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 screen for genetic traits that might have assisted the ongoing transmission of ST93-IV in Australia. We also compared the genomes of ST93-IV bacteraemia and non-bacteraemia isolates to search for potential virulence genes associated with bacteraemia.ResultsBased on single nucleotide polymorphism phylogenetics we revealed 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. GWAS analysis on the bacteraemia isolates identified two gene candidates that have previously been associated to this kind of infection.ConclusionsAlthough this hypothesis was not tested here, it is possible that the emergence of a ST93-IV clade containing additional virulence genes might be related to the high prevalence of ST93-IV infections amongst the indigenous population living in the northern regions of Australia. More importantly, our data also demonstrated that GWAS can reveal candidate genes for further investigations on the pathogenesis and evolution of MRSA strains within a same lineage.
Highlights
The 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 Panton-Valentine leukocidin (PVL)-positive ST93-IV as the predominant CA-MRSA clone in Australia
The nonbacteraemia isolates were limited to four geographical regions: New South Wales, Victoria, Western Australia and Northern Territory
Based on core genome Single Nucleotide Polymorphisms (SNP), the rooted phylogeny based on 1383 SNPs depicted the ST93 population to cluster primarily in two main clades (Fig. 1)
Summary
The 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. Over the last three decades, community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged globally. A small number of CA-MRSA clones are dominant in different regions of the world such as multilocus sequence type (ST) 8-IV (USA300) in North America, ST80-IV in Europe and Northern Africa, ST59-IV/V in Asia, ST772-V and ST22-IV in the Indian subcontinent, and ST30-IV in the West Pacific region [1]. Transmission of the dominant clones in other regions has occurred, and characteristically they harbour the lukS/F-PV genes that encode the Panton-Valentine leukocidin (PVL) toxin [2].
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