Targeting Lipopolysaccharide Transport Induces Membrane Lipid Remodeling and Sensitizes Acinetobacter baumannii to Colistin Treatment

Acinetobacter baumannii is an opportunistic pathogen with increasing resistance to conventional antibiotics, necessitating novel antimicrobial strategies. The outer membrane integrity of most Gram-negative bacteria critically depends on the lipopolysaccharide (LPS) transport (Lpt) system, which mediates LPS translocation from the inner to the outer membrane. In this study, we perform a structure-based virtual screen against the Lpt system of Acinetobacter and identify a somatostatin octapeptide analogue (termed C4) as a candidate hit. Notably, C4 demonstrates modest antibacterial activity but exhibits robust synergistic activity with colistin. Integrated lipidomic and transcriptomic analyses reveal that C4 treatment induces membrane lipid remodeling, particularly a selective accumulation of phosphatidylglycerol (PG), which was associated with enhanced colistin activity. Moreover, C4 exposure significantly upregulates mlaC expression, a key determinant of phospholipid retrograde transport. Deletion of mlaC reduces C4-induced PG enrichment and abolishes C4-mediated potentiation of colistin, whereas mlaC overexpression enhances this potentiation and complementation partially restores it. In murine pneumonia and thigh infection models, the C4-colistin combination significantly reduces bacterial burden and inflammatory cytokine levels, and attenuates histopathological damage. Our findings highlight the anti-infective potential of targeting the Lpt system through membrane lipid remodeling and underscore C4 as a promising colistin adjuvant for combating A. baumannii infections.