Clonal complex 75: investigating a novel Staphylococcus lineage

  • Deborah Holt, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia
  • Ms Rachael Lilliebridge, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia
  • Ms Annette Dougall, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia
  • Dr Steven Tong, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia
  • Dr Malcolm McDonald, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia
  • Prof Bart Currie, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia
  • A/Prof Philip Giffard, Menzies School of Health Research, Institute of Advanced Studies, Charles Darwin University, Darwin, Australia, Australia

    • Objective
    To investigate clonal complex 75, a novel type of Staphylococcus which is efficiently circulating in remote Aboriginal communities in the Northern Territory of Australia.

    Methods
    Community associated S. aureus isolates were collected as part of a community surveillance program of skin bacterial infections in four remote Aboriginal communities in the Northern Territory. Isolates were assigned to a clonal complex (CC) representative of the major S. aureus lineages using a kinetic real time PCR method which interrogates seven informative SNPs in the loci used for Multi Locus Sequence Typing (MLST) of S. aureus.

    Results
    The most common type of S. aureus found was a novel type designated CC75. These isolates accounted for 23% (98/434) of all isolates and 70% (62/89) of methicillin resistant isolates recovered. 63% (62/98) of the CC75 isolates collected were shown to possess the methicillin resistance determinant SCCmec. Isolates with SCCmec type IV and type V were identified, indicating that SCCmec may have been acquired by CC75 isolates on several independent occasions.
    Sequence analysis revealed that CC75 isolates are significantly genetically different to other S. aureus. MLST alleles of S. aureus are at least 97% identical. However CC75 MLST alleles are only 90-95% identical to the corresponding alleles in other S. aureus. Diversity within the CC75 MSLT alleles was also shown.
    CC75 isolates were subsequently identified in a collection of hospital S. aureus isolates and were shown to be capable of causing significant disease.

    Conclusions
    We hypothesise that CC75 is not a clone of S. aureus but is rather a genetically distinct Staphylococcus species. Preliminary evidence indicates that CC75 isolates are a diverse group with closely related genotypes. CC75 may well encompass a similar degree of diversity to S. aureus. CC75 is capable of causing disease in community and hospital settings.