Checkerboard MIC and Effect Model analysis
The β-lactamase genotype of each bacterial strain and the MIC values of aztreonam/nacubactam alone and nacubactam MIC in the presence of 4 mg L-1 of aztreonam for each bacterial strain are shown in Table 1. Fig. 2 shows the dose-response relationship of aztreonam MIC to nacubactam concentration for each strain analysed by the Inhibitory Effect Sigmoid I max Model. All strains were resistant to aztreonam alone, but the combination of aztreonam and nacubactam decreased MIC in a nacubactam concentration-dependent manner. Interestingly, nacubactam alone also showed slight antibacterial activity against all bacterial strains.