Antimicrobial resistance in Staphylococcus aureus and Enterococci spp. isolates from bloodstream infections in Australian children, 2013 - 2021.

Background: Rising proportions of antimicrobial resistance (AMR) have been observed in both Staphylococcus aureus and Enterococcus spp. isolates.

Methods: The Australian Group on Antimicrobial Resistance (AGAR) surveillance program captures clinical and microbiological data of isolates detected in blood cultures across Australia. EUCAST 2022 was used for MIC interpretation and the AMR package in R for data analysis.

Results: There were 2,091 BSIs with S. aureus and 534 enterococcal BSI episodes over the nine years. Three-quarters of S. aureus BSI episodes were community-onset (78.3%) whilst more than half of enterococcal BSIs were hospital-onset (56.9%). The median age for S. aureus BSIs was 6 years, whilst >50% enterococcal BSIs were in children <12 months old.Fifteen percent of S. aureus isolates were methicillin-resistant (MRSA). Overall, 85.3% of S. aureus were resistant to penicillin, 12.5% resistant to erythromycin, 10.3% to clindamycin, and 4.7% to ciprofloxacin. Resistance to penicillin decreased over time whilst clindamycin resistance increased.Resistance in Enterococcus spp. was almost entirely observed in E. faecium; only one E. faecalis isolate was ampicillin resistant, and no E. faecalis isolates were vancomycin or teicoplanin resistant. Seventy-three percent of E. faecium were resistant to ampicillin, 25.5% to vancomycin (VREfm) and 8.8% to teicoplanin.

Conclusion: Significant shifts in the epidemiology and resistance profiles of S. aureus and Enterococcus spp. BSIs in Australian children were observed, making clear the importance of age-stratified reporting in antimicrobial resistance data.