Cytoplasmic membrane depolarization (DiSC3-5) assay.

Suspensions of P. aeruginosa ATCC 9027 cells grown overnight were harvested, resuspended in 5 mM HEPES buffer at pH 7.4, and adjusted to an OD₆₀₀ of 0.2. The cytoplasmic membrane potential-sensitive probe DiSC₃-5 (Sigma-Aldrich, MO, USA) was added to the inoculum to a final concentration of 10 μM, and the mixture was incubated at room temperature for 1 h. The suspension was transferred into a 10-mm stirring quartz cuvette, and 1 μl of each polymer in different concentrations was added after a stable signal was detected. The fluorescence intensity at excitation and emission wavelengths of 622 nm and 670 nm, respectively, was monitored until a plateau was reached by using a Quanta Master spectrophotometer (Photon Technology International, NJ, USA) with a slit width of 0.5 nm. The fluorescence intensity values after the addition of Triton X (0.1%, wt/vol) was taken as maximum depolarization, and the percentage of depolarization was calculated.