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

Abstract

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.

Keywords: Biofilm based oral vaccine; Growth performance; Gut associated lymphoid tissues; Haemato-biochemical indices; Polyclonal antibody; Striped catfish.

Fig. 1

A: Free cells of A. hydrophila from the one day cultured broth (100X); B: Microphotograph of the 4-day old biofilm cell of A. hydrophila, note that the fingerlike projections (red arrow) of the glycocalyx (100X) C: FE-SEM of 4-day old biofilm cell of A. hydrophila. Note that the clumps of bacterial cell (circle) (15000X) D: Computer blown up image of biofilm of A. hydrophila showing the A. hydrophila inside the glycocalyx matrix (arrow).

Fig. 2

Relative percent survival of P. hypophthalmus upon challenge with A. hydrophila

Fig. 3

SDS – PAGE (A) and western blot (B) analysis of the purified pangasius immunoglobulin (Ig): Lane 1: Molecular weight marker Lane 2: Affinity purified serum, Lane 3: Whole serum of pangasius, Lane 4 and 5: western blots showing reactivity of the PAb to the heavy chain of the purified Ig.

Fig. 4

ELISA antibody titer in P. hypophthalmus orally vaccinated with BF and FC of A. hydrophila.

Fig. 5

Comparison of SGPT (IU/l) between treatment groups.

Fig. 6

Comparison of SGOT (IU/l) between treatment groups. Same letters indicate no significant differences (P>0.05) between groups (Mean ± SE, n = 9).

Fig. 7

Comparison of alkaline phosphate (IU/l)) between treatment groups.

Fig. 8

Comparison of cholesterol (mg/dl) between treatment groups.

Fig. 9

Comparison of triglycerides (mg/dl) between treatment groups. Same letters indicate no significant differences (P > 0.05) between groups (Mean ± SE, n = 9).

Fig. 10

Comparison of glucose (mg/dl) between treatment groups. Different letters indicate significant differences (P < 0.05) between groups (Mean ± SE, n = 9).

Fig. 11

Histomorphological analysis of mid gut of P. hypophthalmus fed vaccinated and unvaccinated diets. A: Transvers section of BF vaccinated fishes showing two focal aggregations of lymphoid tissue (GALT) in lamina propria B: Gut histology of FC vaccinated fishes showing less aggregation of lymphoid cells near the lamina propria (red arrow) and C: Unvaccinated fishes showing no aggregation of lymphoid tissue (GALT) in either lamina propria or mucosal tissues (arrows) as compared with BF and FC group fishes.