1. 1 Department of Microbiology, University of Dhaka, Dhaka, Bangladesh
2. 2 Department of Biology, University of Bergen, Bergen, Norway
3. 3 Present address: Department of Microbiology, Jagannath University, 9-10 Chittaranjan Road, Dhaka 1100, Bangladesh
4. 4 Present address: International Centre for Diarrheal Disease Research, Bangladesh (icddr,b), GPO Box 128, Dhaka 1000, Bangladesh
5. 5 Present address: Department of Immunology, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba-city, Chiba 260-8670, Japan
6. 6 Present address: Microbiology Program, Department of Mathematics and Natural Sciences, BRAC University, 66 Mohakhali, Dhaka 1212, Bangladesh