The bacterial strain used in this study (Enterotoxigenic E. coli
K88 C83907) was purchased from the China Institute of Veterinary
Drugs Control (Beijing, China) and preserved by the National Engineering
Laboratory of Bio-feed Safety and Pollution Prevention
(Hangzhou, China). The challenge strain harbored the genes for
enterotoxin STb, LT and the genes for fimbria F4ac detected as
described