Work

Probiotic Lactobacillus acidophilus provides an adjuvant effect to an orally administered chitosan nanoparticle-based Salmonella subunit vaccine in broilers against Salmonella Enteritidis infection

Year: 2026

Type: article

Abstract: Salmonella enterica serovar Enteritidis (SE) is a prominent zoonotic pathogen that contaminates poultry meat and eggs, leading to widespread foodborne illness in humans. Despite better biosecurity measures and available commercial vaccines, SE foodborne illness from broiler meat remains a challenge, necessitating a novel vaccination strategy. This study investigated the adjuvant efficacy of probiotic Lactobacillus acidophilus to a mannose-conjugated chitosan nanoparticle-based Salmonella subunit nanovaccine encapsulated with outer membrane proteins (OMP) and flagella antigens (FLA) of SE. Broiler chicks ( n = 17–22 birds/group across six treatment groups) were administered the probiotic in ovo (embryonic day 18) and post-hatch (days 2, 4, and 6), and oral vaccination was performed at days 3 and 21 and challenged with SE at day 35. The physical nature of the nanovaccine includes zeta potential (34.62 ± 1.34 mV), particle size (286.5 ± 6.87 nm), and polydispersity index (0.45 ± 0.04), ensuring stability and suitability for mucosal delivery. Our results demonstrated that the probiotic-nanovaccine combination synergistically elicited specific immune responses associated with a 1.2 log 10 reduction in cecal SE colonization at day post challenge 4 compared with a commercial live-attenuated vaccine. Immunological analysis revealed an elevated frequency of activated B-cells, increased specific secretory IgA in the intestines and bile. Cytokine profiling in the cecal tonsils showed upregulation of Th1/Th17-associated cytokines (IFN-γ/IL-17) gene expression and transition to regulatory cytokine IL-10, indicative of a balanced immune response. Furthermore, 16S rRNA sequencing of cecal contents showed that the probiotic-nanovaccine did not alter overall microbiota diversity but significantly shifted microbial community composition ( R 2 = 0.378, p = 0.001). Probiotic-supplemented groups were enriched with short-chain fatty acid producing Clostridiales , including Blautia, Butyricicoccus , and Christensenellaceae R-7 group , whereas the commercial vaccine group exhibited higher abundance of Escherichia/Shigella and reduced Lactobacillus . These findings underscore the potent adjuvant effect of L. acidophilus in enhancing the immunogenicity and protective efficacy of an oral Salmonella nanovaccine, while favorably modulating the gut microbiome. This integrated probiotic-nanovaccine approach represents a promising, antibiotic-free paradigm for mitigating salmonellosis in poultry, with implications for reducing zoonotic transmission, incidence of foodborne illness, and antimicrobial resistance.

Source: Frontiers in Microbiology

DOI: 10.3389/fmicb.2026.1898587