Microarray analysis of Staphylococcus aureus colonising people in remote Western Australian communities

  • Frances O'Brien, Gram-positive Bacteria Typing and Research Unit, Curtin University of Technology, Western Australia, Australia
  • Mr Kong Chew, Curtin University of Technology, Western Australia, Australia
  • Mr Geoffrey Coombs, Gram-positive Bacteria Typing and Research Unit, PathWest Laboratory Medicine – WA, Royal Perth Hospital, Australia, Australia
  • A/Prof Keryn Christiansen, Gram-positive Bacteria Typing and Research Unit,PathWest Laboratory Medicine – WA, Royal Perth Hospital, Australia, Australia
  • Prof Warren Grubb, Gram-positive Bacteria Typing and Research Unit, Curtin University of Technology, Western Australia, Australia

    • Background: In Western Australia (WA) community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), initially observed in remote Indigenous communities, are now isolated throughout the State. In the remote communities the essential genetic background of colonising S aureus consists of 21 multilocus sequence type (MLST) clones belonging to 13 Clonal Complexes (CCs) and two Singleton lineages. Only five of the CCs contain CA-MRSA, of which three have subsequently become the predominant CA-MRSA found in the general WA community.
    Methods: To understand more about CA-MRSA in WA representative methicillin-resistant and -sensitive clones of the 21 S. aureus MLST types colonising people in the remote communities were tested with the Clondiag Array tube system. Species marker, agr type, antibiotic resistance, enterotoxin, toxin, leukocidin, haemolysin, protease and exotoxin-like genes were investigated.
    Results: All agr types were present in the population investigated and there were two non-typable clones. Of the determinants that were detected by the array few resistance determinants were found. In addition to the mecA gene the CA-MRSA harboured more resistance determinants than the CA-MSSA. All clones had different complements of virulence genes, with isolates within the same CC having similar but not identical gene profiles. Of the five CCs that contained CA-MRSA three of the CA-MRSA had more virulence determinants than their counterpart CA-MSSA and two had less. Enterotoxin genes from the enterotoxin gene cluster were present in only five of the S. aureus CCs, and furthermore, the gene content of the cluster was similar in all positive clones. The Panton-Valentine leukocidin was found in two CA-MSSA clones, and one CA-MRSA harboured the toxic shock syndrome toxin-1 gene.
    Conclusions: There is considerable diversity of agr types and virulence gene profiles amongst S. aureus colonising people in remote communities in WA. The only array-based genetic element that was found exclusively in all CA-MRSA was the mecA resistance gene.