O'Brien Frances G, Yui Eto Karina, Murphy Riley J T, Fairhurst Heather M, Coombs Geoffrey W, Grubb Warren B, Ramsay Joshua P
CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia Australian Collaborating Centre for Enterococcus and Staphylococcus Species (ACCESS) Typing and Research, School of Veterinary Sciences and Life Sciences, Murdoch University and School of Biomedical Sciences, Curtin University, Perth, Western Australia, Australia.
CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia.
Nucleic Acids Res. 2015 Sep 18;43(16):7971-83. doi: 10.1093/nar/gkv755. Epub 2015 Aug 3.
Staphylococcus aureus is a common cause of hospital, community and livestock-associated infections and is increasingly resistant to multiple antimicrobials. A significant proportion of antimicrobial-resistance genes are plasmid-borne, but only a minority of S. aureus plasmids encode proteins required for conjugative transfer or Mob relaxase proteins required for mobilisation. The pWBG749 family of S. aureus conjugative plasmids can facilitate the horizontal transfer of diverse antimicrobial-resistance plasmids that lack Mob genes. Here we reveal that these mobilisable plasmids carry copies of the pWBG749 origin-of-transfer (oriT) sequence and that these oriT sequences facilitate mobilisation by pWBG749. Sequences resembling the pWBG749 oriT were identified on half of all sequenced S. aureus plasmids, including the most prevalent large antimicrobial-resistance/virulence-gene plasmids, pIB485, pMW2 and pUSA300HOUMR. oriT sequences formed five subfamilies with distinct inverted-repeat-2 (IR2) sequences. pWBG749-family plasmids encoding each IR2 were identified and pWBG749 mobilisation was found to be specific for plasmids carrying matching IR2 sequences. Specificity of mobilisation was conferred by a putative ribbon-helix-helix-protein gene smpO. Several plasmids carried 2-3 oriT variants and pWBG749-mediated recombination occurred between distinct oriT sites during mobilisation. These observations suggest this relaxase-in trans mechanism of mobilisation by pWBG749-family plasmids is a common mechanism of plasmid dissemination in S. aureus.
金黄色葡萄球菌是医院、社区及与家畜相关感染的常见病因，并且对多种抗菌药物的耐药性日益增强。相当一部分抗菌耐药基因由质粒携带，但只有少数金黄色葡萄球菌质粒编码接合转移所需的蛋白质或移动所需的Mob松弛酶蛋白。金黄色葡萄球菌接合性质粒的pWBG749家族可促进缺乏Mob基因的多种抗菌耐药性质粒的水平转移。在此，我们揭示这些可移动质粒携带pWBG749转移起始点（oriT）序列的拷贝，并且这些oriT序列可促进pWBG749介导的移动。在所有已测序的金黄色葡萄球菌质粒的一半中鉴定出了类似于pWBG749 oriT的序列，包括最常见的大型抗菌耐药/毒力基因质粒pIB485、pMW2和pUSA300HOUMR。oriT序列形成了具有不同反向重复序列2（IR2）的五个亚家族。鉴定出了编码每个IR2的pWBG749家族质粒，并且发现pWBG749的移动对携带匹配IR2序列的质粒具有特异性。移动的特异性由一个假定的带状螺旋-螺旋蛋白基因smpO赋予。几个质粒携带2 - 3个oriT变体，并且在移动过程中，pWBG749介导的重组发生在不同的oriT位点之间。这些观察结果表明，pWBG749家族质粒的这种反式松弛酶移动机制是金黄色葡萄球菌中质粒传播的常见机制。
