Recombinant ApxIV protein enhances protective efficacy against Actinobacillus pleuropneumoniae in mice and pigs

Examination of the Virulence of Actinobacillus pleuropneumoniae Serovar 16 in Pigs

Different virulence variants of A. pleuropneumoniae are involved in the etiology of porcine pleuropneumonia. The purpose of the present trial was examination of the virulence of the Actinobacillus pleuropneumoniae A-85/14 strain, the type strain of serovar 16, in an animal challenge experiment. Thirty 12-week-old piglets seronegative for A. pleuropneumoniae were allocated into three trial groups each of 10 animals, and they were infected intranasally with 106, 107, or 108 colony forming units (cfu) of the strain, respectively. Clinical signs were recorded twice a day, and the animals were euthanized 6 days after the infection. Typical clinical signs and postmortem lesions of porcine pleuropneumonia were seen in the animals of each trial group; however, they were generally mild, and no significant differences could be seen between the three groups. Even 106 colony forming units of A. pleuropneumoniae A-85/14 strain could induce clinical signs and lesions. Based on these results, the type strain of serovar 16 of A. pleuropneumoniae must be regarded as a typical pathogenic strain of the species.

Swine Gastrointestinal Microbiota and the Effects of Dietary Amino Acids on Its Composition and Metabolism

Many researchers consider gut microbiota (trillions of microorganisms) an endogenous organ of its animal host, which confers a vast genetic diversity in providing the host with essential biological functions. Particularly, the gut microbiota regulates not only gut tissue structure but also gut health and gut functionality. This paper first summarized those common bacterial species (dominated by the Firmicutes, Bacteroidota, and Proteobacteria phyla) in swine gut and then briefly discussed their roles in swine nutrition and health, which include roles in nutrient metabolism, pathogen exclusion, and immunity modulation. Secondly, the current knowledge on how dietary nutrients and feed additives affect the gut bacterial composition and nutrient metabolism in pigs was discussed. Finally, how dietary amino acids affect the relative abundances and metabolism of bacteria in the swine gut was reviewed. Tryptophan supplementation promotes the growth of beneficial bacteria and suppresses pathogens, while arginine metabolism affects nitrogen recycling, impacting gut immune response and health. Glutamate and glutamine supplementations elevate the levels of beneficial bacteria and mitigate pathogenic ones. It was concluded that nutritional strategies to manipulate gut microbial ecosystems are useful measures to optimize gut health and gut functions. For example, providing pigs with nutrients that promote the growth of Lactobacillus and Bifidobacterium can lead to better gut health and growth performance, especially when dietary protein is limited. Further research to establish the mechanistic cause-and-effect relationships between amino acids and the dynamics of gut microbiota will allow swine producers to reap the greatest return on their feed investment.

Comparative Efficacy in Challenge Dose Models of a Toxin Expressing Whole-Cell Vaccine against Eight Serovars of Actinobacillus pleuropneumoniae in Pigs

Actinobacillus pleuropneumoniae is a major economically significant bacterial respiratory pig pathogen, and whole cell vaccines are used to prevent disease. However, there is little data available on multi-serovar whole cell vaccine protection. Therefore, we determined the protective efficacies of a whole-cell A. pleuropneumoniae serovar 1 and 2 vaccine comprising ApxI-III toxins (C-vaccine, Coglapix^®, Ceva, France) against serovars 1, 2, 4, 5, 6, 7, 9/11, and 13. The infection doses used induced disease representative of endemic field conditions, and standard protocols were used for all studies. Protection against homologous serovars 1 and 2 significantly reduced lung lesion scores (LLS) compared to positive controls: p = 0.00007 and p = 0.00124, respectively. The protection against heterologous serovars 4, 5, 6, 7, 9/11, and 13 also significantly reduced LLS: range p = 2.9 × 10^-10 to p = 0.00953. As adjudged by the estimated random effect, reproducibility between studies was high. A highly significant serovar-independent reduction of pathological lung lesions by the C-vaccine was found for all the serovars tested (1, 2, 4, 5, 6, 7, 9/11, and 13). We conclude that the C-vaccine gives high serovar-independent protection against disease and is suitable for this use in the field.

