1. Department of Child and Maternal Health Care; School of Public Health, Anhui Medical University; Hefei, Anhui 230032, P.R. China
2. Department of Microbiology; Anhui Medical University; Hefei, Anhui 230032, P.R. China
3. School of Life Science; University of Science and Technology of China; Hefei, Anhui 230027, P.R. China