Figure 3

CA439-colistin potentiation indirectly affects PmrA/PmrB system activity. Checkerboard assay showing CA439-colistin combination in (a) pmrA mutant or (b) phoP pmrA double mutant. Dark blue regions represent higher cell density. Data represent the mean OD (600 nm) of at least three biological replicates. Right panel shows the CFU counting obtained in each growth condition: DMSO (LB-medium with the addition of DMSO), CA439 (25 μM CA439 alone), colistin (0.156 μg mL⁻¹ colistin alone) and CA439 + colistin (25 μM CA439 + 0.156 μg mL⁻¹ colistin). Fractional inhibitory concentration (FIC) was obtained by dividing the colistin MIC in the presence of CA439 (0.156 μg mL⁻¹) by the colistin MIC in the absence of CA439 (0.625 μg mL⁻¹). Statistical analysis was performed using one-way ANOVA with Tukey’s correction multiple comparison test (**** P < 0.0001; ns, no significant differences).