Australian Group on Antimicrobial Resistance (AGAR) Australian Enterococcal Surveillance Outcome Program (AESOP)...

From 1 January to 31 December 2023, fifty-six institutions across Australia participated in the Australian Enterococcal Surveillance Outcome Program (AESOP). The aim of AESOP 2023 was to determine the proportion of enterococcal bacteraemia isolates in Australia that were antimicrobial resistant, and to determine the Enterococcus faecium molecular epidemiology. Of the 1,599 unique episodes of enterococcal bacteraemia investigated, 92.9% were caused by either E. faecalis (51.8%) or E. faecium (41.1%). Ampicillin and vancomycin resistance were not detected in E. faecalis but were detected in 94.2% and 50.8% of E. faecium respectively. Two linezolid-resistant E. faecalis were identified in 2023. Both isolates had linezolid minimum inhibitory concentrations (MICs) of 6.0 mg/L, were vancomycin susceptible, and harboured the optrA gene. Overall, 53.2% of E. faecium harboured either the vanA or the vanB gene; of these, 27.3% harboured vanA, 72.1% harboured vanB, and 0.6% harboured vanA and vanB. The percentage of vancomycin-resistant E. faecium bacteraemia isolates in Australia remains substantially higher than that recorded in most European countries. The E. faecium isolates consisted of 58 multi-locus sequence types (STs); 85.7% of isolates were classified into seven major STs, each containing ten or more isolates. All major STs belonged to clonal complex (CC) 17, a global hospital-adapted polyclonal E. faecium CC. The major STs (ST78, ST1424, ST17, ST80, ST796, ST1421 and ST555) were found across most regions of Australia, with ST78 identified in all regions. Overall, 58.3% of isolates belonging to the seven major STs harboured the vanA or vanB gene. AESOP 2023 has shown that enterococcal bacteraemia episodes in Australia continues to be frequently caused by polyclonal ampicillin-resistant high-level gentamicin-resistant vanA- or vanB-positive E. faecium which have limited treatment options.