The Association of Bacterin and Recombinant Proteins Induces a Humoral Response in Sheep against Caseous Lymphadenitis

In this study, we investigated the capacity of the recombinant proteins SpaC, NanH, SodC, and PLD of C. pseudotuberculosis to trigger protective humoral and cellular immune responses against experimentally induced C. pseudotuberculosis infection in sheep. The antigens were produced in a heterologous system and were purified by affinity chromatography. Nine sheep were randomly divided into three groups, which were immunized as follows: Group 1 (control)—a mix of adjuvants composed of the inactivated T1 strain of C. pseudotuberculosis and commercial Montanide™ISA 61 VG (T1M); Group 2—rSpaC, rSodC, rPLD, and T1M; Group 3—rNanH, rSodC, rPLD, and T1M. All groups were immunized twice (on days 0 and 30) and challenged on day 90 of the experiment. Humoral and cellular immune responses were evaluated by Enzyme-Linked Immunosorbent Assay (ELISA) to quantify the IgG antibodies and interferon-gamma (IFN-y). Both vaccine formulations with recombinant proteins (groups 2 and 3) could induce a significant humoral IgG immune response in sheep. The proteins rSodC, rPLD, and rNanH were more immunogenic, inducing significant levels of IgG antibodies after the first dose of the vaccine or after the challenge, maintaining constant levels until the end of the experiment. However, it was not possible to differentiate between the cellular responses induced by the vaccines. This lack of effectiveness points toward the need for further studies to improve the efficacy of this subunit-based vaccine approach.

Recombinant suilysin of Streptococcus suis enhances the protective efficacy of an engineered Pasteurella multocida toxin protein

Suilysin (Sly) from Streptococcus suis has been shown to elicit strong immune responses and may act as a vaccine adjuvant. In the present study, we tested the adjuvant effect of Sly using an engineered Pasteurella multocida toxin, rPMT-NC, as the antigen. The antigen was also formulated with other conventional adjuvants (aluminum hydroxide, water-in-oil-in-water) for comparison. The efficacy of these vaccine formulations were evaluated in mice. The optimal dosage of purified rSly for enhancing immune responses in mice was first determined to be 40 μg/ml based on significantly (p < 0.05) increased serum antibody titers, expression of cytokines, including interleukin (IL)-4, IL-12, and interferon (IFN)-γ and the survival rate after challenge with P. multocida. Mice immunized with rPMT-NC + rSly had augmented antibody production and cellular immunity compare to those immunized with rPMT-NC plus other adjuvants. In addition, the survival rate of mice immunized with rPMT-NC + rSly was the highest (70% v.s. 30% of mice immunized with rPMT-NC alone) among all groups. In conclusion, rSly has the potential to be used as a biological adjuvant to enhance immune responses and protective efficacy of protein-based vaccines.

A Combinatorial Vaccine Containing Inactivated Bacterin and Subunits Provides Protection Against Actinobacillus pleuropneumoniae Infection in Mice and Pigs

Actinobacillus pleuropneumoniae (APP) is the etiological agent of porcine contagious pleuropneumonia (PCP) that causes great economic losses in the swine industry. Currently, vaccination is still a commonly used strategy for the prevention of the disease. Commercially available vaccines of this disease, including inactivated bacterins and subunit vaccines, have clinical limitations such as side effects and low cross-protection. In this study, a combinatorial vaccine (Bac-sub) was developed, which contained inactivated bacterial cells of a serovar 1 strain and three recombinant protoxins (rApxIA, rApxIIA, and rApxIIIA). Its side effects, immune protection, and cross-protection were evaluated and compared with a commercial subunit vaccine and a commercial trivalent bacterin in a mouse infection model. The results revealed that the Bac-sub vaccine showed no obvious side effects, and induced higher levels of Apx toxin-specific IgG, IgG1, and IgG2a than the commercial vaccines after booster. After a challenge with virulent strains of serovars 1, 5, and 7, the Bac-sub vaccine provided greater protection (91.76%, 100%, and 100%, respectively) than commercial vaccines. Much lower lung bacterial loads (LBLs) and milder lung lesions were observed in the Bac-sub-vaccinated mice than in those vaccinated with the other two vaccines. The protective efficacy of the Bac-sub vaccine was further evaluated in pigs, which showed that vaccinated pigs displayed significantly milder clinical symptoms and lung lesions than the unvaccinated pigs after the challenge. Taken together, Bac-sub is a safe and effective vaccine that could provide high protection against A. pleuropneumoniae infection in both mice and pigs.

