Safety, Protective Immunity, and DIVA Capability of a Rough Mutant Salmonella Pullorum Vaccine Candidate in Broilers

Lipopolysaccharide structural modification in Salmonella Gallinarum targeting lipid a deacylation and O-antigen reduces virulence and endotoxicity with competitive protection against a wild-type challenge in chickens

Fowl typhoid (FT), caused by Salmonella Gallinarum (SG), inflicts a significant economic burden on the poultry industry. Our study focused on a non-reversible gene deletion to develop a safe and effective SG vaccine strain through lipopolysaccharide (LPS) structural modification. The virulence-attenuated SG JOL914 strain, generated by deleting the global regulator lon gene, was engineered by in-frame deletions targeting the LPS structure. Interruption on LPS deacylation was introduced by pagL deletion, JOL2997, to mitigate endotoxicity induced by the live vaccine. The O-antigen was truncated by rfaL deletion, JOL3004, to compromise virulence and facilitate Differentiating Infected from Vaccinated Animals (DIVA). Both genes were depleted in JOL3016 (ΔlonΔpagLΔrfaL) for their compounding effects. Subcutaneous administration of the engineered strains in chickens showed reduced endotoxicity, particularly demonstrated by JOL3016 with 2.55-fold and 3.79-fold reductions in TNF-α and IL-1β, respectively. Furthermore, discernible effects on body weight gain and the absence of pathological signs demonstrated the safety profiles of the inoculated strains. Administration of mutant strains substantially increased antigen-specific IgY, sIgA, CD4+, and CD8+ T cells, supporting immune response elicitation. The absence of antibodies against O-antigen in birds immunized with JOL3004 and JOL3016 demonstrated their DIVA capability. The result was corroborated by improved protection with a rational body weight gain and minimal tissue distortion following an SG WT challenge. JOL2997-immunized birds showed promising survival, and negligible invasion of the challenge strain in vital organs, highlighting its protective efficacy. This study underscores the potential of bioengineered vaccine strains to improve poultry health and productivity, reinforcing the necessity for ongoing vaccine development research.

Deletion of pagL and arnT genes involved in LPS structure and charge modulation in the Salmonella genome confer reduced endotoxicity and retained efficient protection against wild-type Salmonella Gallinarum challenge in chicken

Fowl typhoid (FT) poses a significant threat to the poultry industry and can cause substantial economic losses, especially in developing regions. Caused by Salmonella Gallinarum (SG), vaccination can prevent FT. However, existing vaccines, like the SG9R strain, have limitations, including residual virulence and potential reversion of pathogenicity. This study aims to develop safer and more effective SG vaccine strains through targeted genetic modifications, focusing on genes involved in lipopolysaccharide (LPS) biosynthesis and modification. We evaluated two novel mutant SG strains, JOL3015 and JOL3016, carrying in-frame deletions in ΔlonΔrfaLΔarnT and ΔlonΔrfaLΔpagL, respectively. Intramuscular immunisation of 4-week-old young birds with JOL3015 and JOL3016 strains showed minimal impact on their growth. However, the immunisation significantly increased antigen-specific IgY, sIgA secretion, and CD4+ and CD8+ T-cell responses while inducing lower pro-inflammatory cytokine levels than SG9R. Histopathological evaluations revealed substantial protection in the immunised birds, with minimal tissue damage and inflammatory responses, thus reducing the in vivo bacterial burden. Furthermore, none of the immunised birds died. This outcome highlights the significant safety and protection the selected genetic modifications conferred. Our results indicate that JOL3016 provided comparable protective outcomes on par with SG9R, yet with significantly lower endotoxicity responses during the lethal challenge with SG WT JOL422. The novel detoxified SG strains, particularly JOL3016, offer a promising alternative to existing vaccines for FT. They provide effective protection with minimal impact on poultry growth, thereby minimising the risks associated with reversion and endotoxicity. The study highlights the potential of genetically engineered vaccine strains in improving poultry health and productivity, emphasising the importance of continued research.

