Efficacy for a New Live AttenuatedSalmonellaEnteritidis Vaccine Candidate to Reduce Internal Egg Contamination

Safety of the Salmonella enterica serotype Dublin strain Sdu189-derived live attenuated vaccine—A pilot study

Salmonella enterica serovar Dublin (S. Dublin) is an important zoonotic pathogen with high invasiveness. In the prevention and control of the Salmonella epidemic, the live attenuated vaccine plays a very important role. To prevent and control the epidemic of S. Dublin in cattle farms, the development of more effective vaccines is necessary. In this study, we constructed two gene deletion mutants, Sdu189ΔspiC and Sdu189ΔspiCΔaroA, with the parental strain S. Dublin Sdu189. The immunogenicity and protective efficacy were evaluated in the mice model. First, both mutant strains were much less virulent than the parental strain, as determined by the 50% lethal dose (LD₅₀) for specific pathogen-free (SPF) 6-week-old female BALB/c mice. Second, the specific IgG antibody level and the expression level of cytokine TNF-α, IFN-γ, IL-4, and IL-18 were increased significantly in the vaccinated mice compared to the control group. In addition, the deletion strains were cleared rapidly from organs of immunized mice within 14 d after immunization, while the parental strain could still be detected in the spleen and liver after 21 d of infection. Compared with the parental strain infected group, no obvious lesions were detected in the liver, spleen, and cecum of the deletion strain vaccinated groups of mice. Immunization with Sdu189ΔspiC and Sdu189ΔspiCΔaroA both provided 100% protection against subsequent challenges with the wild-type Sdu189 strain. These results demonstrated that these two deletion strains showed the potential as live attenuated vaccines against S. Dublin infection. The present study established a foundation for screening a suitable live attenuated Salmonella vaccine.

Evaluation of Immune Responses and Protective Efficacy of a Novel Live Attenuated Salmonella Enteritidis Vaccine Candidate in Chickens

An ideal vaccine for controlling Salmonella infection in chicken flocks should be safe, inducing both humoral and cellular immunity. Live attenuated vaccines against Salmonella Enteritidis (S. Enteritidis) have been used as a potential control method of Salmonella infection in the poultry industry. However, live attenuated vaccines can persistently infect poultry for long periods and can become virulent revertant strains. In this study, we assessed the immune responses and protective efficacy of a temperature-sensitive attenuated S. Enteritidis mutant as a potential vaccine candidate. In addition, we evaluated the combined vaccine administration methods to maximize both humoral and cellular immune responses in chickens induced by the vaccine candidate. Immune responses and protective efficacy were compared between the Oral/IM group, vaccinated using one oral dose at four weeks old and a booster intramuscular dose at seven weeks old, and the IM/Oral group, vaccinated using one intramuscular dose at four weeks old and a booster oral dose at seven weeks old. The Oral/IM group showed stronger immune responses than those of the IM/Oral group. Spleens from the Oral/IM group showed a promising tendency of reduction of challenged Salmonella compared with those of other groups. Overall, the results indicated that the S. Enteritidis mutant strain is a promising live attenuated vaccine candidate with good efficacy.

Mucosal Vaccine Development for Veterinary and Aquatic Diseases

Because most pathogens and food antigens enter the host via the mucosal surfaces, effective mucosal immunity is critical for maintaining homeostasis through immune regulation, tolerance, and induction of effective immune responses when needed. Thus the mucosa-associated lymphoid tissues represent an important target for vaccination. Indeed, more than 20 years of research have clearly demonstrated the benefits of mucosal vaccination versus systemic vaccination. Such benefits include local induction of secretory immunoglobulin A (SIgA) as well as activation and maturation of mucosal dendritic cells, homing of effector cells to the mucosal surfaces, expression of specific host defense peptides, and other innate effector molecules. In addition, mucosal vaccination offers the opportunity to induce colostral and lactogenic immunity during pregnancy and the possibility of avoiding neutralization of early life vaccines by maternal antibodies, both of which are critical for protecting the most susceptible from infectious diseases. Moreover, mucosal administration offers the advantage of inducing both effective systemic immunity and mucosal immunity, enhancing vaccine efficacy and providing improved protection. A number of animal vaccines are already administered via the mucosal surfaces, with many more to come over the next few years. It is gratifying to see that veterinary vaccine development has yet again taken a leadership role in exploring innovative approaches and technologies to mucosal vaccination. For the veterinary field, considerations for mucosal vaccine development and use necessarily include costs (often pennies per dose), mass delivery that preferably avoids animal restraint, and economic and trade considerations. In this chapter, we provide an overview of some of the existing vaccine technologies and discuss their advantages and disadvantages.

