Viability analysis by flow cytometry. Viability was determined by membrane integrity analysis using SYBR Green I (dilution of 5 × 103) and PI (5 μg/mL). Representative pseudo color dot plots with defined gates are shown for (A) P. aeruginosa, (B) B. cepacia and (C) S. aureus in stationary growth phase (t = 12 h) from pure culture. Gates were set manually for each species based on SYBR Green I and PI fluorescence signals of isopropanol-treated (red) and untreated cells (green). For each gate region, relative frequencies of total cells are presented. Only events with positive SYBR Green I fluorescence were considered as cells (see Figure 7).