1. Microbiology Division; National Institute of Cholera and Enteric Diseases; Kolkata India
2. Department of Bacteriology, Faculty of Medical Sciences; Kyushu University; Fukuoka Fukuoka 812-8582 Japan
3. Seinan Jo Gakuin University; Kitakyushu Fukuoka 803-0835 Japan
4. International Centre for Diarrhoeal Disease and Research; Dhaka Bangladesh