Immunogenic potential and protective efficacy of a sptP deletion mutant of Salmonella Enteritidis as a live vaccine for chickens against a lethal challenge

Salmonella Enteritidis (SE) is a highly adapted pathogen causing severe economic losses in the poultry industry worldwide. Chickens infected by SE are a major source of human food poisoning. Vaccination is an effective approach to control SE infections. This study evaluated the immunogenicity and protective efficacy of a SE sptP deletion mutant (C50336ΔsptP) as a live attenuated vaccine (LAV) candidate in chickens. 14 day-old specific pathogen-free (SPF) chickens were intramuscularly immunized with various doses of C50336ΔsptP. Several groups of chickens were challenged with the virulent wild-type SE strain Z-11 via the same route at 14 days post vaccination. Compared to the control group, the groups vaccinated with 1 × 10⁶, 1 × 10⁷ and 1 × 10⁸ colony-forming units (CFU) of C50336ΔsptP exhibited no clinical symptoms after immunization. Only slight pathological changes occurred in the organs of the 1 × 10⁹ CFU vaccinated group. C50336ΔsptP bacteria were cleared from the organs of immunized chickens within 14 days after vaccination. Lymphocyte proliferation and serum cytokine analyses indicated that significant cellular immune responses were induced after the vaccination of C50336ΔsptP. Compared to the control group, specific IgG antibody levels increased significantly in vaccinated chickens, and the levels increased markedly after the challenge. The 1 × 10⁷, 1 × 10⁸, and 1 × 10⁹ CFU vaccinated chickens groups showed no clinical symptoms or pathological changes, and no death after the lethal challenge. Whereas severe clinical signs of disease and pathological changes were observed in the control group chickens after the challenge. These results suggest that a single dose of C50336ΔsptP could be an effective LAV candidate to against SE infection in chickens.

Response to a Salmonella Enteritidis challenge in old laying hens with different vaccination histories

Extending the laying period of laying hens is beneficial for economic and sustainability purposes. Because vaccines were designed with a shorter laying period envisaged, it is unclear whether current Salmonella vaccines can provide sufficient levels of protection against infection at an older age. The purpose of this experiment was to determine the efficacy of early rearing vaccination schemes against Salmonella challenge late in the laying period. There were four treatment groups: birds that had not been vaccinated (Group 1), birds vaccinated with live Salmonella Enteritidis (SE) (Group 2), with live and inactivated SE (Group 3), or with live SE and live Salmonella Typhimurium (Group 4). At the end of the laying period, the birds were transported from the laying farm to the research facility where they were orally challenged with 2.06 × 109 colony-forming units SE at around 82 wk of age. Hens were euthanized and bacteriology was performed on cecum, liver, spleen, and follicular fluid samples to determine SE colonization 7 and 14 d after challenge. Clinical and bacteriological findings of hens vaccinated with different vaccination schemes and the non-vaccinated control group were compared. No significant differences in SE colonization were found for vaccinated groups compared to the non-vaccinated control group. This may be a result of waning immunity due to the long time between vaccination and challenge. Also, as vaccination took place in the rearing period in the field, initial levels of immunity may not have been optimal due to shortcomings in the vaccination technique. Furthermore, the results of this study may have been affected by differences in age, breed, and origin between the groups. Therefore, controlled studies from early age onwards are necessary for more accurate comparisons between vaccines.

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.

Epidemic characterization and molecular genotyping of Shigella flexneri isolated from calves with diarrhea in Northwest China

BACKGROUND

The widespread presence of antibiotics resistance genes in pathogenic bacteria can cause enormous problems. Food animals are one of the main reservoirs of intestinal pathogens that pose a potential risk to human. Analyzing the epidemiological characteristics and resistance patterns of Shigella flexneri in calves is necessary for animal and human health.

