Identification of immunomodulating properties of postbiotics from lactobacilli using the zebrafish (Danio rerio) model.

BACKGROUND & OBJECTIVES: Probiotics are increasingly used in the pet industry to enhance the health and well-being of companion animals. Among them, Lactobacillus strains and their metabolites have demonstrated the ability to maintain immune homeostasis, modulate immune responses, and exhibit antiviral properties. Despite growing interest in postbiotics, non-viable microbial products or metabolic byproducts, scientific literature on their effects remains limited. This study investigates the immunomodulatory and antiviral properties of three postbiotics derived from heat-inactivated Lactobacillus strains using an adult zebrafish (Danio rerio) model challenged with viral hemorrhagic septicemia virus (VHSV). METHODS: A total of 330 zebrafish were assigned to five groups: a non-challenged control (C1), a VHSV-challenged control (C2), and three experimental groups supplemented with one of three heat-treated Lactobacillus strains at the same dosage (Lacticaseibacillus paracasei HA-108; Lactiplantibacillus plantarum HA-119 or Lactobacillus helveticus HA-122). Fish were fed at 4% of biomass for 21 days. Following this period, a subset of the fish was used for immune gene expression profiling and histological examination of the gut and kidney. The remaining fish were challenged with VHSV and monitored for survival over 10 days. RESULTS: All postbiotics treatments modulated immune responses, with L. plantarum HA-119 showing the most pronounced effects, including upregulation of key immune genes such as Il1β and Ifn-γ, indicative of anti-inflammatory and antiviral activity. Histological analysis revealed no significant changes in goblet cell density or villi height, supporting the safety of the postbiotics. Survival rates were significantly higher in the L. plantarum HA-119 and L. helveticus HA-122 groups compared to the VHSV control. CONCLUSIONS: These findings, derived from a well-established zebrafish model, suggest that postbiotics from Lactobacillus strains may enhance antiviral immunity and overall health in vertebrates, supporting their potential as safe, effective microbial-based nutritional interventions in pet nutrition.