Assessment of Ceftazidime-Avibactam 30/20-μg Disk, Etest versus Broth Microdilution Results When Tested against Enterobacterales Clinical Isolates

The objective of this research was to evaluate the correlation between inhibitory zones and MIC when testing ceftazidime-avibactam using disk diffusion, Etest, and broth microdilution method established by the Clinical and Laboratory Standards Institute (CLSI). Four-hundred and 58 isolates of Enterobacterales isolated from 54 medical centers from the China Antimicrobial Surveillance Network (CHINET) in 2016 to 2020 were collected. Antimicrobial susceptibility testing using broth microdilution, Etest, and disk diffusion were performed according to the CLSI. Of the 458 Enterobacterales, 172% (79/458) and 82.8%(379/458) were resistant or susceptible to ceftazidime-avibactam by broth microdilution, respectively. Compared with the broth microdilution method, the categorical agreement (CA) and essential agreement (EA) of the Etest were 99.6% (456/458) and 94.8% (434/458), respectively; the major error (ME) and very major error (VME) were both 0.2% (1/458). For disk diffusion, the CA and VME were 99.8% (457/458) and 0.2% (1/458), respectively. For Escherichia coil, the CA and EA of the Etest were 100% and 97.1% (135/ 139), respectively. The CA of the disk diffusion was 100%. For Klebsiella pneumoniae, the CA and EA of the Etest were 993% (288/290) and 93.4% (271/290), respectively, the ME and VME were both 03% (1/290). The CA and VME of disk diffusion were 99.7% (289/290) and 03% (1/290), respectively. For other Enterobacterales, the CA and EA of the Etest were 100% and 96.6% (28/29), respectively. The CA of the disk diffusion was 100%. Ceftazidime-avibactam disk diffusion (30/20-tig disks) and Etest demonstrated good performance for ceftazidime-avibactam susceptibility testing against Enterobacterales clinical isolates. IMPORTANCE Multidrug-resistant Gram-negative bacteria, especially for extended-spectrum beta-lactamases-producing and carbapenemase-producing Enterobacterales, are disseminating rapidly around the world. Treatment options for these infections are limited, which prompt the development of novel or combinational therapies to combat the infections caused by multidrug-resistant pathogens. The newly available beta-lactam combination agent ceftazidime-avibactam has been demonstrated good in vitro and in vivo activity against ESBL, AmpC, KPC-2, or OXA-48-like-producing isolates and has shown promise in treating carbapenem-resistant Enterobacterales infections. Concerningly, there are few available automated systems for ceftazidime-avibactam susceptibility testing, and the broth microdilution method is hard to perform in most routine laboratories. Therefore, we urgently need an economical and practical method for the accurate detection of ceftazidime-avibactam activity against Gram-negative bacilli. Here, we evaluate the performance of the disk diffusion and Etest compared with the reference broth microdilution method against Enterobacterales clinical strains.