Effect of microencapsulated Fiber2-displaying probiotics loaded with inulin nanoparticles on immunity against fowl adenovirus serotype 4 in chickens

In this study, phthalate inulin nanoparticles (PINs) were chemically modified and characterized. The internalization of PINs into the probiotic E. faecalis, which delivering Fiber2 protein of fowl adenovirus serotype 4 (FAdV-4), was investigated. The expression of the Fiber2 protein in E. faecalis was detected using western blot analysis. To protect recombinant E. faecalis from degradation of in the gastric acid environment, sodium alginate was used to encapsulate the bacteria. The survival ratio and release of E. faecalis in simulated gastrointestinal fluid was assessed. Oral administration of microencapsulated E. faecalis loaded with PINs (Micro-E/Fiber2-PINs) or inulin (Micro-E/Fiber2-inulin) was conducted, followed by an experimental challenge with FAdV-4 in chickens to evaluate immune responses and protection. The results showed the internalization of PINs into the bacteria promoted bacteria growth, and significantly improved the expression level of Fiber2. After incubation in simulated gastric fluid, the number of viable bacteria from the Micro-E/Fiber2-PINs group was significantly higher than that from the E. faecalis/Fiber2 group. The release of bacteria from the microcapsules was completed within 30 min. Animal experiments demonstrated that oral immunization with Micro-E/Fiber2-PINs significantly enhanced humoral and cellular immune responses, relieved inflammatory injury in FAdV-targeted organs, and improved survival rate of challenged chickens. This study presents promising potential for developing oral vaccines against pathogen infection.