Typing MRSA isolates from hospital outbreaks: PFGE and SNP (single nucleotide polymorphism) and binary gene analysis

  • Vikram Vaska, Dept of Microbiology, Pathology Queensland, Herston Hospitals Campus HERSTON QLD 4029 AUSTRALIA, Australia
  • Ms Jacqueline Schooneveldt, Dept of Microbiology, Pathology Queensland, Herston Hospitals Campus HERSTON QLD 4029 AUSTRALIA, Australia
  • Dr Flavia Huygens, School of Life Sciences, Queensland University of Technology, Brisbane, Qld, Australia
  • A/Prof Graeme Nimmo, Dept of Microbiology, Pathology Queensland, Herston Hospitals Campus HERSTON QLD 4029 AUSTRALIA, Australia

    • Objective:
    This study compared PFGE and SNP / binary genotyping results from MRSA isolates from 2 hospital outbreaks. PFGE is well established in outbreak investigations. Some newer DNA sequence based typing methods are less discriminatory for this purpose but more efficient. A real-time PCR Staphylococcus aureus genotyping method using 7 SNPs and binary gene (pvl, pUB110, cna, SdrE and PT181) analysis has been reported by our group.

    Method:
    MRSA isolates from two outbreaks in Brisbane (Queensland, Australia) tertiary hospitals were assessed separately (hospital A n=17, B n=8). Sma1 restricted DNA PFGE was performed, with types assigned for isolates with >80% similarity (Dice coefficient). SNP / binary genotyping which corresponds to sequence types (ST) and / or clonal complexes (CC) for epidemiological analysis was performed as reported.

    Results:
    PFGE determined a different outbreak strain for outbreaks A (14 of 17 isolates) and B (5/8) with other strains unique. All isolates had the same SNP derived MLST (ST239). For A, the common type had binary gene profile 00110 with the other 3; 01110. For B, 7 were binary profile 01110, with one unique strain 00110. PFGE appeared more discriminatory than SNP / binary typing.

    Conclusion:
    MRSA SNP / binary genotyping had variable discriminatory performance when applied to small hospital outbreaks. Additional gene sequence informative PCR (high resolution melt analysis (HRM)) is planned to improve its utility.