A three-year whole genome sequencing perspective of Enterococcus faecium sepsis in Australia

BACKGROUND: Over the last three decades, hospital adapted clonal complex (CC) 17 strains of Enterococcus faecium have acquired and exchanged antimicrobial resistance genes leading to the widespread resistance to clinically important antimicrobials globally. In Australia, a high prevalence of vancomycin resistance has been reported in E. faecium in the last decade. METHODS: In this study, we determined the phylogenetic relationship and genetic characteristics of E. faecium collected from hospitalized patients with blood stream infections throughout Australia from 2015 to 2017 using high throughput molecular techniques. RESULTS: Using single nucleotide polymorphism based phylogenetic inference, three distinct clusters of isolates were observed with additional sub-clustering. One cluster harboured mostly non-CC17 isolates while two clusters were dominant for the vanA and vanB operons. CONCLUSION: The gradual increase in dominance of the respective van operon was observed in both the vanA and vanB dominant clusters suggesting a strain-van operon affinity. The high prevalence of the van operon within isolates of a particular sub-cluster was linked to an increased number of isolates and 30-day all-cause mortality. Different dominant sub-clusters were observed in each region of Australia. Findings from this study can be used to put future surveillance data into a broader perspective including the detection of novel E. faecium strains in Australia as well as the dissemination and evolution of each strain.