Immunogenicity of a Salmonella Enteritidis mutant as vaccine candidate and its protective efficacy against salmonellosis in chickens

Assessment of environmental safety and protective efficacy of O-antigen deficient DIVA capable Salmonella Enteritidis against chicken salmonellosis

In this study, we incorporated deletion of the O-antigen ligase gene to an attenuated Salmonella Enteritidis (SE) strain, JOL919 (SE PS; Δlon ΔcpxR), using the Lambda-Red recombination method and evaluated the safety and immunological aspects of the novel genotype, JOL2381 (SE VS: Δlon, ΔcpxR, ΔrfaL). Assessment of fecal shedding and organ persistence following administration via oral and IM routes revealed that the SE VS was safer than its parent strain, SE PS. Immunological assays confirmed that immunization via the oral route with SE PS was superior to the SE VS. However, chickens immunized with SE PS and SE VS strains via the IM route showed higher humoral and cell-mediated immune responses. Compared to PBS control, the IM route of immunization with SE VS resulted in a higher IgY antibody titer and expansion of CD4+ and CD8+ T-cell populations, which resulted in the clearance of Salmonella from the liver and splenic tissues. Furthermore, deletion of the O-antigen ligase gene caused lower production of LPS-specific antibodies in the host, promoting DIVA functionality and making it a plausible candidate for field utilization. Due to significant protection, high attenuation, and environmental safety concerns, the present SE VS strain is an ideal choice to prevent chicken salmonellosis and ensure public health.

Vaccines to Control Salmonella in Poultry

This review is focused on describing and analyzing means by which Salmonella enterica serotype strains have been genetically modified with the purpose of developing safe, efficacious vaccines to present Salmonella-induced disease in poultry and to prevent Salmonella colonization of poultry to reduce transmission through the food chain in and on eggs and poultry meat. Emphasis is on use of recently developed means to generate defined deletion mutations to eliminate genetic sequences conferring antimicrobial resistance or residual elements that might lead to genetic instability. Problems associated with prior means to develop vaccines are discussed with presentation of various means by which these problems have been lessened, if not eliminated. Practical considerations are also discussed in hope of facilitating means to move lab-proven successful vaccination procedures and vaccine candidates to the marketplace to benefit the poultry industry.

Natural Evolution of Porcine Epidemic Diarrhea Viruses Isolated from Maternally Immunized Piglets

The porcine epidemic diarrhea virus (PEDV) can cause severe piglet diarrhea or death in some herds. Genetic recombination and mutation facilitate the continuous evolution of the virus (PEDV), posing a great challenge for the prevention and control of porcine epidemic diarrhea (PED). Disease materials of piglets with PEDV vaccination failure in some areas of Shanxi, Henan and Hebei provinces of China were collected and examined to understand the prevalence and evolutionary characteristics of PEDV in these areas. Forty-seven suspicious disease materials from different litters on different farms were tested by multiplex PCR and screened by hematoxylin-eosin staining and immunohistochemistry. PEDV showed a positivity rate of 42.6%, infecting the small and large intestine and mesenteric lymph node tissues. The isolated strains infected Vero, PK-15 and Marc-145 multihost cells and exhibited low viral titers in all three cell types, as indicated by their growth kinetic curves. Possible putative recombination events in the isolates were identified by RDP4.0 software. Sequencing and phylogenetic analysis showed that compared with the classical vaccine strain, PEDV SX6 contains new insertion and mutations in the S region and belongs to genotype GIIa. Meanwhile, ORF3 has the complete amino acid sequence with aa80 mutated wild strains, compared to vaccine strains CV777, AJ1102, AJ1102-R and LW/L. These results will contribute to the development of new PEDV vaccines based on prevalent wild strains for the prevention and control of PED in China.

Co-infection of Salmonella enteritidis with H9N2 avian influenza virus in chickens

Salmonella and avian influenza virus are important pathogens affecting the poultry industry and human health worldwide. In this experimental study, we evaluated the consequences of co-infection of Salmonella enteritidis (SE) with H9N2 avian influenza virus (H9N2-AIV) in chickens. Four groups were included: control group, H9N2-AIV group, H9N2-AIV + SE group, and SE group. Infected chickens were intranasally inoculated with H9N2-AIV at 21 days of age and then orally administered SE on the same day. The birds were monitored for clinical signs, mortality rates, and alterations in body weight. Sera, intestinal fluids, oropharyngeal, and cloacal swabs, and tissue samples were collected at 2, 6, 10, and 14 days post-infection (dpi). Significant increases in clinical signs and mortality rates were observed in the H9N2-AIV + SE group. Moreover, chickens with co-infection showed a significant change in body weight. SE faecal shedding and organ colonization were significantly higher in the H9N2-AIV + SE group than in the SE group. H9N2-AIV infection compromised the systemic and mucosal immunity against SE, as evidenced by a significant decrease in lymphoid organ indices as well as systemic antibody and intestinal immunoglobulin A (IgA) responses to SE and a significant increase in splenic and bursal lesion scores. Moreover, SE infection significantly increased shedding titres and duration of H9N2-AIV. In conclusion, this is the first report of co-infection of SE with H9N2-AIV in chickens, which leads to increased pathogenicity, SE faecal shedding and organ colonization, and H9N2-AIV shedding titre and duration, resulting in substantial economic losses and environmental contamination, ultimately leading to increased zoonoses.

