due to Tn1546-vanA located on narrow- and broad-host plasmids of various families. This study’s aim was to analyse the effects of acquiring Tn1546-carrying plasmids with proven epidemicity in different bacterial host backgrounds. Methods Widespread Tn1546-carrying plasmids of different families RepA_N (n = 5), Inc18 (n = 4) and/or pHTβ (n = 1), and prototype plasmids RepA_N (pRUM) and Inc18 (pRE25, pIP501) were analysed. Plasmid transferability and fitness cost were assessed using E. faecium (GE1, 64/3) and Enterococcus faecalis (JH2-2/FA202/UV202) recipient strains. Growth curves (Bioscreen C) and Relative Growth Rates were obtained in the presence/absence of vancomycin. Plasmid stability was analysed (300 generations). WGS (Illumina-MiSeq) of non-evolved and evolved strains (GE1/64/3 transconjugants, n = 49) was performed. SNP calling (Breseq software) of non-evolved strains was used for comparison. Results All plasmids were successfully transferred to different E. faecium clonal backgrounds. Most Tn1546-carrying plasmids and Inc18 and RepA_N prototypes reduced host fitness (–2% to 18%) while the cost of Tn1546 expression varied according to the Tn1546-variant and the recipient strain (9%–49%). Stability of Tn1546-carrying plasmids was documented in all cases, often with loss of phenotypic resistance and/or partial plasmid deletions. SNPs and/or indels associated with essential bacterial functions were observed on the chromosome of evolved strains, some of them linked to increased fitness. Conclusions The stability of E. faecium Tn1546-carrying plasmids in the absence of selective pressure and the high intra-species conjugation rates might explain the persistence of vancomycin resistance in E. faecium populations despite the significant burden they might impose on bacterial host strains.

中文翻译：

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与医院感染爆发相关的耐万古霉素粪肠球菌质粒的适应性成本

背景万古霉素耐药性主要与粪肠球菌有关，因为 Tn1546-vanA 位于各种家族的窄宿主和宽宿主质粒上。本研究的目的是分析在不同细菌宿主背景中获得具有流行性的携带 Tn1546 的质粒的效果。方法分析了不同家族 RepA_N (n = 5)、Inc18 (n = 4) 和/或 pHTβ (n = 1) 的广泛携带 Tn1546 的质粒，以及原型质粒 RepA_N (pRUM) 和 Inc18 (pRE25, pIP501)。使用粪肠球菌 (GE1, 64/3) 和粪肠球菌 (JH2-2/FA202/UV202) 受体菌株评估质粒可转移性和适应性成本。在存在/不存在万古霉素的情况下获得生长曲线（Bioscreen C）和相对生长速率。分析质粒稳定性（300 代）。进行了非进化和进化菌株（GE1/64/3 转导子，n = 49）的 WGS（Illumina-MiSeq）。非进化菌株的 SNP 调用（Breseq 软件）用于比较。结果所有质粒均成功转移至不同的粪肠球菌克隆背景。大多数携带 Tn1546 的质粒以及 Inc18 和 RepA_N 原型降低了宿主适应性（–2% 至 18%），而 Tn1546 表达的成本因 Tn1546 变体和受体菌株而异（9%–49%）。在所有情况下都记录了携带 Tn1546 的质粒的稳定性，通常伴有表型抗性丧失和/或部分质粒缺失。在进化菌株的染色体上观察到与基本细菌功能相关的 SNP 和/或插入缺失，其中一些与增加的适应度有关。结论 E.的稳定性。