1. Pharmacia and Upjohn AB, Department of Pharmacology, S-751 82, Uppsala, Sweden
2. Department of Animal Physiology, Uppsala University, S-751 24, Uppsala, Sweden
3. Laboratory of Medical Microbial Ecology, Department of Cell and Molecular Biology, Karolinska Institute, S-104 01, Stockholm, Sweden
4. Department of Food Science, Swedish University of Agricultural Sciences, S-750 07, Uppsala, Sweden