[Recombinant yeast-cell microcapsules carrying the DNA vaccine against enterotoxigenic Escherichia coli]

The enterotoxigenic Escherichia coli (ETEC) infection is a major factor restricting the development of animal husbandry. However, the abuse of antibiotics will lead to the antibiotic residues and emergence of antibiotic-resistant bacteria. The existing vaccines face challenges in stimulating intestinal immunity, demonstrating limited prevention effects. Therefore, it is indispensable to develop a new vaccine that is safe and suitable as a feed additive to activate intestinal immunity. This study constructed yeast-cell microcapsules (YCM) carrying the DNA vaccine against ETEC by genetic engineering. Furthermore, animal experiments were carried out to explore the regulatory effects of feeding YCM on the intestinal immune system and intestinal microbiota. Saccharomyces cerevisiae was selected as the oral delivery vehicle (microcapsules) of the DNA vaccine. The codon-optimized nucleic acid sequence of K88, the main antigen of mammal-derived ETEC, was synthesized, and the yeast shuttle vector containing the corresponding DNA vaccine expression cassette was constructed by DNA recombination. The recombinant strain of YCM was prepared by transforming JMY1. Additionally, the characteristics of the YCM strain and its feasibility as an oral vaccine were comprehensively evaluated by the fluorescence reporter assay, gastrointestinal fluid tolerance assay, intestinal epithelial cell adhesion assay, intestinal retention assessment, antiserum detection, and intestinal microbiota detection. The experimental results showed that the DNA vaccine expression cassette was expressed in mammals, and the recombinant strain of YCM could tolerate up to 8 hours of gastrointestinal fluid digestion and had good adhesion to intestinal epithelial cells. The results of mouse feeding experiments indicated that the recombinant strain of YCM could stay in the intestinal tract for at least two weeks, and the DNA vaccine expression cassette carried by YCM entered the intestinal immune system and triggered an immune response to induce the production of specific antibodies. Moreover, feeding YCM recombinant bacteria also improved the abundance of gut microbiota in mice, demonstrating a positive effect in regulating intestinal flora. In summary, we prepared the recombinant strain of YCM carrying the DNA vaccine against ETEC and comprehensively evaluated its characteristics and feasibility as an oral vaccine. Feeding the recombinant YCM could induce specific immune responses and regulate intestinal microbiota. The findings provide a reference for the immunoprevention of ETEC-related animal diseases.