The Ins and Outs of Susceptibility Testing for New β-Lactam/β-Lactamase Inhibitor Combinations for Gram-Negative Organisms.

Ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam are among the newest β-lactam/β-lactamase inhibitors (BL/BLIs) introduced to the North American antibiotic market. All have broad Gram-negative activity, including against certain carbapenemases. Despite this, susceptibility testing is warranted due to variable activity against certain β-lactamases (e.g., oxacillinases) and the presence of acquired resistance mechanisms in some isolates. Here, we discuss what we know about these new antimicrobial agents and how to navigate implementation of susceptibility testing and reporting of these agents in clinical laboratories.