Two B/O plasmids were sequenced. The kanamycin resistance plasmid R805a was found in a Salmonella Typhi strain from a 1972 typhoid fever outbreak in Mexico City. pCERC6, which confers resistance to ampicillin, streptomycin and sulphamethoxazole, was found in a commensal E. coli isolated from a healthy adult in Sydney in 2008. Both plasmids contain the same gene for RNAI, the incompatibility determinant, as the reference B/O plasmid pMU707 and the recently reported plasmid p838B-R, which came from a commensal E. coli isolated in Sydney in 2004. However, three different repA alleles are associated with the IncB/O rnaI. Whereas the repA gene of p838B-R is identical to that of pMU707, R805a and pCERC6 each carry a different repA. Comparison of the plasmid backbones revealed that R805a has a different oriT-nikAB region to that in pCERC6 and p838B-R, encoding different NikA relaxosome accessory factors and NikB relaxases. The different nikA genes were associated with oriT sites that differed in the sequences of their long, imperfect inverted repeats. A further 11 publicly available complete plasmid sequences contain the same B/O rnaI, with either the repA of pMU707/p838B-R or of R805a, and the oriT-nikAB region of p838B-R/pCERC6 or of R805a. All four possible combinations were seen. Extensive variation was also observed in the traY-excA entry exclusion region, and in the locations of mobile elements, including ones carrying antibiotic resistance genes. Plasmids that contain the same rnaI gene would be considered the same by a number of typing methods, but this study has unveiled previously unnoticed mosaicism in the backbones of one such group. This highlights the importance of considering entire plasmid backbones for the typing and tracking of specific lineages.

中文翻译：

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对两个B / O质粒（1972年的R805a和2008年的pCERC6）的分析显示，B / O质粒主链具有广泛的镶嵌性。

对两个B / O质粒进行测序。卡那霉素抗性质粒R805a在1972年墨西哥城爆发伤寒的沙门氏菌中发现。2008年在悉尼健康成年人体内分离出的共生大肠杆菌中发现了对氨苄青霉素，链霉素和磺胺甲恶唑具有抗性的pCERC6。这两个质粒均含有不相容决定簇RNAI的相同基因，作为参考B / O质粒pMU707和最近报道的质粒p838B-R来自2004年在悉尼分离的普通大肠杆菌。但是，三个不同的repA等位基因与IncB / O rnaI相关。尽管p838B-R的repA基因与pMU707的相同，但R805a和pCERC6各自带有不同的repA。质粒主链的比较显示，R805a与pCERC6和p838B-R具有不同的oriT-nikAB区，编码不同的NikA松弛体辅助因子和NikB松弛酶。不同的nikA基因与oriT位点相关，这些oriT位点的长且不完美的反向重复序列不同。另外11个可公开获得的完整质粒序列包含相同的B / O rnaI，即pMU707 / p838B-R或R805a的repA，以及p838B-R / pCERC6或R805a的oriT-nikAB区。看到了所有四种可能的组合。在traY-excA进入排斥区域和活动元件（包括携带抗生素抗性基因的元件）的位置也观察到广泛的变异。包含相同rnaI基因的质粒在许多分型方法中都被认为是相同的，但是这项研究揭示了以前未注意到的在此类组别骨架中的镶嵌现象。