Performance of disk diffusion method for aztreonam in combination with avibactam against Enterobacteriales

Abstract Objectives To evaluate the performance of an in-house developed disk diffusion method for aztreonam in combination with avibactam against Enterobacteriales. Methods The in vitro antibacterial activity of aztreonam with avibactam against 204 carbapenemase-producing Enterobacteriales was determined by a disk diffusion method, with a broth microdilution method as a reference. Results The optimal S/R breakpoints for disk diffusion tests of 30/20 and 10/4 µg disks, calculated by the dBETs software using the model-based approaches, were ≥22/≤21 and ≥12/≤11 mm, respectively. On the basis of the estimated breakpoints, the CAs for disk diffusion tests of 30/20 and 10/4 µg aztreonam/avibactam disks were both 98.0%, with 0.5% major error and 37.5% very major error. Conclusions The home-made disk diffusion method is an economical and practical method for clinical microbiology laboratories to determine the antibacterial susceptibility of aztreonam with avibactam against Enterobacteriales.