Development of secretory and cell wall anchor recombinant Lactococcus lactis vaccine expressing the porcine enterotoxigenic Escherichia coli K88ac or K99-987P protein

Background: Porcine enterotoxigenic Escherichia coli (ETEC) is one of the primary pathogens causing severe diarrhea in piglets. The main pathogenic factors of this strain are K88ac, K99, and 987P proteins. Methods: The K88ac or K99-987P sequence was used to replace the central part of the AcmA gene, and the cell wall anchor-expressing recombinant pNZ8149-MD/Lactobacillus lactisstrain was constructed. The Usp45 signal peptide, dendritic cell-targeting peptide, and TAT sequence were added to the terminal, and the secretory protein-expressing recombinant pNZ8149-XDT /L.lactis strain was constructed. Mice were immunized with the recombinant strains, and mouse K88, K99, 987P, IgG, sIgA antibodies; IFN-γ; and IL-4 levels were quantified. Results: The experimental group showed increased levels of these immune proteins. sIgA level increased drastically, and the levels of K88, K99, 987P, IgG, and IL-4 also increased significantly. Immunized mice were challenged with a strain of ETEC. The XDT feeding group showed the lowest mortality rate, lower symptom score, lower levels of inflammatory cytokines IL-6 and TNF-α, and milder pathological changes, thus adequately protecting the mice from ETEC infection. Limitations: It remains unclear whether the vaccine can protect pigs from infection with ETEC. Conclusion: The XDT feeding vaccine with K88 or K99-987P antigen was developed.