Antimicrobial Susceptibility Testing of the Combination of Aztreonam and Avibactam in NDM-Producing : A Comparative Evaluation Using the CLSI and EUCAST Methods.

: The combination of aztreonam (ATM) and avibactam (AVI) presents an important therapeutic option for carbapenem-resistant , particularly the NDM-producing . In 2024, both the CLSI and EUCAST published their methods in antimicrobial susceptibility testing for this combination of agents. : Forty carbapenem-resistant isolates, including ( = 35), complex ( = 2), complex ( = 2), and complex ( = 1) were included in this study. All isolates harbored the NDM carbapenemase except one, which had no known detected carbapenemases. Four antimicrobial susceptibility testing methods of the combination of ATM and AVI were evaluated on these isolates, including the CLSI broth disk elution (BDE) method, the disk diffusion (DD) method of aztreonam-avibactam (AZA) following the EUCAST breakpoints, the MIC test strip (MTS) method of AZA following the EUCAST breakpoints, and the gradient strip stacking (SS) method. BDE was used as the standard of comparison. : Using BDE as the standard of comparison, the AZA DD, AZA MTS, and SS methods had 100% categorical agreement (CA), 0% very major error (VME), and 0% major error (ME). The essential agreement (EA) between the AZA MTS and SS method was 57.5%. : The AZA DD, AZA MTS, and the SS methods showed complete concordance with the BDE method. However, the MICs obtained from the AZA MTS and SS were not comparable.