1. Department of Physiology, University of Veterinary Medicine Hannover, Bischofsholer Damm 15/102, D-30173 Hannover, Germany
2. Institute of Medical Microbiology, University Hospital Münster, D-48149 Münster, Germany
3. ITW, Department of Animal Nutrition, Rheinische Friedrich-Wilhelms-University Bonn, D-53113 Bonn, Germany