Our hypothesis is that cells in Gram-negative bacterial biofilms are more resistant to antimicrobial agents than planktonic cells because they are also better in coping with, and/or avoiding exposure to, oxidative stress than planktonic cells. We believe that strategies to deal with this oxidative stress are essential for the survival of treated biofilm cells. Using state-of-the-art molecular tools we will dissect the response of selected microorganisms to the stress imposed by treatment-induced ROS production.