2.10. Membrane Permeability Assay

The fluorescent dye propidium iodide (PI) (Beyotime, Shanghai, China) was used to assess the integrity of bacterial cell membranes [30]. MRSA T144 and E. coli B2 cells were incubated with PI (0.5 μM) for 30 min in dark, and the labelled cells were treated with increasing concentrations of WW307. After 1 h incubation, the fluorescence intensity (λexcitation = 535 nm, λemission = 615 nm) was determined using an Infinite M200 Microplate reader (Tecan, Männedorf, Switzerland).