Recombinant-attenuated Salmonella Pullorum strain expressing the hemagglutinin-neuraminidase protein of Newcastle disease virus (NDV) protects chickens against NDV and Salmonella Pullorum challenge

Newcastle disease virus (NDV) and Salmonella Pullorum have significant damaging effects on the poultry industry, but no previous vaccine can protect poultry effectively. In this study, a recombinant-attenuated S. Pullorum strain secreting the NDV hemagglutinin-neuraminidase (HN) protein, C79-13ΔcrpΔasd (pYA-HN), was constructed by using the suicide plasmid pREasd-mediated bacteria homologous recombination method to form a new bivalent vaccine candidate against Newcastle disease (ND) and S. Pullorum disease (PD). The effect of this vaccine candidate was compared with those of the NDV LaSota and C79-13ΔcrpΔasd (pYA) strains. The serum hemagglutination inhibition antibody titers, serum immunoglobulin G (IgG) antibodies, secretory IgA, and stimulation index in lymphocyte proliferation were increased significantly more (p < 0.01) in chickens inoculated with C79-13ΔcrpΔasd (pYA-HN) than with C79-13ΔcrpΔasd (pYA) but were not significantly increased compared with the chickens immunized with the LaSota live vaccine (p > 0.05). Moreover, the novel strain provides 60% and 80% protective efficacy against the NDV virulent strain F48E9 and the S. Pullorum virulent strain C79-13. In summary, in this study, a recombinant-attenuated S. Pullorum strain secreting NDV HN protein was constructed. The generation of the S. Pullorum C79-13ΔcrpΔasd (pYA-HN) strain provides a foundation for the development of an effective living-vector double vaccine against ND and PD.

Oral vaccination with a live Salmonella Enteritidis/Typhimurium bivalent vaccine in layers induces cross-protection against caecal and internal organ colonization by a Salmonella Infantis strain

Salmonella is an important zoonotic agent, and poultry products remain one of the main sources of infection for humans. Salmonella Infantis is an emerging serotype in poultry worldwide, reflected by an increased prevalence in poultry flocks, on broiler meat and in human foodborne illness cases. In the current study, the efficacy of oral administration of a live monovalent Salmonella Enteritidis and a live bivalent Salmonella Enteritidis/Typhimurium vaccine, against a Salmonella Enteritidis and Infantis infection, was determined. Oral administration of the live vaccines to day-old chickens caused a decrease in caecal colonization by Salmonella Enteritidis, but not Infantis, at day 7, when challenged at day 2. Vaccination with the bivalent vaccine at day 1 resulted in a decreased spleen colonization by both Salmonella Infantis and Enteritidis. Twice (at day 1 and week 6) and thrice vaccination (at day 1, week 6 and 16) of laying hens with the bivalent vaccine resulted in a decreased caecal colonization by Salmonella Enteritidis and Infantis, and significantly lower oviduct colonization levels by Salmonella Enteritidis. These data show cross-protection against Salmonella Infantis by oral administration of live vaccine strains belonging to other serogroups.

Efficacy of genogroup 1 based porcine epidemic diarrhea live vaccine against genogroup 2 field strain in Japan

Background

Porcine epidemic diarrhea (PED) is a lethal infectious disease in suckling piglets with symptoms including watery diarrhea caused by PED virus (PEDV). Since the late 1990’s, live vaccines based on genogroup 1 virus have been used in Japan, and a significant amount of the vaccine has been used even after new genogroups invaded in 2013. In this study, we evaluated the effect of a conventional PED live vaccine on a newly prevalent genogroup 2 field strain in experimental and field situations.

Methods

Two pregnant sows were administered twice the live vaccine before farrowing. A pregnant sow was served as a negative control. All newborn piglets were challenged with the genogroup 2 virus, and clinical signs were monitored for 7 days post challenge. PEDV-specific immune responses in serum and milk of the sows were assayed by virus neutralization assay. The efficacy of PED live vaccine in vaccinated or non-vaccinated farms was evaluated by comparing the mortality rate of suckling piglets after the onset of PED.

Results

The challenged piglets exhibited watery diarrhea with or without vaccination. However, the clinical score of piglets born from vaccinated sows significantly improved after the 4th day of the challenge. The survival rate of piglets in the vaccinated group at the end of the experimental period was 80%, whereas in the control group was 0%. Neutralizing antibody titers in serum and milk of control sow was negative throughout the experimental period, whereas high titers were observed in the vaccinated sows. The vaccinated farms significantly reduced the mortality rate of suckling piglets after the onset of PED, compared to farms not vaccinated.

Conclusions

The conventional PED live vaccine induced the lactogenic immunity to vaccinated sows and showed partial protection against the genogroup 2 virus both under the experimental and field conditions.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-0940-8) contains supplementary material, which is available to authorized users.

