Figure 2

CA439 enhancement of the bactericidal effect of colistin is partially PhoP/PhoQ-dependent. Checkerboard assay showing CA439-colistin combination in (a) phoP mutant, (b) phoQ mutant and (c) phoPQ 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 (0.312 μg mL⁻¹ colistin alone) and CA439 + colistin (25 μM CA439 + 0.312 μg mL⁻¹ colistin). Fractional inhibitory concentration (FIC) was obtained by dividing the colistin MIC in the presence of CA439 (0.312 μg mL⁻¹) by the colistin MIC in the absence of CA439 (1.25 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).