Fig. 2. Mass spectrometry of lipid A extracted from the colistin-susceptible isolates (A) AB001 and (B) AB002 and their colistin-resistant counterpart (C) AB003 with Glu229Asp in pmrB gene. In MALDI-TOF analysis, AB001, AB002, and AB003 isolates all showed two major peaks at 1728 m/z and 1912 m/z, but peaks at 2034 m/z, 2157 m/z, 2261 m/z, and 2384 m/z were detected only in the PDR A. baumannii AB003 isolate. MALDI-TOF, matrix-assisted laser desorption ionization-time of flight; PDR, pan-drug resistant.