Killing of Serratia marcescens biofilms with chloramphenicol

Serratia marcescens is a Gram-negative bacterium with proven resistance to multiple antibiotics and causative of catheter-associated infections. Bacterial colonization of catheters mainly involves the formation of biofilm. The objectives of this study were to explore the susceptibility of S. marcescens biofilms to high doses of common antibiotics and non-antimicrobial agents. Biofilms formed by a clinical isolate of S. marcescens were treated with ceftriaxone, kanamycin, gentamicin, and chloramphenicol at doses corresponding to 10, 100 and 1000 times their planktonic minimum inhibitory concentration. In addition, biofilms were also treated with chemical compounds such as polysorbate-80 and ursolic acid. S. marcescens demonstrated susceptibility to ceftriaxone, kanamycin, gentamicin, and chloramphenicol in its planktonic form, however, only chloramphenicol reduced both biofilm biomass and biofilm viability. Polysorbate-80 and ursolic acid had minimal to no effect on either planktonic and biofilm grown S. marcescens. Our results suggest that supratherapeutic doses of chloramphenicol can be used effectively against established S. marcescens biofilms.

Vaccination efficacy with marrow mesenchymal stem cell against cancer was enhanced under simulated microgravity

Stem cell vaccination can induce consistent and strong anti-tumor immunity against cancer in mice model. The antigenic similarity between tumors and embryos has been appreciated for many years and reflects the expression of embryonic gene products by cancer cells and/or cancer-initiating stem cells. Taking advantage of this similarity, we have tested a prophylactic lung cancer vaccine composed of allogeneic murine MSCs. Based on this conception, we first compared their tumor vaccines intervention effects of adult MSCs and MSCs under simulated microgravity (MSC/SMG). In this study, BALB/c mice were vaccinated with MSCs or MSC/SMG, compared with mice vaccinated with phosphate buffered saline (PBS) as negative controls. We then subcutaneously implanted the A549 human lung cancer cell line into vaccinated mice and monitored tumor growth potential in vivo. The smaller tumor size and less tumor weight were observed in mice vaccinated with MSCs or MSC/SMG, compared with that of the Control group. Particularly, it was much more significant in the group of MSC/SMG than that group of the MSCs. Vaccination with SMG treated MSCs inhibited proliferation and promoted apoptosis of tumor tissue. SMG/MSC vaccination induced bothTh1-mediated cytokine response; CD8-dependent cytotoxic response which reduced the proportion of Treg cells. Furthermore, SMG/MSC vaccination significantly increased MHC1 and HSPs proteins expression. In conclusion, we demonstrated the SMG could improve tumor-suppressive activity of MSC. The enhanced anti-tumor immune response of MSCs/SMG was strongly associated with the higher expression of MHC class I molecule on DCs, and the abundance of HSPs in the SMG treated MSCs may make antigens in the MSC more cross-presentable to the host DCs for generating protective antitumor activity. This study gains an insight into the mechanism of MSCs anti-tumor efficacy and gives a new strategy for cancer therapies in the future.

A live attenuated mutant of Salmonella Montevideo triggers IL-6, IFN-γ and IL-12 cytokines that co-related with humoral and cellular immune responses required for reduction of challenge bacterial load in experimental chickens

A live attenuated Salmonella enterica serovar Montevideo (SM) mutant JOL1599 was constructed by deletion of virulence-associated genes. The protective efficacy and immune response profiles of chickens immunized with JOL1599 were investigated. Immunized chickens demonstrated significant increases in plasma IgG and lymphocyte proliferative responses (P≤0.05). Increased levels of IL-6, INF-γ, and IL-12 were also observed. Immunized birds strongly responded to infection by rapid stimulation of a CD4+ subset of T cells. Organ bacterial recovery assay revealed a significant reduction in the challenge strain among immunized birds. Multiple doses of JOL1599 enhanced the immune responses of the birds as revealed by ascending trends of the immunological profiles. These findings indicate that immunization of chickens with JOL1599 may provide protection against Salmonella Montevideo infection via induction of IL-6, INF-γ, and IL-12 protective cytokines, which in turn triggers conducive humoral and cell-mediated immune responses.

Protective efficacy and immune responses by homologous prime-booster immunizations of a novel inactivated Salmonella Gallinarum vaccine candidate

Purpose

Salmonella enterica serovar Gallinarum (SG) ghost vaccine candidate was recently constructed. In this study, we evaluated various prime-boost vaccination strategies using the candidate strain to optimize immunity and protection efficacy against fowl typhoid.

Materials and Methods

The chickens were divided into five groups designated as group A (non-immunized control), group B (orally primed and boosted), group C (primed orally and boosted intramuscularly), group D (primed and boosted intramuscularly), and group E (primed intramuscularly and boosted orally). The chickens were primed with the SG ghost at 7 days of age and were subsequently boosted at the fifth week of age. Post-immunization, the plasma IgG and intestinal secretory IgA (sIgA) levels, and the SG antigen-specific lymphocyte stimulation were monitored at weekly interval and the birds were subsequently challenged with a virulent SG strain at the third week post-second immunization.

Results

Chickens in group D showed an optimized protection with significantly increased plasma IgG, sIgA, and lymphocyte stimulation response compared to all groups. The presence of CD4⁺ and CD8⁺ T cells and monocyte/macrophage (M/M) in the spleen, and splenic expression of cytokines such as interferon γ (IFN-γ) and interleukin 6 (IL-6) in the immunized chickens were investigated. The prime immunization induced significantly higher splenic M/M population and mRNA levels of IFN-γ whereas the booster showed increases of splenic CD4⁺ and CD8⁺ T-cell population and IL-6 cytokine in mRNA levels.

Conclusion

Our results indicate that the prime immunization with the SG ghost vaccine induced Th1 type immune response and the booster elicited both Th1- and Th2-related immune responses.