Progress in the application of Salmonella vaccines in poultry: A mini review

Salmonella is a critical group of zoonotic pathogens that are widely spread in poultry, causing avian salmonellosis. This disease usually leads to significant reductions in poultry performance, including reduced egg production in laying hens, decreased hatchability in chicks, and retarded growth in broilers. As a result, worldwide poultry industry suffers serious economic losses. Vaccination serves as an essential strategy for preventing Salmonella infection in poultry, effectively reducing susceptibility and alleviating disease symptoms, while also minimizing fecal shedding and environmental contamination. This subsequently diminishes public health risks. Various Salmonella vaccines can induce humoral and cellular immune responses to different extents. Therefore, a thorough understanding of the immune defense mechanisms, especially adaptive immune responses in poultry infected with Salmonella, is crucial for the development of Salmonella vaccines. This review summarizes the progress in the application of Salmonella vaccines in poultry, including adaptive immune responses induced by Salmonella and vaccines targeting the predominant circulating serotypes in poultry. It also provides an insight into the future of poultry-origin Salmonella vaccines.

Efficient screening of adsorbed receptors for Salmonella phage LP31 and identification of receptor-binding protein

The adsorption process is the first step in the lifecycle of phages and plays a decisive role in the entire infection process. Identifying the adsorption mechanism of phages not only makes phage therapy more precise and efficient but also enables the exploration of other potential applications and modifications of phages. Phage LP31 can lyse multiple Salmonella serotypes, efficiently clearing biofilms formed by Salmonella enterica serovar Enteritidis (S. Enteritidis) and significantly reducing the concentration of S. Enteritidis in chicken feces. Therefore, LP31 has great potential for many practical applications. In this study, we established an efficient screening method for phage infection-related genes and identified a total of 10 genes related to the adsorption process of phage LP31. After the construction of strain C50041ΔrfaL 58-358, it was found that the knockout strain had a rough phenotype as an O-antigen-deficient strain. Adsorption rate and transmission electron microscopy experiments showed that the receptor for phage LP31 was the O9 antigen of S. Enteritidis. Homology comparison and adsorption experiments confirmed that the tail fiber protein Lp35 of phage LP31 participated in the adsorption process as a receptor-binding protein. IMPORTANCE A full understanding of the interaction between phages and their receptors can help with the development of phage-related products. Phages like LP31 with the tail fiber protein Lp35, or a closely related protein, have been reported to effectively recognize and infect multiple Salmonella serotypes. However, the role of these proteins in phage infection has not been previously described. In this study, we established an efficient screening method to detect phage adsorption to host receptors. We found that phage LP31 can utilize its tail fiber protein Lp35 to adsorb to the O9 antigen of S. Enteritidis, initiating the infection process. This study provides a great model system for further studies of how a phage-encoded receptor-binding protein (RBP) interacts with its host's RBP binding target, and this new model offers opportunities for further theoretical and experimental studies to understand the infection mechanism of phages.

JMM Profile: Salmonella enterica serovar Gallinarum, biovars Pullorum and Gallinarum

Salmonella serovar Gallinarum has two distinct biovars, Pullorum and Gallinarum. They are host-adapted avian pathogens that infect a number of wild and domesticated species but they pose a particular threat to farmed and backyard chickens and turkeys. Both biovars cause invasive and septicaemic disease, often resulting in high mortality. Pullorum is transmitted in eggs and typically affects birds soon after hatch. Gallinarum may cause disease in any age of bird, which often progresses through mature flocks. The establishment of clean breeding stock has resulted in freedom from the pathogens in many countries although even in these territories sporadic incursions still occur.

Contribution of GalU to biofilm formation, motility, antibiotic and serum resistance, and pathogenicity of Salmonella Typhimurium

Introduction

Salmonella Typhimurium is the leading cause of foodborne illnesses in China, resulting in major epidemics and economic losses in recent years. Uridine diphosphate-glucose pyrophosphorylase galU plays an important role in thebiosynthesis of the bacterial envelope. Herein, we evaluated the role of galU in S. Typhimurium infection in chicken.

Methods

A galU gene mutant was successfully constructed by red homologous recombination technology, and biological characteristics were studied.

Results

The galU mutant strain had a rough phenotype;was defective in biofilm formation, autoagglutination, and motility; exhibited greater sensitivity to most antibiotics, serum, and egg albumen; and had lowercapacity for adhesion to chicken embryo fibroblasts cell line (DF-1). The galU mutant showed dramatically attenuated pathogenicity in chicken embryos (100,000-fold), BALB/c mice (420-fold), and chicks (100-fold).

Discussion

The results imply that galU is an important virulence factor in the pathogenicity of S. Typhimurium, and it may serve a target for the development of veterinary drugs, providing a theoretical basis for the prevention and control of S. Typhimurium.

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.

