Prevalence of strain types and binary gene subtypes in an Australian Staphylococcus aureus cohort, 1989-2003

  • Sanmarié Schlebusch, Department of Microbiology, Pathology Queensland Central Laboratory, Herston Hospitals Complex, Brisbane, Qld, Australia, Australia
  • Ms Jacqueline Schooneveldt, Department of Microbiology, Pathology Queensland Central Laboratory, Herston Hospitals Complex, Brisbane, Qld, Australia, Australia
  • Dr Flavia Huygens, School of Life Sciences, Queensland University of Technology, Brisbane, Qld, Australia
  • Dr Graeme Nimmo, Department of Microbiology, Pathology Queensland Central Laboratory, Herston Hospitals Complex, Brisbane, Qld, Australia, Australia

    • Objective:
    To determine the changing prevalence of MRSA and MSSA and to establish the prevalence of Panton Valentine leukocidin (pvl) gene in an Australian Staphylococcus aureus cohort collected over two decades.

    Method:
    300 S. aureus isolates collected at Princess Alexandra Hospital for the Australian Group on Antimicrobial Resistance (AGAR) 1989, 1996 and 2003 surveys were examined. Isolates were assayed using real-time PCR for mecA, nuc and 16S rRNA, 8 single nucleotide polymorphisms (SNPs) derived from the seven housekeeping genes used in MLST and for five binary genes (pvl, cna, sdrE, pUB110, pT181). SNP profiles are concordant with MLST clonal complexes (CCs) and/or Sequence Types (STs). The presence or absence of the binary genes further divides the complexes in to subtypes.

    Results:
    SNP profiles correlated with 23 CCs/STs. The 90 MRSA isolates correlated with 3 CCs: CC239, CC1 and CC22. CC239 included 5 binary gene subtypes. The predominant strains for the 210 MSSA isolates were: CC45 (1989), CC78 (1996), and CC5 (2003). 9 MSSA isolates belonged to ST93. The pvl gene was only detected in 5 isolates of each year group.

    Conclusions:
    The proportion of pvl positive isolates was low and most of these belonged to ST93 and CC30. CC239 MRSA was the overall predominant strain and sole MRSA strain in 1989 and 1996. MRSA decreased significantly in 2003 in spite of the appearance of CC1 MRSA (WA-1) and CC22 MRSA (EMRSA-15). New binary gene subtypes appeared for the major MSSA STs CC45 and CC5 in 2003.