A Simple Disk Stacking Plus Micro-Elution Method for Rapid Detection of the Synergistic Effect of Aztreonam and Ceftazidime/Avibactam Against Metallo-beta-Lactamase Producing Enterobacterales

Purpose: To establish and evaluate a simple disk stacking plus micro-elution (DSE) method that can be routinely performed to rapidly detect the synergistic effect between aztreonam (ATM) and ceftazidime/avibactam (CZA) against metallo-ss-lactamase (MBL)-producing carbapenem-resistant Enterobacterales (CRE). Methods: The DSE method was established, and a total of 32 MBL-producing CRE isolates collected from multiple centers were tested for ATM-CZA synergy. The results obtained after 8 h of incubation were compared with those obtained by a reference checkerboard assay (CBA) after 18 similar to 24 h. Reproducibility experiments were completed on three separate days. Results: The reproducibility study showed that the results of the DSE method were precise. Compared with CBA, the DSE method exhibited excellent performance, with 92.8% sensitivity, 100.0% specificity 93.8% categorical agreement, 0.0% very major error, 0.0% major error, and 6.2% minor error over three days of testing. Conclusion: The DSE method is a simple, rapid and practical method for ATM-CZA combination testing. Further evaluation should be completed to improve its clinical application.