1. Department of Microbiology, School of Pharmacy Kitasato University, 5‐9‐1 Shirokane, Minato‐ku Tokyo 108‐8641 Japan
2. Laboratory of Biomolecular Science, School of Veterinary Medicine and Animal Sciences Kitasato University, Higashi 23‐35‐1, Towada Aomori 034‐8628 Japan