Time-kill experiments displaying the activity of imipenem-relebactam alone and in combination with amikacin or colistin against P. aeruginosa isolates with imipenem-relebactam MICs of 1/4 μg/ml and 2/4 μg/ml. I/R, imipenem-relebactam; AMK, amikacin; CST, colistin; *, synergy with I/R plus AMK; ǂ, synergy with I/R plus CST.