A live attenuated Salmonella Enteritidis secreting detoxified heat labile toxin enhances mucosal immunity and confers protection against wild-type challenge in chickens

A live attenuated Salmonella Enteritidis (SE) capable of constitutively secreting detoxified double mutant Escherichia coli heat labile toxin (dmLT) was developed. The biologically adjuvanted strain was generated via transformation of a highly immunogenic SE JOL1087 with a plasmid encoding dmLT gene cassette; the resultant strain was designated JOL1641. A balanced-lethal host-vector system stably maintained the plasmid via auxotrophic host complementation with a plasmid encoded aspartate semialdehyde dehydrogenase (asd) gene. Characterization by western blot assay revealed the dmLT subunit proteins in culture supernatants of JOL1641. For the investigation of adjuvanticity and protective efficacy, chickens were immunized via oral or intramuscular routes with PBS, JOL1087 and JOL1641. Birds immunized with JOL1641 showed significant (P ≤ 0.05) increases in intestinal SIgA production at the 1^st and 2^nd weeks post-immunization via oral and intramuscular routes, respectively. Interestingly, while both strains showed significant splenic protection via intramuscular immunization, JOL1641 outperformed JOL1087 upon oral immunization. Oral immunization of birds with JOL1641 significantly reduced splenic bacterial counts. The reduction in bacterial counts may be correlated with an adjuvant effect of dmLT that increases SIgA secretion in the intestines of immunized birds. The inclusion of detoxified dmLT in the strain did not cause adverse reactions to birds, nor did it extend the period of bacterial fecal shedding. In conclusion, we report here that dmLT could be biologically incorporated in the secretion system of a live attenuated Salmonella-based vaccine, and that this construction is safe and could enhance mucosal immunity, and protect immunized birds against wild-type challenge.

CXC chemokine CXCL12 tissue expression and circulating levels in peptic ulcer patients with Helicobacter pylori infection

Helicobacter pylori (H. pylori) infection is among the most prevalent human infections. CXCL12 is a well-known CXC chemokine involved in inflammation and play major roles in angiogenesis. There is currently very limited data on the role of CXCL12 in peptic ulcer disease. Hence, we aimed to explore whether CXCL12 is involved in the pathogenesis of peptic ulcer induced by H. pylori. In this study, we enrolled 102 H. pylori-infected patients, including 51 with active ulcer (GA) and 51 with healing ulcer (GH). We also recruited 50 healthy subjects as control, which did not show any sign or symptoms of chronic inflammatory diseases, infection, or immune-related disorders. Endoscopy was performed to determine the stage of the disease. ELISA was used for detection of H. pylori infection and CXCL12 measurement. We also employed western blotting to detect CXCL12 in ulcerative lesions of H. pylori. Demographic data were also collected by questionnaire. Our results demonstrated that CXCL12 serum levels in GA group (151.8±18.31pg/mL) were significantly higher than those in GH (36.89±6.78pg/mL) and control groups (33.77±9.12pg/mL) (P<0.0001). However, we did not observe a significant difference between GH and control groups. Moreover, overexpression of CXCL12 in gastric lesions of patients in GA group was confirmed by Western blot analysis. According to the result of the present study, it could be concluded that CXCL12 is involved in the pathogenesis and healing of H. pylori-induced peptic ulcer. CXCL12 serum levels may also be used to distinguish between GA and GH phases of the disease.

Salmonella enterica serovar Typhimurium utilizes the ClpPX and Lon proteases for optimal fitness in the ceca of chickens

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a leading cause of salmonellosis. Poultry and poultry products are implicated in transmission of Salmonella to humans. In 2013, an outbreak of S Typhimurium occurred that comprised 39 states within the United States and was associated with backyard flocks of chickens. Colonization of the avian host by S Typhimurium requires numerous genetic factors encoded within the bacterium. Of particular interest are genetic factors induced by alternative sigma factors within S Typhimurium since these genetic elements are important for adaptation to different environmental stresses. The heat shock response is a dedicated change in gene regulation within bacteria in response to several stresses, specifically growth at 42°C. Because chickens have a higher body temperature than other animals (42°C) the hypothesis was tested that components of the heat shock response are important for optimal fitness within the chicken. To this end, deletion of the heat shock proteases clpPX (BTNC0022) or lon (BTNC0021) was accomplished and the bacterial fitness in vivo was compared to the "wild-type" strain (NC1040) using a competition assay. One-day-old chicks were orally gavaged with an equal mixture of NC1040 and either BTNC0022 or BTNC0021. Quantification of viable bacteria over time by using plate counts indicated that deletion of either heat shock protease resulted in significantly reduced colonization of the chicken ceca compared to the wild-type strain. To satisfy the molecular Koch's postulates, clpPX and lon mutants were complemented in trans using a low-copy number plasmid for additional in vivo experiments. Complementation studies confirmed the importance of either heat shock protease to colonization of the chicken ceca. This report demonstrated that both ClpPX and Lon were important for optimal fitness within chickens. Moreover, these results suggested that components of the heat shock may be critical factors used by S. Typhimurium for colonization of poultry. The use of feed additives or other treatments that inactivate or inhibit ClpPX or Lon may reduce the bacterial burden of S. Typhimurium in poultry.

