Plasmid-Borne Antimicrobial Resistance of Staphylococcus aureus Isolated in a Hospital in Lisbon, Portugal

Microb Drug Resist. 2016 Dec;22(8):617-626. doi: 10.1089/mdr.2015.0352. Epub 2016 Jun 16.


Plasmids play a key role in the genetic plasticity and survival of Staphylococcus aureus in challenging environments. Although many S. aureus plasmids have been described, still few studies portray the plasmid content of a given S. aureus population. The aim of this work was to characterize the plasmids carried by a collection of 53 S. aureus isolates collected in a large hospital in Lisbon, Portugal, and investigate their role in conferring resistance to several antimicrobial agents. Plasmids were present in 44 out of the 53 isolates and were grouped into eleven AccI restriction profiles. Plasmid curing of representative strains and comparison of antimicrobial susceptibility profiles between pairs of isogenic strains proved to be a valuable guidance tool in the identification of plasmid-located resistance genes. The plasmids harbored several resistance genes, namely blaZ (resistance to β-lactams), erm(C) (resistance to macrolides, lincosamides, and streptogramin B), cadA (resistance to cadmium and zinc), cadD (resistance to cadmium), and qacA and smr (resistance to biocides and dyes). This study demonstrates the impact of plasmids on the resistance properties of S. aureus, highlighting their role in the dissemination of antibiotic, heavy metal, and biocide resistance genes, and survival of this major pathogen in the hospital environment.

Keywords: Staphylococcus aureus; antibiotic; biocide; heavy metal; plasmid; resistance.

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism
  • Anti-Bacterial Agents / pharmacology
  • Antiporters / genetics
  • Antiporters / metabolism
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Gene Expression Regulation, Bacterial*
  • Hospitals
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism
  • Methyltransferases / genetics
  • Methyltransferases / metabolism
  • Microbial Sensitivity Tests
  • Multilocus Sequence Typing
  • Plasmids / chemistry
  • Plasmids / metabolism*
  • Portugal
  • Staphylococcal Infections / drug therapy
  • Staphylococcal Infections / microbiology
  • Staphylococcus aureus / drug effects
  • Staphylococcus aureus / genetics*
  • Staphylococcus aureus / growth & development
  • Staphylococcus aureus / isolation & purification


  • Anti-Bacterial Agents
  • Antiporters
  • Bacterial Proteins
  • Membrane Proteins
  • Membrane Transport Proteins
  • cadD protein, Staphylococcus aureus
  • small multidrug-resistance pump, Staphylococcus aureus
  • qacA protein, Staphylococcus aureus
  • Methyltransferases
  • rRNA (adenosine-O-2'-)methyltransferase
  • Adenosine Triphosphatases
  • cadmium translocating ATPase