An Attenuated Escherichia coli K88ac LT(S63K) Δ STb Efficiently Provides Protection Against Enterotoxigenic Escherichia coli in the Mouse Model

To develop an attenuated vaccine candidate against K88ac enterotoxigenic (ETEC), a novel ( ) K88ac Δ with mutation and deletion was generated using site mutagenesis and λ-Red homologous recombination based on wild paternal ETEC strain C83902. K88ac Δ showed very similar fimbriae expression and growth kinetics to the wild strain C83902, but it was significantly attenuated according to the results of a rabbit ligated ileal loop assay and mouse infection study. Oral inoculation with K88ac Δ stimulated the mucosa immune response and induced the secretion of IgA to K88ac in the intestines in mice. A challenge experiment revealed that the attenuated strain provided efficient protection against C83902 in the following 7 days and at the 24th day post-inoculation, suggesting that the attenuated isolate could act as an ecological protectant and vaccine in preventing K88ac ETEC.