Assessing an O-antigen deficient, live attenuated Salmonella Gallinarium strain that is DIVA compatible, environmentally safe, and protects chickens against fowl typhoid

The objective of the present study was to create a highly attenuated, safe Salmonella Gallinarium (SG) vaccine strain for chicken vaccination against fowl typhoid (FT) diseases. The SG vaccine strain (SGVS) consists of three virulence-related gene deletions, namely, lon, cpxR, and rfaL. The parent strain (SGPS) with Δlon ΔcpxR genotype was utilized as the host strain for in-frame rfaL gene deletion by lambda red recombination. The SGVS was highly attenuated with improved environmental safety by zero fecal contamination beyond seven days for both oral and intramuscular immunization routes. Upon inoculation into 1-month-old young chicken, no vaccine-induced adverse behaviors were observed and did not cause a chronic state of infection as the SG wild-type strain did. Immunization of chicken elicited both humoral and cell-mediated immune responses demarcated by, IgY antibody assessment, T-cell responses in peripheral blood mononuclear cells, and the induction of immunomodulatory cytokines, IFN-γ, IL-2, IL-12, and IL-4 to resemble both Th1 and Th2 type of immune responses. The immunological assessment revealed a high level of efficacy of the SGVS when inoculated via the IM route than the oral route. The strain was less cytotoxic with reduced cytotoxicity on chicken macrophages and was DIVA capable with minimum reactivity of immunized serum with purified SG lipopolysaccharides. The challenge study could generate 70% protection in chicken for SGVS, whereas no birds were protected in the PBS challenged group. The protection levels were evident in histopathological assessment of spleen and liver specimens and also the external appearance of the spleen with reduced lesions on immunized groups. Further experiments may be warranted to dose and route optimization for further increase in the protection level derived by present SGVS.

Brucella melitensis Wzm/Wzt System: Changes in the Bacterial Envelope Lead to Improved Rev1Δwzm Vaccine Properties

The lipopolysaccharide (LPS) O-polysaccharide (O-PS) is the main virulence factor in Brucella. After synthesis in the cytoplasmic membrane, O-PS is exported to the periplasm by the Wzm/Wzt system, where it is assembled into a LPS. This translocation also engages a bactoprenol carrier required for further biosynthesis pathways, such as cell wall biogenesis. Targeting O-PS export by blockage holds great potential for vaccine development, but little is known about the biological implications of each Wzm/Wzt moiety. To improve this knowledge and to elucidate its potential application as a vaccine, we constructed and studied wzm/wzt single- and double-deletion mutants, using the attenuated strain Brucella melitensis Rev1 as the parental strain. This allowed us to describe the composition of Brucella peptidoglycan for the first time. We observed that these mutants lack external O-PS yet trigger changes in genetic transcription and in phenotypic properties associated with the outer membrane and cell wall. The three mutants are highly attenuated; unexpectedly, Rev1Δwzm also excels as an immunogenic and effective vaccine against B. melitensis and Brucella ovis in mice, revealing that low persistence is not at odds with efficacy. Rev1Δwzm is attenuated in BeWo trophoblasts, does not infect mouse placentas, and is safe in pregnant ewes. Overall, these attributes and the minimal serological interference induced in sheep make Rev1Δwzm a highly promising vaccine candidate.

Safety and protective efficacy of Salmonella Pullorum spiC and rfaH deletion rough mutant as a live attenuated DIVA vaccine candidate

Salmonella enterica serovar Pullorum (S. Pullorum) causes pullorum disease (PD), which is an acute systemic disease, in chickens, and leads to serious economic losses in many developing countries because of its high morbidity and mortality rate in young chicks. The live-attenuated vaccine is considered to be an effective measure to control the Salmonella infection. In addition, the DIVA (differentiation of infected and vaccinated animals) feature without the interference of serological monitoring of Salmonella infection is an important consideration in the development of the Salmonella vaccine. In this study, we evaluated the immunogenicity and protective efficacy of a S. Pullorum rough mutant S06004ΔspiCΔrfaH as a live attenuated DIVA vaccine candidate in chickens. The S06004ΔspiCΔrfaH exhibited a significant rough lipopolysaccharides (LPS) phenotype which was agglutinated with the acriflavine, not with the O₉ mono antibody. Compared to the wild-type, 50% lethal dose (LD₅₀) of the rough mutant increased 100-fold confirmed its attenuation. The mutant strain also showed a decreased bacterial colonization in the spleen and liver. The immunization with the mutant strain had no effect on the body weight and no tissue lesions were observed in the liver and spleen. The high level of the S. Pullorum-specific IgG titers in the serum indicated that significant humoral immune responses were induced in the immunization group. The cellular immune responses were also elicited from the analysis of lymphocyte proliferation and expression of cytokines in the spleen. In addition, the S06004ΔspiCΔrfaH immunized group exhibited a negative response for the serological test, while the wild-type S06004 infection group was strongly positive for the serological test showing a DIVA capability. The survival rates in the vaccinated chickens were 87% after intramuscular challenge with wild-type S. Pullorum, while the survival rates were 20% in the control groups. Overall, these results have demonstrated that the rough mutant S06004ΔspiCΔrfaH strain can be developed as an efficient live attenuated DIVA vaccine candidate to control the systemic S. Pullorum infection without the interference of salmonellosis monitoring program in poultry.

