Changing Epidemiology of Carbapenemases Among Carbapenem-Resistant Enterobacterales From United States Hospitals and the Activity of Aztreonam-Avibactam Against Contemporary Enterobacterales (2019–2021)

Abstract

As the frequency of metallo-β-lactamase (MBL)–producing Enterobacterales is increasing worldwide, effective antimicrobials to treat the infections caused by these organisms are urgently needed. The activity of aztreonam-avibactam and comparators were evaluated against 27,834 Enterobacterales isolates collected from 74 US medical centers in 2019–2021. Isolates were susceptibility tested by broth microdilution. An aztreonam-avibactam pharmacokinetic/pharmacodynamic breakpoint of ≤8 mg/L was applied for comparison. Antimicrobial susceptibility and the frequency of key resistance phenotypes were assessed then stratified by year and infection type. Carbapenem-resistant Enterobacterales (CRE) were screened for carbapenemase (CPE) genes by whole genome sequencing (WGS). Aztreonam-avibactam inhibited >99.9% of Enterobacterales at ≤8 mg/L. Only 3 isolates (0.01%) had an aztreonam-avibactam MIC >8 mg/L. CRE rates were 0.8%, 0.9%, and 1.1% in 2019, 2020, and 2021, respectively; 99.6% (260/261) of CRE isolates were inhibited at an aztreonam-avibactam MIC of ≤8 mg/L. CRE susceptibility to meropenem-vaborbactam decreased from 91.7% in 2019 to 83.1% in 2020 and 76.5% in 2021 (82.1% overall). CRE, multidrug-resistant, and extensively drug-resistant phenotypes were markedly higher among isolates from pneumonia compared to other infections. The most common carbapenemase among CRE was KPC (65.5% of CRE), followed by NDM (11.1%), OXA-48–like (4.6%), SME (2.3%), and IMP (1.5%). Among non-CPE–producing CRE isolates (n=44; 16.9% of CRE), 97.7% were inhibited at ≤8 mg/L of aztreonam-avibactam and 85.4% were meropenem-vaborbactam susceptible. The frequencies of MBL and OXA-48 type producers increased markedly. Aztreonam-avibactam demonstrated potent and consistent activity against Enterobacterales across infection types and over time.