1. Graduate School of Medicine; Dentistry and Pharmaceutical Sciences; Okayama University; 1-1-1, Tsushima-Naka Kita-Ku Okayama 700-8530 Japan
2. Collaborative Research Center of Okayama University for Infectious Diseases in India; National Institute of Cholera and Enteric Diseases; 57 Dr. S. C. Banerjee Road, ID Hospital Campus, Beliaghata Kolkata West Bengal 700010 India