Evaluation of Safety and Protective Efficacy of a waaJ and spiC Double Deletion Korean Epidemic Strain of Salmonella enterica Serovar Gallinarum

With an aim to develop a highly attenuated and strongly immunogenic distinguishable vaccine candidate, a waaJ (a gene involved in the synthesis of lipopolysaccharide) and spiC (a virulence gene) double deletion Korean epidemic strain of S. enterica ser. Gallinarum (SG005) was constructed. Our results showed that the growth and biochemical characteristics were not altered by this double deletion. The double deletion strain contained dual markers. One was a bacteriological marker (rough phenotype) and the other was a serological marker helping distinguish infected chickens from vaccinated chickens. The double deletion strain showed good genetic stability and reduced resistance to environmental stresses in vitro; furthermore, it was extremely safe and highly avirulent in broilers. Single intramuscular or oral immunization of 7-day-old broilers with the double deletion strain could stimulate the body to produce antibody levels similar to the conventional vaccine strain SG9R. In addition, against a lethal wild-type challenge, it conferred effective protection that was comparable to that seen in the group vaccinated with SG9R. In conclusion, this double deletion strain may be an effective vaccine candidate for controlling S. enterica ser. Gallinarum infection in broilers.

Efficacy of a nanoparticle vaccine administered in-ovo against Salmonella in broilers

Salmonella is a zoonotic pathogen that persists in poultry. Salmonella vaccines that can be delivered in-ovo can be cost-effective and can decrease Salmonella load in poultry. This study evaluates the efficacy of a Salmonella chitosan-nanoparticle (CNP) vaccine, administered in-ovo, in broilers. CNP vaccine was synthesized with Salmonella Enteritidis (SE) outer-membrane-proteins (OMPs) and flagellin proteins. At embryonic-d18, one-hundred-thirty-six eggs were injected with 200μl PBS or 1000μg CNP into the amniotic cavity. At d1-of-age, 132 chicks were allocated in 6 pens/treatment with 11 chicks/pen. At d7, birds were orally challenged with 1×109 CFU/bird SE. At d1, 8h-post-challenge, d14, and d21, serum anti-SE-OMPs IgY were analyzed. At d14 and d21, cloacal swabs and bile anti-SE-OMPs IgA, CD4+/CD8+-T-cell ratios, and ceca SE loads were analyzed. At d21, cecal tonsil IL-1β, IL-10, and iNOS mRNA were analyzed. Body-weight-gain (BWG) and feed-conversion-ratio (FCR) were recorded weekly. Data were analyzed by Student's t-test at P<0.05. There were no significant differences in BWG or FCR between vaccinated birds compared to control. At d1, CNP-vaccinated birds had 5.62% greater levels (P<0.05) of anti-SE-OMPs IgY, compared to control. At 8h-post-challenge, CNP-vaccinated birds had 6.39% greater levels (P<0.05) of anti-SE-OMPs IgY, compared to control. At 2wk-post-challenge, CNP-vaccinated birds had 7.34% lower levels (P<0.05) of anti-SE-OMPs IgY, compared to control. At 1wk-post-challenge, CNP-vaccinated birds had 15.30% greater levels (P<0.05) of bile anti-SE-OMPs IgA, compared to control. At d14 and d21, CNP-vaccinated birds had 0.62 and 0.85 Log10 CFU/g, decreased SE ceca load (P<0.05), respectively, compared to control. There were no significant differences in CD4+/CD8+-T-cell ratios between vaccinated birds compared to control. There were no significant differences in IL-1β, IL-10, iNOS mRNA between vaccinated birds compared to control. Findings demonstrate that the in-ovo administration of CNP vaccine can induce an antigen-specific immune response against SE and can decrease SE cecal load in broilers.