Yeast β-d-glucans induced antimicrobial peptide expressions against Salmonella infection in broiler chickens

The present study was designed to investigate the effects of yeast β-d-glucans (YG) on gene expression of endogenous β-defensins (AvBDs), cathelicidins (Cath) and liver-expressed antimicrobial peptide-2 (LEAP-2) in broilers challenged with Salmonella enteritidis (SE). 240 day-old Cobb male broilers were randomly assigned to 2×2 factorial arrangements of treatments with two levels of dietary YG (0 or 200mg/kg in diet) and two levels of SE challenge (0 or 1×10(9) SE at 7-9 days of age). The results showed SE infection reduced growth performance,and increased salmonella cecal colonization and internal organs invasion, increased concentration of intestinal specific IgA and serum specific IgG antibody, as compared to uninfected birds. SE challenge differentially regulated AvBDs, Caths and LEAP-2 gene expression in the jejunum and spleen of broiler chickens during the infection period. However, YG supplementation inhibited the growth depression by SE challenge, and further increased level of serum specific IgG and intestinal specific IgA antibody. Higher level of salmonella colonization and internal organs invasion in the SE-infected birds were reduced by YG. SE-induced differentially expression patterns of AMPs genes was inhibited or changed by YG. Results indicated YG enhance chicken's resistance to salmonella infection.

Utilization of a Modified Phage E Protein Lysis System Accounts for Increased Biomass in Salmonella Gallinarum Ghosts

A major limiting issue of bacterial ghost technology involves the stable maintenance of Phix174 lysis gene E expression. Unwanted leaky expression of gene E in the absence of induction temperature results in reduced biomass production of host bacterium, consequently leading to the lower yield of bacterial ghost. To mitigate the leaky expression status of lysis gene E, we utilized a novel E-lysis system in which gene E is located between sense λpR promoter with a CI857 regulator and antisense ParaBAD promoter with the AraC regulator. In the presence of L-arabinose at 28 C, unwanted transcription of lysis gene E from λpR promoter is repressed by a simultaneous transcription event from ParaBAD promoter by means of anti-sense RNA-mediated inhibition. Tight repression of lysis gene E in the absence of induction temperature resulted in higher bacterial cell number in culture suspension and, consequently, higher production of Salmonella Gallinarum (SG) ghost biomass. The safety and protective efficacy of the SG ghost vaccine were further examined in chickens. All of the immunized chickens showed significantly higher mucosal and systemic antibody responses accompanied by a potent antigen-specific lymphocyte proliferative response. Vaccination of chickens with SG ghost preparation offered efficient protection against wild-type SG challenge.

Inhibition of Salmonella-induced apoptosis as a marker of the protective efficacy of virulence gene-deleted live attenuated vaccine

Vaccination is one of the best protection strategies against Salmonella infection in humans and chickens. Salmonella bacteria must induce apoptosis prior to initiating infection, pathogenesis and evasion of host immune responses. In this study, we evaluated the efficacy of vaccinating chickens against Salmonella Enteritidis (SE) using a vaccine candidate strain (JOL919), constructed by deleting the lon and cpxR genes from a wild-type SE using an allelic exchange method. In present study day old chickens were inoculated with 1×10(7)cfu (colony forming unit) of JOL919 per os. We measured cell-mediated immunity, protective efficacy and extent of apoptosis induction in splenocytes. Seven days post-immunization, the number of CD3+CD4+ and CD3+ CD8+ T cells was significantly higher in the immunized group compared to the control group, indicating a significant augmentation of systemic immune response. The internal organs of chickens immunized with JOL919 had a significantly lower challenge-strain recovery, indicating effective protection and clearance of the challenge strain. Post-challenge, the number of apoptotic cells in the immunized group was significantly lower than in the control group. Additionally, AV/PI (Annexin V/propidium iodide) staining was performed to differentiate between apoptotic cells and necrotic cells, which corroborated TUNEL-assay (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling) results. The proportions of AV+/PI- and AV+/PI+ cells, which represent the proportions of early apoptotic and late apoptotic/early necrotic cells present, respectively, were significantly lower in the immunized group. Our findings suggest that the apoptotic splenocytes in immunized chickens significantly decreased in number, which occurred concomitantly with a significant rise in systemic immune response and bacterial clearance. This suggests that inhibition of apoptosis may be a marker of protection efficacy in immunized chickens.

Reduction of Salmonella Enteritidis in the spleens of hens by bacterins that vary in fimbrial protein SefD

The objective of this research was to determine whether variation in the presence of fimbrial protein SefD would impact efficacy of bacterins as measured by recovery of Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) from the spleens of hens. Two bacterins were prepared that varied in SefD content. Also, two adjuvants were tested, namely, water-in-oil and aluminum hydroxide gel (alum). Control groups for both adjuvant preparations included infected nonvaccinated hens and uninfected nonvaccinated hens. At 21 days postinfection, Salmonella Enteritidis was recovered from 69.7%, 53.1%, and 86.0% from the spleens of all hens vaccinated with bacterins lacking SefD, bacterins that included SefD, and infected nonvaccinated control hens, respectively. No Salmonella was recovered from uninfected nonvaccinates. Results from individual trials showed that both bacterins reduced positive spleens, but that the one with SefD was more efficacious. Alum adjuvant had fewer side effects on hens and egg production as compared to water-in-oil. However, adjuvant did not change the relative recovery of Salmonella Enteritidis from spleens. These results suggest that SefD is a promising target antigen for improving the efficacy of immunotherapy in hens, and is intended to reduce Salmonella Enteritidis in the food supply.

