Trends of β-Lactamase Occurrence AmongEscherichia coliandKlebsiella pneumoniaein United States Hospitals During a 5-Year Period and Activity of Antimicrobial Agents Against Isolates Stratified by β-Lactamase Type

Background The temporal and longitudinal trends of β-lactamases and their associated susceptibility patterns were analyzed for Escherichia coli and Klebsiella pneumoniae isolates consecutively collected in 56 United States hospitals during 2016–2020. Methods Isolates (n = 19 453) were susceptibility tested by reference broth microdilution methods. Isolates that displayed minimum inhibitory concentration (MIC) values ≥2 mg/L for at least 2 of the following compounds—ceftazidime, ceftriaxone, aztreonam, or cefepime—or resistance to the carbapenems were submitted to whole genome sequencing for identification of β-lactamases. Longitudinal and temporal trends were determined by slope coefficient. New CTX-M and OXA-1 variants were characterized. Results Extended-spectrum β-lactamases (ESBLs) were detected among 88.0% of the isolates that displayed elevated cephalosporin/aztreonam MICs without carbapenem resistance. blaCTX-M-15 was detected among 55.5% of the ESBL producers. ESBL rates were stable over time, but significant increases were noted among bloodstream infection and K pneumoniae isolates, mainly driven by an increase in blaCTX-M. Carbapenem resistance and carbapenemase genes were noted among 166 and 145 isolates, respectively, including 137 blaKPC, 6 blaSME, 3 blaOXA-48–like, and 3 blaNDM. Ceftazidime-avibactam and carbapenems were very active (>99% susceptibility) against ESBL producers without carbapenem resistance. Ceftazidime-avibactam inhibited 97.0% of the carbapenem-resistant isolates. This agent and meropenem-vaborbactam inhibited 96.4% and 85.0% of the 2020 isolates, respectively. Conclusions Overall, ESBL-producing isolates were stable, but an increase was noted for K pneumoniae isolates driven by CTX-M production. Carbapenem-resistant Enterobacterales rates decreased in the study period. The prevalence of metallo-β-lactamases and OXA-48–like remains low. Continuous surveillance of β-lactamase–producing isolates is prudent.