Salmonella Pullorum spiC mutant is a desirable LASV candidate with proper virulence, high immune protection and easy-to-use oral administration

Live attenuated Salmonellavaccine (LASV) is considered to be an effective contributory measure during the control of Salmonella infection. A Salmonella Pullorum spiC mutant was evaluated comprehensively as a LASV candidate (LASV-p) for broilers in terms of safety and immunogenicity. LASV-p was adminstered to 3-day broilers by intramuscular injection. The LD₅₀ increased 126 fold, and no tissue lesions were observed in the liver, spleen and cecum, in comparison with the control group inoculated with PBS and a passive group by wild-type Salmonella. Growth rates of all broilers were normal and not affected. LASV-p persisted in vivo until 21 days in liver, 28 days in spleen and 35 days in feces, and induced high levels of humoral IgG and mucosal IgA. Cellular immunity was also stimulated in the form of antigen-specific lymphocyte proliferation and higher counts of CD3⁺CD8⁺ T cells and increased expression of mRNA of Th1 cytokines, IFN-γ and IL-2, in the early stage, and Th2 cytokines, IL-4 and IL-10, in the later stages. LASV-p provided at least 90% immuneprotection against a wild-type Salmonella Pullorum and cross-protection in different degree against other Salmonella searovars. Oral vaccine could also offer high immune protection of 87.5%. These results indicated that LASV-p vaccine candidate had a high level of safety and immune protection and it might be developed as a novel easy-to-use oral vaccine to improve poultry health in the future.

Immunogenicity and duration of immunity of the polyvalent vaccine against chicken salmonellosis

Poultry salmonellosis causes serious economic damage and must be prevented by disinfection, zoohygienic measures or by vaccination. To develop a new polyvalent vaccine against poultry salmonellosis, we used bacterial strains of Salmonella enteritidis, S. typhimurium and S. gallinarum. Antigenic and immunogenic efficacy of the vaccine was tested on specific-pathogen free chickens, which were divided into five groups of 10 birds in each group and were vaccinated intramuscularly at 8 and 12 weeks: group A (non-immunized control), group B (S. enteritidis mono-vaccine), group C (S. typhimurium mono-vaccine), group D (S. gallinarum mono-vaccine) and group E (trivalent vaccine Polimun Salmo). None of the immunized birds showed such adverse reactions as abnormal behaviour, mortality or signs of anorexia, depression or diarrhea. Two weeks after the revaccination, 5 birds in each group were challenged by watering 3 cm3 of working suspensions of S. gallinarum, S. typhimurium and S. enteritidis control strains at a concentration of 1 × 109 CFU. 72 h after the challenge, faeces were collected from all chickens in each group to identify Salmonella excretion with faeces, and the chickens were euthanized. Significant protection against the virulent challenge was observed in all immunized groups based on mortality and post-mortem lesions compared with the non-immunized control group. Blood samples were selected weekly from 5 chickens of each group for 184 days. The antigenic efficacy of the vaccines was studied by reaction of haemagglutination in the obtained serum. The potent antigen-specific response to lymphocyte activation found in all immunized groups indicated the induction of immune responses. Overall, the results showed that persistent immunity is formed in 4 weeks after the revaccination and lasts for a productive period. Immune response of chickens on day 184 after vaccination with Polimun Salmo was 1: 647, indicating that the developed polyvalent vaccine against common serovars of S. enterica in poultry is effective and immunogenic and can be further used in field studies.

Temporal dynamics of innate and adaptive immune responses in broiler birds to oral delivered chitosan nanoparticle-based Salmonella subunit antigens

Salmonella enterica serovar Enteritidis (S. Enteritidis, SE) infection of poultry causes a significant risk to public health through contamination of meat and eggs. Current Salmonella vaccines have failed to provide strong mucosal immunity in the intestines to reduce Salmonella shedding and food contamination. Considering the short lifespan of broilers, an easy-to-deliver, safe and effective Salmonella vaccine is urgently needed. Our goal in this study was to demonstrate the ability of chitosan nanoparticle (CNP) vaccine delivery platform in activating immune response to Salmonella antigens in broilers inoculated orally. In an initial study, soluble whole antigen of SE entrapped in CNP was inoculated but the specific immune responses were poor. Therefore, the CNP entrapped immunogenic outer membrane proteins (OMP) and flagellin (FLA) of SE and surface conjugated with FLA [CNP-(OMP + FLA)] was developed. In broilers inoculated orally with CNP-(OMP + FLA) formulation once or twice, we monitored the temporal expression of innate immune molecules and antigen specific lymphocyte proliferation. In the cecal tonsils of CNP-(OMP + FLA) inoculated birds, we observed enhanced expression of mRNA coding Toll-like receptors (TLRs)- 1, 4, 5, and 7, especially at dpv 21. In addition, both OMP and FLA specific lymphocytes proliferation at dpv 7 and 21 by CNP-(OMP + FLA) were enhanced in the spleen. In conclusion, CNP-(OMP + FLA) formulation augmented both innate and lymphocyte responses in orally inoculated broilers. Further studies are needed to determine the candidate subunit CNP vaccine's efficacy in a challenge trial.