A Multivalent Vaccine Containing Actinobacillus pleuropneumoniae and Mycoplasma hyopneumoniae Antigens Elicits Strong Immune Responses and Promising Protection in Pigs

Actinobacillus pleuropneumoniae (App) and Mycoplasma hyopneumoniae (Mhp) cause porcine pleuropneumonia and mycoplasmal pneumonia, respectively, and have serious impacts on the swine industry because they retard the growth of pigs. To protect pigs against these diseases, we have developed a multivalent vaccine consisting of App bacterins, APP RTX toxins (Apx toxins), and Mhp bacterin and adhesin protein. This vaccine induced the production of higher levels of antibodies against App and Mhp than the commercial vaccine (Nisseiken Swine APM Inactivated Vaccine). Furthermore, the vaccine efficiently protected pigs against virulent App challenge, showing promise as an efficient vaccine for the prevention of two important respiratory diseases, porcine pleuropneumonia and mycoplasmal pneumonia.

Enhancement of Apx Toxin Production in Actinobacillus pleuropneumoniae Serotypes 1, 2, and 5 by Optimizing Culture Condition

Actinobacillus pleuropneumoniae (APP) is a causative agent of porcine pleuropneumonia. Therefore, the development of an effective vaccine for APP is necessary. Here, we optimized the culture medium and conditions to enhance the production yields of Apx toxins in APP serotype 1, 2, and 5 cultures. The use of Mycoplasma Broth Base (PPLO) medium improved both the quantity and quality of the harvested Apx toxins compared with Columbia Broth medium. Calcium chloride (CaCl₂) was first demonstrated as a stimulation factor for the production of Apx toxins in APP serotype 2 cultures. Cultivation of APP serotype 2 in PPLO medium supplemented with 10 μg/ml of nicotinamide adenine dinucleotide (NAD) and 20 mM CaCl₂ yielded the highest levels of Apx toxins. These findings suggest that the optimization of the culture medium and conditions increases the concentration of Apx toxins in the supernatants of APP serotype 1, 2, and 5 cultures and may be applied for the development of vaccines against APP infection.

Recombinant tandem epitope vaccination provides cross protection against Actinobacillus pleuropneumoniae challenge in mice

Actinobacillus pleuropneumoniae (A. pleuropneumoniae/APP) is the pathogen that causes porcine contagious pleuropneumonia. Actinobacillus pleuropneumoniae is divided into 18 serovars, and the cross protection efficacy of epitopes is debatable, which has resulted in the slow development of a vaccine. Consequently, epitope-based vaccines conferring Actinobacillus pleuropneumoniae cross protection have rarely been reported. In this study, B cell epitopes in the head domain of trimeric autotransporter adhesin were predicted, and 6 epitopes were selected. Then, the predicted epitopes (Ba1, Bb5, C1, PH1 and PH2) were connected by linkers to construct a recombinant tandem antigen (rta) gene. The RTA protein encoded by the recombinant rta gene was expressed, and finally the ICR mice were immunized with the RTA protein with or without inactivated Actinobacillus pleuropneumoniae (serovars 1 and 5b) and challenged with Actinobacillus pleuropneumoniae to evaluate the protective effect of the epitope-based vaccine and combined vaccine. The mice in the RTA-immunized group and RTA plus inactivated Actinobacillus pleuropneumoniae vaccine group had a significant improvement in clinical symptoms and a higher level of antibody in the serum than those in the control group. The RTA immune group had a 40% survival rate after Actinobacillus pleuropneumoniae infection, whereas the combination of RTA and inactivated Actinobacillus pleuropneumoniae produced very strong cross immune protection in mice, at least 50% (RTA IB1 + C5) and at most 100% (RTA IB5 + C1), whereas no cross immunoprotection was found in the solo Actinobacillus pleuropneumoniae immune group. Overall, the combination of the RTA protein and inactivated bacteria significantly enhanced the cross protection effects. This implies that RTA protein in combination with a suitable inactivated Actinobacillus pleuropneumoniae strain could be a candidate vaccine for porcine contagious pleuropneumonia.

d- andl-Aspartate regulates growth performance, inflammation and intestinal microbial community in young pigs

Dietary 1%d-Asp andl-Asp affect the growth performance and inflammation in young pigs, which might be associated with gut microbiota.