1. Department of Microbiology, Third Military Medical University, Chongqing, P.R. China.
2. Department of Histology and Embryology, Third Military Medical University, Chongqing, P.R. China.
3. Institute of Pathology, Southwest Hospital, Third Military Medical University, Chongqing, P.R. China.
4. Department of Microbiology, School of Basic Medical Sciences, Capital Medical University, Beijing, P.R. China.