1. Department of Gastroenterology; Juntendo University School of Medicine; Bunkyo-ku, Tokyo Japan
2. Animal Research Center; Sapporo Medical University School of Medicine; Chuo-ku, Sapporo Japan
3. Center of Excellence for Infection Control Science; Graduate School of Medicine, Juntendo University; Bunkyo-ku, Tokyo Japan
4. Department of Microbiology; Juntendo University School of Medicine; Bunkyo-ku, Tokyo Japan
5. Department of Gastroenterology; Juntendo University Urayasu Hospital; Urayasu-city, Chiba Japan