HicBA 和一个新的毒素-抗毒素样系统 TsxAB 在大肠杆菌中 IncX4 耐药质粒稳定性中的作用。

The roles of HicBA and a novel toxin-antitoxin-like system, TsxAB, in the stability of IncX4 resistance plasmids in Escherichia coli.

机构信息

Centre for Infectious Diseases and Microbiology, The Westmead Institute for Medical Research, The University of Sydney, Westmead Hospital, Westmead, NSW, Australia.

出版信息

J Antimicrob Chemother. 2019 Mar 1;74(3):553-556. doi: 10.1093/jac/dky491.

DOI:10.1093/jac/dky491

PMID:30535076

Abstract

OBJECTIVES

To identify toxin-antitoxin (TA)-like plasmid stability loci on IncX4 plasmids.

METHODS

TA-like loci were identified bioinformatically and their contribution to stability of the IncX4 plasmid pJIE143 was tested in optimal growth conditions in vitro. The conservation of the TA-like loci identified was analysed within an updated IncX plasmid database.

RESULTS

A novel TA-like locus, tsxAB, was identified on the IncX4 plasmid pJIE143, carrying the important plasmid-borne antibiotic resistance gene blaCTX-M-15. pJIE143 (the WT plasmid) and its tsxA mutant are stable for 80 bacterial generations in the absence of selective pressure but a tsxB deletion mutant of pJIE143 is relatively quickly lost without positive selection (91.1% ± 1.5% loss after 50 generations). Nine IncX subclasses were identified among 272 fully sequenced IncX plasmids, dominated by those identified as IncX3, IncX1 and IncX4 subclasses in PlasmidFinder. The novel TA-like locus, tsxAB, appears to be a feature of IncX4 plasmids, being present in 64 of 67 so identified, but only present in a single IncX1 plasmid (of 79 identified) and present in no other IncX plasmids.

CONCLUSIONS

tsxAB, a novel TA-like stability locus, is highly conserved in IncX4 plasmids associated with transmission of important antibiotic resistance genes. Previous in silico analysis indicated that IncX4 encodes only HicBA among the known TA systems. Here we show that HicBA does not contribute to plasmid stability in optimal growth conditions for Escherichia coli and instead demonstrate this role for a completely novel TA-like system, TsxAB, that appears both necessary and sufficient for E. coli addiction to IncX4 resistance plasmids.

摘要

目的

鉴定 IncX4 质粒上的毒素-抗毒素（TA）样质粒稳定基因座。

方法

通过生物信息学方法鉴定 TA 样基因座，并在体外最佳生长条件下测试它们对 IncX4 质粒 pJIE143 的稳定性的贡献。在所更新的 IncX 质粒数据库中分析了鉴定出的 TA 样基因座的保守性。

结果

在 IncX4 质粒 pJIE143 上鉴定出一个新的 TA 样基因座 tsxAB，该基因座携带重要的质粒携带的抗生素耐药基因 blaCTX-M-15。pJIE143（WT 质粒）及其 tsxA 突变体在没有选择压力的情况下，在 80 个细菌世代中保持稳定，但 pJIE143 的 tsxB 缺失突变体在没有正选择的情况下很快丢失（50 代后丢失 91.1%±1.5%）。在 272 个完全测序的 IncX 质粒中鉴定出 9 个 IncX 亚类，其中以 PlasmidFinder 鉴定的 IncX3、IncX1 和 IncX4 亚类为主。新的 TA 样基因座 tsxAB 似乎是 IncX4 质粒的一个特征，在 67 个鉴定的 IncX4 质粒中都存在，但只存在于一个 IncX1 质粒（79 个鉴定的质粒中）中，而不存在于其他 IncX 质粒中。

结论

tsxAB 是一个新的 TA 样稳定性基因座，在与重要抗生素耐药基因传播相关的 IncX4 质粒中高度保守。先前的计算机分析表明，IncX4 编码的仅 HicBA 是已知 TA 系统之一。在这里，我们表明 HicBA 在大肠杆菌的最佳生长条件下对质粒稳定性没有贡献，而是证明了这种作用是由一个全新的 TA 样系统 TsxAB 引起的，该系统对大肠杆菌对 IncX4 耐药质粒的成瘾性是必要和充分的。