Fig. 1.

Total fractional inhibitory concentrations (ΣFIC) of meropenem and ertapenem for carbapenem-resistant Gram-negative bacteria (CR-GNB). ΣFIC in each box was calculated by adding the value of the horizontal axis (FIC of meropenem) and that of the longitudinal axis (FIC of ertapenem). The color of each box and the number in each box represent the total count of the isolates with the corresponding ΣFIC. The area below the red line represents isolates that performed complete or partial synergy (ΣFIC＜1) in the checkerboard synergy testing. The area above the red line represents isolates that exhibited antagonism (ΣFIC = 2, top-left box) and additivity (1 ≤ ΣFIC < 2, the remaining boxes).