Figure 5: P. aeruginosa biofilm phenotypes and effectiveness of tobramycin treatment in presence of DMSO 1% or coumarate ester (CE) at 300 µg/mL. (a) After 1 day of incubation, P. aeruginosa fails to form structured confluent aggregate in presence of CE as compared to DMSO treatment. (b) CE considerably increases the susceptibility of P. aeruginosa to tobramycin (100 µg/mL), as shown by the increased proportion of dead cells compared with DMSO. The bacterial viability was assessed by staining the cells with SYTO-9 (green areas—live bacteria) and propidium iodide (red areas—dead bacteria) furnished in the LIVE/DEAD BacLight kit. Cells were visualized using a Leica DM IRE2 inverted fluorescence microscope using a 40x objective lens and colored images were assembled using Adobe Photoshop.