Fig 6.

Effect of phosphoethanolamine and galactosamine modifications on colistin and polymyxin B resistance in A. baumannii. (A) Resistance to colistin and polymyxin B was evaluated for ATCC 19606 and CM012S (PmrB P233S-activating mutant strain) strains following the disruption of various LOS modification genes (pmrC, eptA, naxD), and in CM012S strain following the disruption of pmrA. The strains were cultured to reach a steady state, washed with PBS, and prepared in PBS to achieve an OD₆₀₀ of 0.2. Subsequently, a 10-fold serial dilution (from 10⁻¹ to 10⁻⁵) of the bacterial suspension was prepared. This diluted suspension was then plated onto LB agar medium containing 10 µg/mL colistin and 10 µg/mL polymyxin B, which was incubated for 24 h at 37°C. Experiments were performed independently in triplicate, and representative agar plates are shown. (B) Lipid A was extracted from each strain, and MALDI-TOF/MS was used to analyze its structure. The predicted structures of lipid A and their corresponding peak mass-to-charge ratios are displayed at the top.