1. Department of Microbiology; University of Würzburg, Biocenter; Am Hubland Würzburg D-97074 Germany
2. Technische Universität München, Chair of Biochemistry; Lichtenbergstr. 4 Garching D-85745 Germany
3. Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Bioanalytical Chemistry; Borstel D-23845 Germany
4. Ludwig Maximilian University of Munich, Max von Pettenkofer-Institute; Pettenkoferstr. 9A München D-80336 Germany