Efficacy of bi-valent whole cell inactivated bacterial vaccine against Motile Aeromonas Septicemia (MAS) in cultured catfishes (Heteropneustes fossilis, Clarias batrachus and pangasius pangasius) in Bangladesh

Evaluating the effectiveness of an autogenous vaccine to prevent motile Aeromonas septicaemia in striped catfish (Pangasianodon hypophthalmus) formulated by using DNA fingerprints for bacterial inclusion

Many Aeromonas species are infecting striped catfish in the Mekong Delta in Vietnam. This study aimed to evaluate the effectiveness of autogenous vaccines developed by analysing the genetic diversity through DNA fingerprint analysis. A total of 38 Aeromonas strains isolated from 2017 to 2022 were analysed for phenotypic differences using the repetitive element sequence PCR (rep-PCR) with the (GTG)5 single-primer. The vaccines were water-in-oil emulsion whole-cell inactivated with two monovalent vaccines containing antigens of Aeromonas VH31 (VC-VH31), or Aeromonas VH74 (VC-VH74) and a bivalent vaccine with both Aeromonas VH31 and VH74 (VC-VH31/74). The experiment lasted for 60 days in water at 28 °C and was performed in triplicates. Blood samples were taken at 0, 15, 30, 45 and 60 day post vaccination (dpv) to collect the serum. The challenge infection was performed as a co-infection immersion challenge of two homologous strains of Aeromonas VH31 and Aeromonas VH74 at dose LD60 value 0,55 × 107 cfu/mL and 0,47 × 108 cfu/mL, respectively. The highest relative percent of survival (RPS) of the VC-VH31/74 bivalent vaccine was 100 % and the fish displayed no clinical signs of disease. At 30 dpv, the concentration of total leukocytes, lymphocytes, monocytes and granulocytes was highest in the group receiving the dual vaccine. Additionally, the results showed that the difference between the vaccines was significant when ELISA analysis of IgM-specific antibodies in serum, and the result was highest in VC-VH31/74 bivalent vaccine after 30 days (p < 0.05) and remained stable until 60 dpv. The vaccine showed good immunogenicity and high protective efficacy against Aeromonas spp. in catfish. Thereby demonstrating the potential of Aeromonas autogenous vaccine use.

Evaluation of feed utilization, immune response and disease resistance in striped catfish, Pangasianodon hypophthalmus (Sauvage 1878) fed with a novel Aeromonas hydrophila biofilm vaccine

Striped catfish, Pangasianodon hypophthalmus was immunized with Biofilm (BF) and Free cell (FC) of Aeromonas hydrophila vaccine at 1010 CFU g-1 for 20 days and monitored for growth parameters, immune responses and disease resistance up to 60 day post vaccination (dpv). Pangasius catfish in the BF vaccinated group had considerably higher growth and feed utilization than the FC vaccinated and unvaccinated groups (p < 0.05). Biofilm vaccinated group showed a significant increase (p < 0.05) in the mean weight gain (46.91 ± 0.59) than the FC (35.94 ± 0.21) and unvaccinated group (34.92 ± 0.35). The vaccinated fishes were challenged with A. hydrophila at 107 CFU/ml. Significant higher relative percentage survival (RPS) was recorded with BF (84.21 ± 1.49%) compared to that with FC (33.33 ± 1.21%). Polyclonal antibody-based ELISA was used to quantify the antibody titre. BF vaccinated group showed significantly higher antibody titer compared to other treatments (p < 0.05). Moreover, higher haematological parameters recorded in the present study were differentially stimulated by the oral administration of A. hydrophila biofilm vaccine. The mean total protein, albumin, and globulin levels of the BF vaccine groups were significantly higher (p < 0.05) than the mean total protein, albumin, and globulin contents of the unvaccinated group. Furthermore, biochemical stress parameters (SGPT, SGOT) in the vaccinated groups showed an incremental trend in the early days of the experimental period. However, the values were significantly lower (p < 0.05) in the biofilm group on 20 dpv onwards indicating improved health condition. Vaccinated BF fishes showed gut associated lymphoid tissues (GALT) within the laminar propria of mid gut. But in FC group fishes showed less aggregation of lymphoid cells. The unvaccinated control fish had no lymphoid cell aggregation in their intestines. The findings of the current research suggested that biofilm vaccine has the capability to be one of the potential oral vaccines in striped catfish against A. hydrophila infection.