1. Department of Chemical Technology, Institute of Biomedical Technology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands; Laboratory of General Biochemistry and Physical Pharmacy, Department of Pharmaceutics, University of Ghent, Harelbekestraat 72, 9000 Ghent, Belgium; and Department of Medical Microbiology, AMC, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands