FIG 1.

MgrB-dependent colistin resistance provides enhanced survival against CAMP. K. pneumoniae survival against lysozyme (A) and colistin (B). (A) Mid-log-phase (OD₆₀₀) cultures of WT, MgrB⁺, and MgrB⁻ were resuspended in PBS and incubated with the appropriate concentrations of lysozyme for 1 hour at 37°C. Shown is the mean and SEM of three independent assays (in duplicate). (B) Mid-log-phase (OD₆₀₀) cultures of each strain were diluted to ∼10⁵ CFU/mL in LB before being incubated with increasing concentrations of colistin for 30 minutes at 37°C. Shown is the mean and SEM of three independent assays (in duplicate). (C to E) Fatty acid composition was conducted using GC-FID via the fatty acid methyl ester (FAME) derivatization from a bacterial culture pellet. Strains were analyzed for lipid A analysis via FLAT with 3 biological replicates for WT (C), MgrB⁻ (D), and MgrB+ (E). (F) Fatty acid composition of lipid A of each strain. Statistical differences were calculated using Kruskal-Wallis tests with Dunn’s test of multiple comparisons within each concentration group (A and B) or fatty acid group (F). There was no significant difference between the WT and MgrB⁺ strains. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; n.s., not significant.