MexCD-OprJ Multidrug Efflux System of Pseudomonas aeruginosa: Involvement in Chlorhexidine Resistance and Induction by Membrane-Damaging Agents Dependent upon the AlgU Stress Response Sigma Factor

Impact of membrane-active agents on P_mexCD-oprJ-lacZ expression in P. aeruginosa. P. aeruginosa K2899 (K1542::P_mexCD-oprJ-lacZ) (black bars) and AlgU⁻ derivative K2901 (K2897::P_mexCD-oprJ-lacZ) (white bars) were grown to log phase in the presence or absence of CHX, polymyxin B (PXB), ethanol (ETOH), SDS, melittin (MEL), EDTA, n-hexane (HEX), p-xylene (XYL), and the cationic antimicrobial peptides V8 and V681 and assayed for β-galactosidase activity. Values for activity measured were subsequently adjusted for background levels seen for promoter-free, lacZ-containing strains K2900 (K1542::promoterless lacZ) and K2902 (K2897::promoterless lacZ). The results shown are the fold change in activity observed in the presence versus the absence of the indicated agent and are the mean ± the standard deviation of at least two independent experiments performed in triplicate. MDAs were used under the following conditions: CHX, 1/8 MIC (1.25 and 0.16 μg/ml for K2899 and K2901 derivatives, respectively); polymyxin B, 1/4 MIC (0.125 μg/ml); ethanol, 1/8 MIC (0.5% [vol/vol]); SDS, 1/16 MIC (3.1 μg/ml); melittin, 1/4 MIC (15 μg/ml); EDTA, 1/16 MIC (11.6 μg/ml); n-hexane, 1/4 MIC (1.25% [vol/vol]); p-xylene, 1/8 MIC (0.0156% [vol/vol]); antimicrobial peptide V8, 1/8 MIC (8 μg/ml); and antimicrobial peptide V681, 1/8 MIC (16 μg/ml)]. Various MDA concentrations were tested, and results are shown for concentrations that did not adversely impact growth.