Membrane integrity evaluation.

To evaluate the bacterial membrane integrity, propidium iodide (PI) uptake was evaluated by flow cytometry using a Cytomics FC 500 instrument (Beckman-Coulter, Inc., Fullerton, CA), as described previously (27, 46). A bacterial mid-log-phase culture diluted to 1 × 10⁶ CFU/ml in MHB was incubated at 37°C for 15 min, 30 min, and 60 min in the presence of 1 μM, 10 μM, or 50 μM peptide and of a final concentration of 10 μg/ml PI. A total of 10⁴ cells were used for each measurement. PI cannot cross an intact bacterial envelope; therefore, the percentage of PI-positive cells indicates the extent of membrane damage.