Comparative evaluation of Salmonella Enteritidis ghost vaccines with a commercial vaccine for protection against internal egg contamination with Salmonella

The study was conducted for the comparative evaluation of the vaccine potential of Salmonella Enteritidis (S. Enteritidis, SE) ghost, SE ghost carrying Escherichia coli heat labile enterotoxin B subunit (LTB) protein, and a commercial vaccine. Group A chickens were used as a non-vaccinated control, group B chickens were immunized with the ghost carrying LTB protein, group C chickens were immunized with the ghost and, group D chickens were immunized with a commercial vaccine. Group D chickens showed the swelling at the injection site, while no adverse reactions were observed at injection sites of the group B and C chickens. Chickens from the immunized groups B, C, and D demonstrated significant increases in plasma IgG, intestinal secretory IgA levels, and antigen-specific lymphocyte proliferative responses. After challenge with a virulent SE strain via intravenous route, groups B, C, and D showed significantly higher egg production and lower internal egg contamination and lower recovery of the challenge strain from internal organs compared to non-immunized-challenged control group A. In conclusion, these data indicate that immunization of chickens with the ghost and ghost carrying LTB is safe, without causing any adverse reaction, and is effective as the commercial vaccine in terms of reduction in internal egg contamination and internal organ colonization of Salmonella.

An immunogenic Salmonella ghost confers protection against internal organ colonization and egg contamination

The tightly regulated expression of the PhiX174 lysis gene E from a multi-copy plasmid led to the stable production of an Salmonella Enteritidis bacterial ghost. The present study was conducted to evaluate induction of the humoral and cell-mediated immune responses induced after single or double intramuscular immunization with the S. Enteritidis ghost and to assess its protective effect on colonization of the intestinal tract, visceral and reproductive organs, internal egg contamination, and egg production of laying chickens. A total of 60 chickens were equally divided into three groups (n=20); group A (non-immunized control), group B (immunized at 8 and 16 weeks of age) and group C (immunized at 16th week of age). Chickens from both immunized groups B and C demonstrated significant increases in plasma IgG, intestinal secretory IgA levels, and antigen-specific lymphocyte proliferative responses. The population of CD3+CD4+ positive T cells in the immunized chickens was also significantly increased after immunization and virulent challenge. In addition, the immunized groups B and C showed significantly higher egg production and a lower percentage of S. Enteritidis contaminated eggs after challenge compared to those of group A. A comparison of challenge strain isolation from the immunized-challenged and non-immunized-challenged layer hens showed that the double immunization group induced excellent protection against intestinal, liver, splenic, and ovarian Salmonella colonization; however, the single immunized chickens showed lower counts only in the splenic and ovarian organs. Overall, the data give compelling evidence that vaccination with the S. Enteritidis ghost induced robust protective immunity against experimental avian salmonellosis and may contribute to the reduce incidence of egg contamination.

Salmonella enterica serovar enteritidis ghosts carrying the Escherichia coli heat-labile enterotoxin B subunit are capable of inducing enhanced protective immune responses

The Escherichia coli heat-labile enterotoxin B subunit (LTB) is a potent vaccine adjuvant. Salmonella enterica serovar Enteritidis ghosts carrying LTB (S. Enteritidis-LTB ghosts) were genetically constructed using a novel plasmid, pJHL187-LTB, designed for the coexpression of the LTB and E lysis proteins. S. Enteritidis-LTB ghosts were characterized using scanning electron microscopy to visualize their transmembrane tunnel structures. The expression of LTB in S. Enteritidis-LTB ghost preparations was confirmed by immunoblot and enzyme-linked immunosorbent assays. The parenteral adjuvant activity of LTB was demonstrated by immunizing chickens with either S. Enteritidis-LTB ghosts or S. Enteritidis ghosts. Chickens were intramuscularly primed at 5 weeks of age and subsequently boosted at 8 weeks of age. In total, 60 chickens were equally divided into three groups (n = 20 for each): group A, nonvaccinated control; group B, immunized with S. Enteritidis-LTB ghosts; and group C, immunized with S. Enteritidis ghosts. Compared with the nonimmunized chickens (group A), the immunized chickens (groups B and C) exhibited increased titers of plasma IgG and intestinal secretory IgA antibodies. The CD3(+) CD4(+) subpopulation of T cells was also significantly increased in both immunized groups. Among the immunized chickens, those in group B exhibited significantly increased titers of specific plasma IgG and intestinal secretory IgA (sIgA) antibodies compared with those in group C, indicating the immunomodulatory effects of the LTB adjuvant. Furthermore, both immunized groups exhibited decreased bacterial loads in their feces and internal organs. These results indicate that parenteral immunization with S. Enteritidis-LTB ghosts can stimulate superior induction of systemic and mucosal immune responses compared to immunization with S. Enteritidis ghosts alone, thus conferring efficient protection against salmonellosis.

