Activity of aztreonam/avibactam and ceftazidime/avibactam against Enterobacterales with carbapenemase-independent carbapenem resistance

Shazad Mushtaq, Anna Vickers, Neil Woodford, David M. Livermore*

*Corresponding author for this work

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Enterobacterales with carbapenemase-independent resistance to carbapenems are sometimes selected during therapy and, on rare occasions, cause outbreaks. Most have extended-spectrum or AmpC β-lactamases, together with changes to permeability or penicillin-binding proteins (PBPs). Newer β-lactam–β-lactamase inhibitor combinations may present useful options for infections due to these organisms. Accordingly, Clinical and Laboratory Standards Institute/European Committee on Antimicrobial Susceptibility Testing broth-microdilution was used to measure the minimum inhibitory concentrations (MICs) of ceftazidime/avibactam and aztreonam/avibactam for 51 carbapenemase-negative Enterobacterales with resistance or reduced susceptibility to carbapenems: genomic sequencing of the least-susceptible organisms was also undertaken. MICs of the two avibactam combinations cross-correlated closely, but with fewer MICs (2/51 vs. 10/51) exceeding 8+4 mg/L in the case of ceftazidime/avibactam. Raised MICs for Escherichia coli were associated with PBP3 inserts together with CMY-42 β-lactamase; correlates among Enterobacter cloacae complex isolates remain elusive, with AmpC and PBP3 sequences found to be species specific. In the case of Klebsiella spp., no MICs exceeding 2 mg/L were seen for either combination. It appears that these avibactam combinations have potential against Enterobacterales with carbapenemase-independent carbapenem resistance or reduced susceptibility, with ceftazidime/avibactam being more reliably active than aztreonam/avibactam.

Original languageEnglish
Article number107081
JournalInternational Journal of Antimicrobial Agents
Issue number3
Publication statusPublished - Mar 2024

Bibliographical note

Publisher Copyright:
© 2023 The Author(s)


  • Aztreonam/avibactam
  • CMY-42 β-lactamase
  • Carbapenem-resistant Enterobacterales
  • Ceftazidime/avibactam
  • Penicillin-binding protein (PBP)3


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