Minimum inhibitory concentrations of aztreonam–avibactam, ceftazidime–avibactam and meropenem in clinical isolates of Klebsiella pneumoniae harboring carbapenemase genes

This study was aimed at understanding the distributions of the MICs (minimum inhibitory concentrations) of aztreonam–avibactam, ceftazidime–avibactam and meropenem with respect to Klebsiella pneumoniae isolates producing different types of carbapenemases and their combinations. K. pneumoniae isolates were collected between 2019 and 2022 from 37 hospitals. PCR was used to screen for bla_KPC-, bla_NDM- and bla_OXA-48-like genes. MICs were determined by the broth microdilution method for meropenem, aztreonam–avibactam and ceftazidime–avibactam at a constant avibactam concentration of 4 mg l⁻¹. MIC distributions were analyzed for groups of isolates based on the identified carbapenemases including their combinations. The AZT/AVI MIC₅₀ and MIC₉₀ for all NDM-positive isolates were 0.25 and 0.5, respectively, and for serine-carbapenemase-only producers, they were 0.25 and 1 mg l⁻¹, respectively. The CZD/AVI MIC₅₀ and MIC₉₀ values for serine-carbapenemase-only producers were 1 and 4 mg l⁻¹, respectively. The AZT/AVI MIC₅₀ and MIC₉₀ values for co-producers and single carbapenemase producers were the same (i.e., 0.25 and 1 mg l⁻¹, respectively). The total proportion of meropenem-susceptible isolates (≤8 mg l⁻¹) among all the carbapenemase producers was 25.1% (31.1% among single-carbapenemase producers and 9.2% among co-producers). The results support the use of aztreonam–avibactam for the empirical treatment of infections caused by any carbapenemase producers.