Construction of a recombinant-attenuated Salmonella Enteritidis strain secreting Escherichia coli heat-labile enterotoxin B subunit protein and its immunogenicity and protection efficacy against salmonellosis in chickens

A live attenuated Salmonella Enteritidis (SE) strain secreting Escherichia coli heat-labile enterotoxin B subunit (LTB) protein was constructed as a new vaccine candidate. The comparative effect of this vaccine candidate was evaluated with a previously reported SE vaccine, JOL919. An asd+, p15A ori plasmid containing eltB-encoding LTB was introduced into a ΔlonΔcpxRΔasd SE strain, and designated as JOL1364. In a single immunization experiment, group A chickens were orally inoculated with phosphate-buffered saline as a control, group B chickens were orally immunized with JOL919, and group C chickens were orally immunized with JOL1364. The immunized groups B and C showed significantly higher systemic, mucosal and cellular immune responses as compared to those of the control group. In addition, the immunized group C showed significantly higher mucosal and cellular immune responses as compared to those of the immunized group B at the 1st week post-immunization. In the examination of protection efficacy, the immunized groups B and C showed lower gross lesion scores in the liver and spleen, and lower bacterial counts of SE challenge strain in the liver, spleen, and caeca as compared to those of the control group. The number of SE-positive birds was significantly lower in the immunized group C as compared to that of the control group at the 14th day post-challenge. In addition, the number of birds carrying the challenge strain in the caeca was significantly lower in the immunized group C than those in the immunized group B and control group at the 7th and 14th day post-challenge. These results indicate that immunization with the JOL1364 vaccine candidate can induce higher mucosal and cellular immune responses than those of the JOL919 for efficient protection against salmonellosis.

Development of a biosafety enhanced and immunogenic Salmonella enteritidis ghost using an antibiotic resistance gene free plasmid carrying a bacteriophage lysis system

In the development of genetically inactivated bacterial vaccines, plasmid retention often requires the antibiotic resistance gene markers, the presence of which can cause the potential biosafety hazards such as the horizontal spread of resistance genes. The new lysis plasmid was constructed by utilizing the approach of balanced-lethal systems based on auxotrophic gene Aspartate semialdehyde dehydrogenase (asd). The PhiX174 lysis gene E and λPR37-cI857 temperature-sensitive regulatory system was cloned in the asd gene positive plasmid and this novel approach allowed the production of antibiotic resistance marker free Salmonella Enteritidis (S. Enteritidis) ghost. The immunogenic potential of the biosafety enhanced antibiotic resistance gene free S. Enteritidis ghost was evaluated in chickens by employing the prime-boost vaccination strategy using a combination of oral and intramuscular routes. A total of 75 two-week-old chickens were equally divided into five groups: group A (non-immunized control), group B (intramuscularly primed and boosted), group C (primed intramuscularly and boosted orally), group D (primed and boosted orally), and group E (primed orally and boosted intramuscularly). Chickens from all immunized groups demonstrated significant increases in plasma IgG, intestinal secretory IgA levels, and antigen-specific lymphocyte proliferative response. After a virulent S. Enteritidis challenge, all immunized groups showed fewer gross lesions and decreased bacterial recovery from organs in comparison with the non-immunized control group. Among the immunized chickens, groups B and D chickens showed optimized protection, indicating that the prime-booster immunization with the ghost via intramuscular or oral route is efficient. Taken together, our results demonstrate that an antibiotic resistance gene free lysis plasmid was successfully constructed and utilized for production of safety enhanced S. Enteritidis ghost, which can be used as a safe and effective vaccine against virulent S. Enteritidis infections.

Vaccination of chickens with SPI1-lon and SPI1-lon-fliC mutant of Salmonella enterica Serovar Enteritidis

The prevalence of Salmonella enterica serovar Enteritidis is gradually decreasing in poultry flocks in the EU, which may result in the demand for a vaccine that allows for the differentiation of vaccinated flocks from those infected by wild-type S. Enteritidis. In this study, we therefore constructed a (Salmonella Pathogenicity Island 1) SPI1-lon mutant with or without fliC encoding for S. Enteritidis flagellin. The combination of SPI1-lon mutations resulted in attenuated but immunogenic mutant suitable for oral vaccination of poultry. In addition, the vaccination of chickens with the SPI1-lon-fliC mutant enabled the serological differentiation of vaccinated and infected chickens. The absence of fliC therefore did not affect the immunogenicity of the vaccine strain and allowed for serological differentiation of the vaccinated chickens. The SPI1-lon-fliC mutant is therefore a suitable marker vaccine strain for oral vaccination of poultry.

Oral immunization with an attenuated Salmonella Gallinarum mutant as a fowl typhoid vaccine with a live adjuvant strain secreting the B subunit of Escherichia coli heat-labile enterotoxin

BACKGROUND

The Salmonella Gallinarum (SG) lon/cpxR deletion mutant JOL916 was developed as a live vaccine candidate for fowl typhoid (FT), and a SG mutant secreting an Escherichia coli heat-labile enterotoxin B subunit (LTB), designated JOL1229, was recently constructed as an adjuvant strain for oral vaccination against FT. In this study, we evaluated the immunogenicity and protective properties of the SG mutant JOL916 and the LTB adjuvant strain JOL1229 in order to establish a prime and boost immunization strategy for each strain. In addition, we compared the increase in body weight, the immunogenicity, the egg production rates, and the bacteriological egg contamination of these strains with those of SG 9R, a widely used commercial vaccine.

