1. Department of Microbiology; Nagoya City University Medical School; Nagoya Aichi 467-8601 Japan
2. Department of Nutritional Science, Faculty of Health and Welfare Science; Okayama Prefectural University; Soja Okayama 719-1179 Japan
3. Department of Bacterial Infections, Research Institute for Microbial Diseases; Osaka University; Suita Osaka 565-0871 Japan