FIG 5.
Antimicrobial disk diffusion assay in P. aeruginosa efflux pump mutants overexpressing FDH1Cb. Deficient strains in the main RND efflux pumps (ΔmexAB, ΔmexCD, ΔmexEF, and ΔmexXY) expressing FDH1Cb were plated onto LB-agar with or without the inducer IPTG (0.1 mM or 1 mM, as indicated) and challenged with antibiotic-impregnated disks. Cells carrying the empty vector (EV) served as a control, and 10 mM sodium formate were supplemented to the agar plates used for the FDH1Cb strain and the respective vector control. The diameter of the inhibition zone of at least three independent experiments were measured and normalized to the empty vector control as described in Fig. 4. Significant differences between samples were calculated by means of a ratio paired t test and are indicated by asterisks. *, P < 0.05; **, P < 0.01; ***, P < 0.001. LEV, levofloxacin; CIP, ciprofloxacin; NOR, norfloxacin; AMK, amikacin; TOB, tobramycin.