From 1 January to 31 December 2019, thirty-nine institutions around Australia participated in the Australian Enterococcal Sepsis Outcome Programme (AESOP). The aim of AESOP 2019 was to determine the proportion of enterococcal bacteraemia isolates in Australia that were antimicrobial resistant, and to characterise the molecular epidemiology of the E. faecium isolates. Of the 1,361 unique episodes of bacteraemia investigated, 95.2% were caused by either E. faecalis (51.4%) or E. faecium (43.8%). Ampicillin resistance was not detected in E. faecalis but was detected in 91.1% of E. faecium. Vancomycin non-susceptibility was detected in 0.1% of E. faecalis and in 41.8% of E. faecium. Overall, 45.4% of E. faecium harboured vanA and /or vanB genes. For the vanA / vanB positive E. faecium isolates, 49.1% harboured vanA genes only and 50.6% vanB genes; 0.3% harboured both vanA and vanB genes. The percentage of E. faecium bacteraemia isolates resistant to vancomycin in Australia is substantially higher than that seen in most European countries. E. faecium consisted of 78 multilocus sequence types (STs), of which 75.0% of isolates were classified into six major STs containing ten or more isolates. All major STs belong to clonal cluster (CC) 17, a major hospital-adapted polyclonal E. faecium cluster. The predominant STs (ST1424, ST17, ST796, ST80, ST1421, and ST78) were found across most regions of Australia. The most prevalent clone was ST1424, which was identified in all regions except the Northern Territory and Western Australia. Overall, 51.4% of isolates belonging to the six predominant STs harboured vanA or vanB genes. In 2019, AESOP has shown that enterococcal bacteraemias in Australia are frequently caused by polyclonal ampicillin-resistant high-level gentamicin-resistant vanA or vanB E. faecium which have limited treatment options
