Annemarie Brauser

• The outer membrane of Gram-negative bacteria and the interaction of different antimicrobial agents were in the focus of this work. It could be shown that classical antibiotics like enrofloxacin as well as different antimicrobial peptides interact with membrane components such as lipopolysaccharides (LPS) as well as with membrane proteins. The outer membrane protein which was investigated in this study was the outer membrane protein F (OmpF). It showed different behaviours if it was reconstituted into membranes depending on the membrane composition and different interactions with various antimicrobial agents. The antimicrobial agents which were used in this work were enrofloxacin, as one example for classical antibiotics (quinolones), and a selection of different antimicrobial peptides including LL20, polymyxin B, hBD-3-l, and poly-Llysine. All of these substances were tested to determine if they showed interactions with LPS and OmpF utilizing several methods. The methods applied were biophysical as well as biological techniques like the Montal-Mueller technique, Foerster resonance energy transfer (FRET) spectroscopy, polarisation measurements, the analysis of the minimal inhibitory concentration, and several others. The results of this study indicate complex interactions of different membrane components of the Gram-negative bacterial outer membrane with different antimicrobial agents. All components and substances influence each other.