title: Origin-of-transfer sequences facilitate mobilisation of non-conjugative antimicrobial-resistance plasmids in Staphylococcus aureus.
abstract: 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.
authors.affiliation: 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.
authors.forename: Frances G
authors.initials: FG
authors.lastname: O'Brien
authors.affiliation: CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia.
authors.forename: Karina
authors.initials: K
authors.lastname: Yui Eto
authors.affiliation: CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia.
authors.forename: Riley J T
authors.initials: RJ
authors.lastname: Murphy
authors.affiliation: CHIRI Biosciences Precinct, School of Biomedical Sciences, Faculty of Health Sciences, Curtin University, Bentley WA 6102, Australia.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Fairhurst
authors.affiliation: 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 PathWest Laboratory Medicine, Fiona Stanley Hospital, Perth, Western Australia, Australia.
authors.forename: Geoffrey W
authors.initials: GW
authors.lastname: Coombs
authors.affiliation: 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.
authors.forename: Warren B
authors.initials: WB
authors.lastname: Grubb
authors.affiliation: 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 josh.ramsay@curtin.edu.au.
authors.forename: Joshua P
authors.initials: JP
authors.lastname: Ramsay
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D003227:Conjugation, Genetic; D017124:Conserved Sequence; D004269:DNA, Bacterial / Q000737:chemistry*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D055029:Inverted Repeat Sequences; D010957:Plasmids / Q000235:genetics*; D011995:Recombination, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013211:Staphylococcus aureus / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial