IncI2 type plasmids are medium-sized (~55-80 kb) conjugative plasmids that have been found carrying important antimicrobial resistance genes but have also been frequently found as cryptic plasmids. The DNA sequences for 147 fully sequenced IncI2 plasmids were studied by a whole-plasmid multi-locus sequence typing (wpMLST) scheme. A total of 171 loci were identified of which 52 were considered core (carried by greater than 95% of the plasmids). Most of the plasmids carrying the antimicrobial gene mcr-1 were in a distinct clade while most of the antimicrobial gene free plasmids were more distantly related. However, the host strains of bacteria were disparate for both groups of plasmids, showing that conjugal transfer of IncI2 plasmid is frequent. The mcr-1 gene was likely to have been introduced into IncI2 plasmids multiple times. It was also observed that the genes for conjugation showed significant linkage disequilibrium despite substantial diversity for most of those genes. Genes associated with biofilm formation were also among the core genes. The core genes can be considered the cohesive unit that defines the IncI2 plasmid group. Given the role conjugation can play in biofilm formation, it was concluded that conjugation is an active survival strategy for IncI2 plasmids. The IncI2 plasmid will have selective advantage when the plasmid-bearing bacteria are introduced to a new animal host that carries potential conjugal mates.

中文翻译：

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全质粒多基因座序列分型显示了IncI2质粒的生物学特性。

IncI2型质粒是中等大小（〜55-80 kb）的结合质粒，已发现其携带重要的抗药性基因，但也经常被发现为隐性质粒。通过全质粒多基因座序列分型（wpMLST）方案研究了147个完全测序的IncI2质粒的DNA序列。总共鉴定出171个基因座，其中52个被认为是核心基因（携带了超过95％的质粒）。携带抗微生物基因mcr-1的大多数质粒都位于不同的进化枝中，而大多数无抗微生物基因的质粒则具有更远的相关性。然而，细菌的宿主菌株对于两组质粒而言是完全不同的，表明IncI2质粒的结合转移是频繁的。mcr-1基因可能已多次引入IncI2质粒。还观察到，尽管大多数那些基因具有相当大的多样性，但是用于缀合的基因显示出显着的连锁不平衡。与生物膜形成相关的基因也在核心基因中。核心基因可视为定义IncI2质粒组的内聚单元。鉴于缀合可以在生物膜形成中发挥作用，因此得出的结论是，缀合是IncI2质粒的一种主动存活策略。当将携带质粒的细菌引入携带潜在伴侣的新动物宿主中时，Incl2质粒将具有选择优势。核心基因可视为定义IncI2质粒组的内聚单元。鉴于缀合可以在生物膜形成中发挥作用，因此得出的结论是，缀合是IncI2质粒的一种主动存活策略。当将携带质粒的细菌引入携带潜在伴侣的新动物宿主中时，Incl2质粒将具有选择优势。核心基因可视为定义IncI2质粒组的内聚单元。鉴于缀合可以在生物膜形成中发挥作用，因此得出的结论是，缀合是IncI2质粒的一种主动存活策略。当将携带质粒的细菌引入携带潜在伴侣的新动物宿主中时，Incl2质粒将具有选择优势。