Efficacy of recombinant subunit OMP and hly vaccines against Aeromonas hydrophila in Rohu (Labeo rohita)

Differential polyvalent passive immune protection of egg yolk antibodies (IgY) against live and inactivated Vibrio fluvialis in fish

Egg yolk antibodies (IgY) can be prepared in large quantities and economically, and have potential value as polyvalent passive vaccines (against multiple bacteria) in aquaculture. This study prepared live and inactivated Vibrio fluvialis IgY and immunized Carassius auratus prior to infection with V. fluvialis and Aeromonas hydrophila. The results showed that the two IgY antibodies hold effective passive protective rates against V. fluvialis and A. hydrophila in C. auratus. Further, the serum of C. auratus recognized the two bacteria in vitro, with a decrease in the bacteria content of the kidney. The phagocytic activity of C. auratus plasma was enhanced, with a decrease in the expression of inflammatory and antioxidant factors. Pathological sections showed that the kidney, spleen, and intestinal tissue structures were intact, and apoptosis and DNA damage decreased in kidney cells. Moreover, the immunoprotection conferred by the live V. fluvialis IgY was higher than that of the inactivated IgY. Addition, live V. fluvialis immunity induced IgY antibodies against outer membrane proteins of V. fluvialis were more than inactivated V. fluvialis immunity. Furthermore, heterologous immune bacteria will not cause infection, so V. fluvialis can be used to immunize chickens to obtain a large amount of IgY antibody. These findings suggest that the passive immunization effect of live bacterial IgY antibody on fish is significantly better than that of inactivated bacterial antibody, and the live V. fluvialis IgY hold potential value as polyvalent passive vaccines in aquaculture.

Immune response and protective efficacy of Streptococcus agalactiae vaccine coated with chitosan oligosaccharide for different immunization strategy in nile tilapia (Oreochromis niloticus)

In the past decade, the outbreak of Streptococcus agalactiae has caused significant economic losses in tilapia farming. Vaccine immunization methods and strategies have gradually evolved from single-mode to multi-mode overall prevention and control strategies. In this study, an inactivated vaccine of S. agalactiae with a chitosan oligosaccharide (COS) adjuvant was constructed using different administration methods: intraperitoneal injection (Ip), immersion combined with intraperitoneal injection (Im + Ip), immersion combined with oral administration (Im + Or), and oral administration (Or). Safety analysis revealed no adverse effects on tilapia, and the vaccine significantly promoted fish growth and development when administered through Im + Or or Or immunization. Following vaccination, innate immunity parameters including SOD, ACP and CAT activities were all significantly enhanced. Additionally, specific serum IgM antibodies reached their highest level at the 6th week post vaccination. Skin and intestinal mucus IgT antibodies reached peaked at the 6th and 7th week post vaccination, respectively. The relative peak expression values for IL-8, IL-12, MHC-I, MHC-II, IgM, IgT, CD4, CD8, TNFα, IFNγ from Im + Ip group were significantly higher than those in Ip group, Im + Or group and Or group in most cases (p < 0.05). Importantly, the relative protection survival of Im + Ip group was the highest (78.6%), followed by the Ip group (71.4%), the Or group (64.3%) and the Im + Or group (57.1%). In summary, this study encourages further research on multi-channel immunization strategies of other kinds of vaccines in other aquatic economic animals to improve their disease resistance.

Efficacy of a recombinant Lactobacillus plantarum Lp-pPG-Malt as an oral vaccine candidate against Aeromonas hydrophila infection in crucian carp

Aeromonas hydrophila (A. hydrophila), a gram-negative bacterium, causes serious diseases with various clinical symptoms in farm raised fish. Thus, different ways to prevent and control A. hydrophila infection need to be explored, including a vaccine. In this study, we evaluated the protective efficacy of an oral vaccine prepared from the A. hydrophila TPS maltoporin (Malt) with Lactobacillus plantarum (L. plantarum) against A. hydrophila infection in crucian carp (Carassius auratus). For the in vivo experiment, the oral vaccine was administered to crucian carp by feeding them fish diets containing Lp-pPG-Malt, Lp-pPG and PBS for 28 days. The enzyme-linked immunosorbent assay (ELISA), leukocyte phagocytosis assay and real-time quantitative polymerase chain reaction (RT-qPCR) were performed to measure the protective efficacy of the Lp-pPG-Malt. ELISA and leukocyte phagocytosis assay confirmed that Lp-pPG-Malt significantly enhanced the IgM level and nonspecific immune response of crucian carp compared with the control groups (Lp-pPG and PBS). The RT-qPCR results showed that the Lp-pPG-Malt increased the relative expression of immune-related genes (IL-10, IL-1β, TNF-α, IFN-γ) of crucian carp in various tissues (liver, spleen, head kidney and hind intestine). Moreover, Lp-pPG-Malt significantly increased the relative percent survival of fish after intraperitoneal injection with A. hydrophila (55%) compared with the Lp-pPG and PBS groups (0%). These findings suggest that Lp-pPG-Malt can serve as an oral vaccine candidate for A. hydrophila infection and that Malt can be used as an effective antigen in crucian carp farming.