Introduction: The use of probiotics in order to increase the immunogenicity and efficiency of vaccines in aquatic animals has been widely used in the last decade. In this research, the effect of Bacillus subtilis probiotic on the immunogenicity of the bivalent oral vaccine of Streptococcus iniae, Streptococcus agalactiae encapsulated with alginate/chitosan in the Nile tilapia fish (Oreochromis niloticus) was measured and in terms of immunogenicity, its effects on growth indicators and blood parameters were compared.
Materials & methods: First, the bivalent bacterium Streptococcus agalactia and Streptococcus agalactiae were successfully encapsulated by the internal emulsification method. Then 600 pieces of Nile tilapia fish weighing 30±2.32 gr were divided into 10 groups (Each group in three repetitions of 20 numbers) include A: treatment group with S. iniae, B: treatment group with S. agalactiae, C: treatment group with bivalent vaccine, D: treatment group with S. iniae and Bacillus subtilis, E: treatment group with S. agalactiae and Bacillus subtilis, F: immunized with bivalent vaccine and Bacillus subtilis, G: immunized with encapsulated S. iniae and Bacillus subtilis, H: immunized with encapsulated S. agalactiae and Bacillus subtilis, I: treatment group with bivalent encapsulated vaccine and Bacillus subtilis, and Control. The fish were fed and kept under the same conditions for two months, and on days 0, 30 and 60, along with fish biometry, samples were taken from each treatment and blood and serum were isolated. Growth indices and some immune and blood indices of fish were compared between treatments. Then, the fish of each group were challenged with live bacteria Streptococcus agalactiae and Streptococcus iniae, and the deaths of the treatments were recorded up to 14 days and compared between the treatments.
Results: The results showed that the growth indices were affected by immunization and the growth indices including food conversion coefficient, specific growth coefficient and percentage of weight gain in the treatment group with bivalent encapsulated vaccine and Bacillus subtilis were improved significantly compared to the control treatment (p>0.05). Among the Immune indicators, anti-streptococcus agalactiae and anti-streptococcus iniae antibody levels, NBT recovery rate, serum globulin and protein levels, and serum lysozyme activity were significantly improved in the sampling stages in the oral treatment of encapsulated and Bacillus subtilis (p>0.05). Blood parameters including: hemoglobin, hematocrit and white blood cells showed a significant difference between research treatments (p>0.05). Investigations showed that in both stages of sampling on the 30th and 60th days, the highest number of white blood cells was related to the encapsulated and Bacillus subtilis treatments (p>0.05). The lowest rate of deaths in the challenge with live bacteria S. agalactiae and S. iniae, with 36.7% and 30%, respectively, was related to the treatment group with bivalent encapsulated vaccine and Bacillus subtilis, compared to the control treatment (100%) showed a significant decrease (p>0.05).
Conclusion: Therefore, it can be concluded that according to the favorable results of Bacillus subtilis probiotic immunogenicity on bivalent encapsulated vaccine in the current research and the special advantages of oral vaccine administration, with additional research it is possible to use this method as an alternative to injectable vaccine. |
