Polymyxins induce rapid killing of A. baumannii. A. baumannii cultures were treated with 2 μg of polymyxin B/ml (■) or colistin/ml (⧫) or left untreated (△). At 0, 15, and 30 min, cultures were plated, and the CFU were enumerated. The data are representative of three independent experiments. Points represent the means and bars represent the standard deviation of triplicate samples. ***, P < 0.0001.