The Continuing Evolution of Community-Associated MRSA ST93-IV in Australia

Abstract

BackgroundThe global emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has seen the dominance of specific clones in different regions around the world with the PVL-positive ST93-IV as the predominant CA-MRSA clone in Australia. In this study we applied a genome-wide association study (GWAS) approach on a collection of Australian ST93-IV MRSA genomes to identify genetic traits that may have assisted the ongoing transmission of ST93-IV in Australia. We also compared the genomes of ST93-IV bacteraemia and non-bacteraemia isolates to identify potential virulence factors associated with bacteraemia.ResultsBased on single nucleotide polymorphism phylogenetics we identified two distinct ST93-IV clades circulating concurrently in Australia. One of the clades contained isolates primarily isolated in the northern regions of Australia whilst isolates in the second clade were distributed across the country. Analyses of the ST93-IV genome plasticity over a 15-year period (2002-2017) revealed an observed gain in accessory genes amongst the clone’s population. The GWAS analysis on the bacteraemia identified two genes that have also previously been associated to this kind of infection. ConclusionsThe emergence of a ST93-IV clade containing additional virulence genes may explain the high prevalence of ST93-IV infections amongst the indigenous population living in the northern regions of Australia. In summary, this study has shown ST93-IV is evolving with multiple additional genes possibly contributing to its dominance in the Australian community.