Mutations Reducing Susceptibility to Novel LpxC Inhibitors in and Interplay of Efflux and Nonefflux Mechanisms.

Upregulated expression of efflux pumps, target mutations, LpxC protein overexpression, and mutations in were previously shown to mediate single-step resistance to the LpxC inhibitor CHIR-090 in Single-step selection experiments using three recently described LpxC inhibitors (compounds 2, 3, and 4) and mutant characterization showed that these mechanisms affect susceptibility to additional novel LpxC inhibitors. Serial passaging of wild-type and efflux pump-defective strains using the LpxC inhibitor CHIR-090 or compound 1 generated substantial shifts in susceptibility and underscored the interplay of efflux and nonefflux mechanisms. Whole-genome sequencing of CHIR-090 passage mutants identified efflux pump overexpression, mutations, and novel mutations in and in PA4465 as determinants of reduced susceptibility. Two new mutations, encoding A214V and G208S, that reduce susceptibility to certain LpxC inhibitors were identified in these studies, and we show that these and other target mutations differentially affect different LpxC inhibitor scaffolds. Lastly, the combination of target alteration (LpxC) and upregulated expression of LpxC was shown to be tolerated in and could mediate significant decreases in susceptibility.