Validation of Aztreonam-Avibactam Susceptibility Testing Using Digitally Dispensed Custom Panels

Aztreonam-avibactam is a combination antimicrobial agent with activity against carbapenemase-producing Enterobacteriaceae (CPE) with metallo-β-lactamases (MβLs). Although aztreonam-avibactam is not yet approved by the U.S. Food and Drug Administration (FDA), clinicians can administer this combination by using two FDA-approved drugs: aztreonam and ceftazidime-avibactam. This combination of drugs is recommended by multiple experts for treatment of serious infections caused by MβL-producing CPE. At present, in vitro antimicrobial susceptibility testing (AST) of aztreonam-avibactam is not commercially available; thus, most clinicians receive no laboratory-based guidance that can support consideration of aztreonam-avibactam for serious CPE infections. Here, we report our internal validation for aztreonam-avibactam AST by reference broth microdilution (BMD) according to Clinical and Laboratory Standards Institute (CLSI) guidelines. The validation was performed using custom frozen reference BMD panels prepared in-house at the Centers for Disease Control and Prevention (CDC). In addition, we took this opportunity to evaluate a new panel-making method using a digital dispenser, the Hewlett Packard (HP) D300e. Our studies demonstrate that the performance characteristics of digitally dispensed panels were equivalent to those of conventionally prepared frozen reference BMD panels for a number of drugs, including aztreonam-avibactam. We found the HP D300e digital dispenser to be easy to use and to provide the capacity to prepare complex drug panels. Our findings will help other clinical and public health laboratories implement susceptibility testing for aztreonam-avibactam.