Evaluation of the Safety and Protection Efficacy of spiC and nmpC or rfaL Deletion Mutants of Salmonella Enteritidis as Live Vaccine Candidates for Poultry Non-Typhoidal Salmonellosis

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a host-ranged pathogen that can infect both animals and humans. Poultry and poultry products are the main carriers of S. Enteritidis, which can be transmitted to humans through the food chain. To eradicate the prevalence of S. Enteritidis in poultry farms, it is necessary to develop novel vaccines against the pathogen. In this study, we constructed two vaccine candidates, CZ14-1∆spiC∆nmpC and CZ14-1∆spiC∆rfaL, and evaluated their protective efficacy. Both mutant strains were much less virulent than the parental strain, as determined by the 50% lethal dose (LD50) for three-day-old specific-pathogen free (SPF) White Leghorns and Hyline White chickens. Immunization with the mutant candidates induced highly specific humoral immune responses and expression of cytokines IFN-γ, IL-1β, and IL-6. In addition, the mutant strains were found to be persistent for almost three weeks post-infection. The survival percentages of chickens immunized with CZ14-1∆spiC∆nmpC and CZ14-1∆spiC∆rfaL reached 80% and 75%, respectively, after challenge with the parental strain. Overall, these results demonstrate that the two mutant strains can be developed as live attenuated vaccines.

Controversy Surrounding the Function of SpiC Protein in Salmonella: An Overview

Salmonella is an important pathogenic microorganism that can infect humans and animals and has been studied globally as a model microorganism for its pathogenesis. The SpiC protein of T3SS2 is a significant factor that has been studied for almost 20 years, but to date, the function/effect of SpiC in the pathogenesis of Salmonella has not been completely understood. There is controversy over the functions of SpiC protein in the literature. Thus, an overview of the literature on SpiC protein is provided here which highlights expression features of SpiC protein and its various functions and effect.

Induction of arthritis in chickens by infection with novel virulent Salmonella Pullorum strains

Salmonella enterica subsp. enterica serovar Gallinarum biovar Pullorum (Salmonella Pullorum) is a host-specific serovar causing systemic infection with high mortality in young chicks. Pullorum disease is characterized by white diarrhea. However, arthritis has become increasingly frequent recently, particularly in southern China. The aim of the present study was to determine the pathogenesis and arthritis induction of new Salmonella Pullorum isolates. We isolated and identified five Salmonella Pullorum strains from broilers with bacterial arthritis and lameness in a commercial poultry farm. Four of five isolates were resistant to at least three classes of antibiotics and were defined as multidrug-resistant Salmonella Pullorum. All isolates had the same CRISPR sequence type and belonged to a single major cluster. The isolates exhibited high capability of biofilm formation, which may facilitate their dispersal and survival in hostile habitats, and showed high virulence based on embryo lethality and inoculation of newly hatched chicks. Tissue distribution analysis confirmed that SP1621 was more adapted to colonize the joint when compared to the white diarrhoea-causing Salmonella Pullorum reference strain S06004. Reproducible arthritis and typical joint lesions were observed in SP1621-infected chicks, and histopathological examination showed necrotic synovitis and cartilage tissue hyperplasia of the joint. Koch's postulates were confirmed when the novel Salmonella Pullorum strain was re-isolated from the joint tissues of experimentally inoculated chicks. These novel Salmonella Pullorum isolates have unique ability to induce arthritis in chickens, representing expanded pathogenic diversity in China. These results suggest the need for strict control strategies and new vaccines to prevent the disease.

Vaccine development targeting lipopolysaccharide structure modification

Vaccines are one of the most important methods for preventing infectious disease. Structural modification of lipopolysaccharide (LPS) provides a strategy for the development of live attenuated vaccines, either by altering the immunogenicity or by attenuating virulence of the bacteria. This review summarizes various approaches that utilize LPS mutants as whole-cell vaccines.