RESULTS

Plasma IgG, intestinal secretory IgA (sIgA), and cell-mediated responses were significantly induced after a boost inoculation with a mixture of JOL916 and JOL1229, and significant reductions in the mortality of chickens challenged with a wild-type SG strain were observed in the immunized groups. There were no significant differences in increases in body weight, cell-mediated immune responses, or systemic IgG responses between our vaccine mixture and the SG 9R vaccine groups. However, there was a significant elevation in intestinal sIgA in chickens immunized with our mixture at 3 weeks post-prime-immunization and at 3 weeks post-boost-immunization, while sIgA levels in SG 9R-immunized chickens were not significantly elevated compared to the control. In addition, the SG strain was not detected in the eggs of chickens immunized with our mixture.

CONCLUSION

Our results suggest that immunization with the LTB-adjuvant strain JOL1229 can significantly increase the immune response, and provide efficient protection against FT with no side effects on body weight, egg production, or egg contamination.

Immunological changes at point-of-lay increase susceptibility to Salmonella enterica Serovar enteritidis infection in vaccinated chickens

Chicken eggs are the main source of human Salmonella enterica serovar Enteritidis infection. S. Enteritidis infects the oviduct and ovary of the chicken leading to infection of developing eggs. Therefore, control in poultry production is a major public health priority. Vaccination of hens has proved successful in control strategies in United Kingdom leading to a 70% drop in human cases since introduced. However, as hens reach sexual maturity they become immunosuppressed and it has been postulated this leads to increased susceptibility to Salmonella infection. In this study we define the changes to the systemic and reproductive tract-associated immune system of hens throughout sexual development by flow cytometry and histology and determine changes in susceptibility to experimental S. Enteritidis challenge in naive and vaccinated hens. Changes to both systemic and local immune systems occur in chickens at sexual development around 140 days of age. The population of several leukocyte classes drop, with the greatest fall in CD4+ lymphocyte numbers. Within the developing reproductive tract there an organised structure of lymphocytic aggregates with γδ-T lymphocytes associated with the mucosa. At point-of-lay, this organised structure disappears and only scattered lymphocytes remain. Protection against Salmonella challenge is significantly reduced in vaccinated birds at point-of-lay, coinciding with the drop in CD4+ lymphocytes. Susceptibility to reproductive tract infection by Salmonella increased in vaccinated and naïve animals at 140 and 148 days of age. We hypothesise that the drop in γδ-T lymphocytes in the tract leads to decreased innate protection of the mucosa to infection. These findings indicate that systemic and local changes to the immune system increase the susceptibility of hens to S. Enteritidis infection. The loss of protective immunity in vaccinated birds demonstrates that Salmonella control should not rely on vaccination alone, but as part of an integrated control strategy including biosecurity and improved animal welfare.

A review of vaccine development and research for industry animals in Korea

Vaccination has proven to be the most cost-effective strategy for controlling a wide variety of infectious diseases in humans and animals. For the last decade, veterinary vaccines have been substantially developed and demonstrated their effectiveness against many diseases. Nevertheless, new vaccines are greatly demanded to effectively control newly- and re-emerging pathogens in livestock. However, development of veterinary vaccines is a challenging task, in part, due to a variety of pathogens, hosts, and the uniqueness of host-susceptibility to each pathogen. Therefore, novel concepts of vaccines should be explored to overcome the limitation of conventional vaccines. There have been greatly advanced in the completion of genomic sequencing of pathogens, the application of comparative genomic and transcriptome analysis. This would facilitate to open opportunities up to investigate a new generation of vaccines; recombinant subunit vaccine, virus-like particle, DNA vaccine, and vector-vehicle vaccine. Currently, such types of vaccines are being actively explored against various livestock diseases, affording numerous advantages over conventional vaccines, including ease of production, immunogenicity, safety, and multivalency in a single shot. In this articles, the authors present the current status of the development of veterinary vaccines at large as well as research activities conducted in Korea.

Characterization of a novel inactivated Salmonella enterica serovar Enteritidis vaccine candidate generated using a modified cI857/λ PR/gene E expression system

A new strategy to develop an effective vaccine is essential to control food-borne Salmonella enterica serovar Enteritidis infections. Bacterial ghosts (BGs), which are nonliving, Gram-negative bacterial cell envelopes, are generated by expulsion of the cytoplasmic contents from bacterial cells through controlled expression using the modified cI857/λ P(R)/gene E expression system. In the present study, the pJHL99 lysis plasmid carrying the mutated lambda pR37-cI857 repressor and PhiX174 lysis gene E was constructed and transformed in S. Enteritidis to produce a BG. Temperature induction of the lysis gene cassette at 42°C revealed quantitative killing of S. Enteritidis. The S. Enteritidis ghost was characterized using scanning and transmission electron microscopy to visualize the transmembrane tunnel structure and loss of cytoplasmic materials, respectively. The efficacy of the BG as a vaccine candidate was evaluated in a chicken model using 60 10-day-old chickens, which were divided into four groups (n = 15), A, B, C, and D. Group A was designated as the nonimmunized control group, whereas the birds in groups B, C, and D were immunized via the intramuscular, subcutaneous, and oral routes, respectively. The chickens from all immunized groups showed significant increases in plasma IgG and intestinal secretory IgA levels. The lymphocyte proliferation response and CD3(+) CD4(+) and CD3(+) CD8(+) T cell subpopulations were also significantly increased in all immunized groups. The data indicate that both humoral and cell-mediated immune responses are robustly stimulated. Based on an examination of the protection efficacy measured by observations of gross lesions in the organs and bacterial recovery, the candidate vaccine can provide efficient protection against virulent challenge.