Genomic Epidemiology of Clonal Complex 1 Staphylococcus aureus in Remote Western Australian Communities

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) was first reported in Western Australia (WA) in the 1990s. Although ST8-IVa [2B] (WA-5) was the first identified CA-MRSA in WA, ST1-IVa [2B] (WA-1) soon emerged as the dominant clone. To investigate the genomic epidemiology of clonal complex (CC) CC1 S. aureus in WA Aboriginal communities from 1995 to 2003 and assess the acquisition and diversity of the SCCmec element, whole genome sequencing was performed. Three sequence types (STs) were identified: ST1 (81.4%), ST761 (0.9%) and ST762 (17.8%). MRSA constituted 78% (n = 92) of the collection and all harboured SCCmec Type IVa [2B]. Panton-Valentine leukocidin (PVL)-encoding genes were identified in seven closely related isolates. The phylogenetic tree topology suggests the acquisition of the same SCCmec IV into the CC1 lineage occurred on two occasions. Bayesian coalescence analysis predicts the CC1 S. aureus lineage originated in WA more than 150 years ago. Dissemination of the CC1 S. aureus lineage, as well as the horizontal acquisition of SCCmec IV, may have been aided by the concurrent movement of Aboriginal inhabitants across different remote communities.