METHODS AND RESULTS

A total of 54 Shigella flexneri isolates, including six serotypes (1a, 2a, 2b, 4a, 6 and Xv), were collected from 837 fecal samples obtained from 2014 to 2016. We performed pulsed-field gel electrophoresis (PFGE) and applied the restriction enzyme NotI to analyze the genetic relatedness among the 54 isolates and to categorize them into 31 reproducible and unique PFGE patterns. According to the results of antimicrobial susceptibility tests, all 26 Shigella flexneri 2a serotypes were resistant to cephalosporin and/or fluoroquinolones. The genes bla_TEM-1 , bla_OXA-1 , and bla_CTX-M-14 were detected in 19 cephalosporin-resistant S. flexneri 2a isolates. Among 14 fluoroquinolone-resistant isolates, the aac(6')-Ib-cr gene was largely present in each strain, followed by qnrS (5). Only one ciprofloxacin-resistant isolate harbored the qepA gene. Sequencing the quinolone resistance determining regions (QRDRs) of the fluoroquinolone-resistant isolates revealed two point mutations in gyrA (S83 L, D87N/Y) and a single point mutation in parC (S80I). Interestingly, two gyrA (D87N/Y) strains were resistant to ciprofloxacin.

CONCLUSIONS

The current study enhances our knowledge of Shigella in cattle, although continual surveillance is necessary for the control of shigellosis. The high level of cephalosporin and/or fluoroquinolone resistance in Shigella warns us of a potential risk to human and animal health.

16S ribosomal RNA sequencing and molecular serotyping of Avibacterium paragallinarum isolated from Indian field conditions

AIM

This study was aimed at identifying Indian field isolates of Avibacterium paragallinarum on both molecular as well as serological levels that cause infectious coryza in chickens.

MATERIALS AND METHODS

Species-specific polymerase chain reaction (HPG-2 PCR), and 16S ribosomal RNA (rRNA) sequencing were employed for molecular identification. Whereas, multiplex PCR technique was used for serological identification of Indian field isolates of A. paragallinarum.

RESULTS

All three field isolates were identified as A. paragallinarum using HPG-2 PCR. The species-specific PCR results were validated using 16S rRNA sequencing. The partial 16S rRNA sequences obtained from all three isolates showed 96-99% homology with the NCBI database reference strains of A. paragallinarum. The aligned partial sequences of 16S rRNA were submitted to GenBank, and accession numbers were obtained. Multiplex PCR-based molecular serotyping showed that there are three serotypes of field isolates of A. paragallinarum, namely, strain IND101 is serovar A, strain IND102 is serovar B, and strain IND103 is serovar C.

CONCLUSION

HPG-2 PCR, 16S rRNA sequencing, and multiplex PCR are proved to be more accurate, sensitive, and reliable diagnostic tools for molecular and serological identification of A. paragallinarum field isolates. These diagnostic methods can substitute conventional cultural characterization and would be much valuable to formulate quick and correct prevention and control measures against this detrimental poultry pathogen.

Vaccination against Salmonella Infection: the Mucosal Way

Salmonella enterica subspecies enterica includes several serovars infecting both humans and other animals and leading to typhoid fever or gastroenteritis. The high prevalence of associated morbidity and mortality, together with an increased emergence of multidrug-resistant strains, is a current global health issue that has prompted the development of vaccination strategies that confer protection against most serovars. Currently available systemic vaccine approaches have major limitations, including a reduced effectiveness in young children and a lack of cross-protection among different strains. Having studied host-pathogen interactions, microbiologists and immunologists argue in favor of topical gastrointestinal administration for improvement in vaccine efficacy. Here, recent advances in this field are summarized, including mechanisms of bacterial uptake at the intestinal epithelium, the assessment of protective host immunity, and improved animal models that closely mimic infection in humans. The pros and cons of existing vaccines are presented, along with recent progress made with novel formulations. Finally, new candidate antigens and their relevance in the refined design of anti-Salmonella vaccines are discussed, along with antigen vectorization strategies such as nanoparticles or secretory immunoglobulins, with a focus on potentiating mucosal vaccine efficacy.