OmpR (TCS response regulator) of Aeromonas veronii plays a major role in drug resistance, stress resistance and virulence by regulating biofilm formation.

Aeromonas veronii (A. veronii), a highly pathogenic bacteria with a wide range of hosts, widely exists in the environment of humans, animals and aquatic animals, and can cause a variety of diseases. In this study, the receptor regulator ompR in the envZ/ompR of two-component system was selected to construct a mutant strain (Δ ompR) and a complement strain (C-ompR) to explore the regulatory effect of ompR on the biological characteristics and virulence of TH0426. The results showed that the ability of biofilm formation and osmotic stress of TH0426 were significantly reduced (P < 0.001), the resistance to ceftriaxone and neomycin were slightly down-regulate when the ompR gene was deleted. At the same time, animal pathogenicity experiments showed that the virulence of TH0426 was significantly down-regulated (P < 0.001). These results indicated that ompR gene regulates the biofilm formation of TH0426, and regulates some biological characteristics of TH0426, including drug sensitivity, resistance to osmotic stress, and also affects its virulence.

Mineralization Reduces the Toxicity and Improves Stability and Protective Immune Response Induced by Toxoplasma gondii.

Vaccination is an ideal strategy for the control and prevention of toxoplasmosis. However, the thermostability and effectiveness of vaccines limit their application. Here, calcium mineralization was used to fabricate Toxoplasma gondii tachyzoites as immunogenic core-shell particles with improved immune response and thermostability. In the current study, T. gondii RH particles coated with mineralized shells were fabricated by calcium mineralization. The mineralized shells could maintain the T. gondii tachyzoites structural integrity for at least 12 months and weaken the virulence. Immunization of mice with mineralized tachyzoites induced high levels of T. gondii-specific antibodies and cytokines. The immunized mice were protected with a 100% survival rate in acute and chronic infection, and brain cyst burdens were significantly reduced. This study reported for the first time the strategy of calcium mineralization on T. gondii and proved that mineralized tachyzoites could play an immune protective role, thus expanding the application of biomineralization in T. gondii vaccine delivery.

Functional analysis of ascP in Aeromonas veronii TH0426 reveals a key role in the regulation of virulence.

Aeromonas veronii is a pathogen which can induce diseases in humans, animals and aquatic organisms, but its pathogenic mechanism and virulence factors are still elusive. In this study, we successfully constructed a mutant strain (ΔascP) by homologous recombination. The results showed that the deletion of the ascP gene significantly down-regulated the expression of associated effector proteins in A. veronii compared to its wild type. The adhesive and invasive abilities of ΔascP to EPC cells were 0.82-fold lower in contrast to the wild strain. The toxicity of ΔascP to cells was decreased by about 2.91-fold (1 h) and 1.74-fold (2 h). Furthermore, the LD50 of the mutant strain of crucian carp was reduced by 19.94-fold, and the virulence was considerably attenuated. In contrast to the wild strain, the ΔascP content in the liver and spleen was considerably lower. The titers of serum cytokines (IL-8, TNF-α, and IL-1ß) in crucian carp after the infection of the ΔascP strain were considerably lower in contrast to the wild strain. Hence, the ascP gene is essential for the etiopathogenesis of A. veronii TH0426.

The effects of dietary supplementation of ginseng stem and leaf saponins on the antioxidant capacity, immune response, and disease resistance of crucian carp, Carassius auratus.

This is the first study to explore the positive effects of ginseng stem and leaf saponins (GSLS) on antioxidant capability, immunity, and disease resistance of crucian carp. Seven hundred fifty crucian carps (initial body weight: 25 ± 0.15 g (mean ± SE)) were randomly allocated into five groups with three replicates each; five diets supplemented with the final concentration of 0, 1, 2, 4, and 8 g/kg GSLS were fed to crucian carp for 5 weeks. The results demonstrated that, at a concentration of 8 g/kg, the contents of IgM, C4, SOD, GSH-Px, and the activity of AKP in serum of crucian carp gradually increased at 7, 14, 21, 28, and 35 days, and the expression of immune-relative cytokine genes (TNF-α, IL-10, IFN-γ) in the liver, spleen, and the intestinal tract also had a significant up-regulation (P < 0.05), and which were significant difference compared with control (P < 0.05). The above results demonstrated that dietary GSLS showed enhancement effects on the antioxidant and anti-inflammatory capability, and innate immune response of crucian carp. The feed of 8 g/kg GSLS for 1 week could improve the survival rate 44% more than the control group when crucian carp infected Aeromonas hydrophila (A. hydrophila). In conclusion, the addition of GSLS at a concentration of 8 g/kg in the diet improve immune-related enzyme activity better, immune-relative cytokine expression, and disease resistance.

Oral vaccination with recombinant Lactobacillus casei expressing Aeromonas hydrophila Aha1 against A. hydrophila infections in common carps.

The immunogenicity of Aha1, an OMP of Aeromonas hydrophila mediating the adhesion of bacteria onto the mucosal surface of hosts has been established. In this study, recombinant vectors, pPG1 and pPG2, carrying a 1366 bp DNA fragment that was responsible for encoding the 49 kDa Aha1 from A. hydrophila were constructed, respectively, then electroporated into a probiotic strain Lactobacillus casei CC16 separately to generate two types of recombinants, L. casei-pPG1-Aha1 (Lc-pPG1-Aha1) and L. casei-pPG2-Aha1 (Lc-pPG2-Aha1). Subsequently, these were orally administered into common carps to examine their immunogenicity. The expression and localization of the expressed Aha1 protein relative to the carrier L. casei was validated via Western blotting, flow cytometry, and immune fluorescence separately. The recombinant vaccines produced were shown high efficacies, stimulated higher level of antibodies and AKP, ACP, SOD, LZM, C3, C4 in serum in hosts. Immune-related gene expressions of cytokines including IL-10, IL-1ß, TNF-α, IFN-γ in the livers, spleens, HK, and intestines were up-regulated significantly. Besides, a more potent phagocytosis response was observed in immunized fish, and higher survival rates were presented in common carps immunized with Lc-pPG1-Aha1 (60%) and Lc-pPG2-Aha1 (50%) after re-infection with virulent strain A. hydrophila. Moreover, the recombinant L. casei were shown a stronger propensity for survivability in the intestine in immunized fish. Taken together, the recombinant L. casei strains might be promising candidates for oral vaccination against A. hydrophila infections in common carps.