Screening of lipid-A related genes and development of low-endotoxicity live-attenuated Salmonella gallinarum by arnT deletion that elicits immune responses and protection against fowl typhoid in chickens

In the present study, lipid-A gene mutants of Salmonella gallinarum (SG) were screened, and the arnT mutant exhibited optimal acidic and oxidative-stress and macrophage-survival. Modifying lipid-A by arnT-deletion resulted in significantly reduced endotoxicity, virulence, and mortality. Therefore, the arnT-deleted vaccine-candidate strain JOL2841 was constructed and demonstrated to be safe due to appropriate clearance by the chicken immune system. The reduced-endotoxicity of JOL2841 was evident from the downregulation of TNFα and IL-1β inflammatory cytokines, no inflammatory signs in organ gross-examination, and histopathological analysis. The IgY and IgA antibody titres, CD4, and CD8 T-cell population improvements, and IL-4, IL-2, and INFγ expression decipher the profound Th2 and Th1 immunogenicity. Consequently, JOL2841 exhibited prominent protection against wild-type SG challenge, as revealed by organ pathogen-load determination, organ gross-examination, and histopathological examination. Overall, the study represented the first report of arnT deficient SG resulted in negligible endotoxicity, low-virulence, safety and coordinated elicitation of humoral and cell-mediated immune response in chickens.

Salmonella gallinarum strains from outbreaks of fowl typhoid fever in Southern Africa closely related to SG9R vaccines

Introduction

Salmonella enterica subspecies enterica serovar Gallinarum biovar Gallinarum (SG) is associated with fowl typhoid fever, and the attenuated rough strain SG9R is widely used as a vaccine in many regions. Reversion to virulence of vaccine strains was suspected as the cause during recent fowl typhoid fever outbreaks in poultry in South Africa and Eswatini.

Methods

To compare nine field isolates with global wild-type SG9 strains and the two commercial SG9R vaccines in use, Nobilis^® SG9R and Cevac^®-SG, we used whole-genome comparison with single-nucleotide polymorphism (SNP) detection.

Results

SNP phylogenic analysis showed that all the southern African field isolates were more closely related to the vaccine strains than wild-type SG9 strains. Furthermore, SNPs in the pyruvate dehydrogenase (aceE) and/or lipopolysaccharide 1,2-glucosyltransferase (rfaJ) genes, which are known markers of attenuation, were found in four of the field isolates along with intact spv, SPI-1, and SPI-2 gene clusters, providing conclusive evidence that these four isolates were originally vaccine strains that reverted to virulence. Five other field isolates lacked the SG9R attenuation markers, but variant analysis identified an SNP in the yihX gene, insertions in the ybjX and hydH genes, and deletions in the ftsK and sadA genes that were shared between the field isolates and vaccine strains but absent in wild-type SG9, indicating that these field isolates were also likely revertant vaccines.

Discussion

Overall, this study highlights different mechanisms of reversion of two commercial vaccines, where virulence caused by field isolates closely related to the Nobilis^® SG9R vaccine was associated with the restoration of intact virulence gene clusters, and those derived from the Cevac^®-SG vaccine were characterized by point mutations resulting in restored aceE and rfaJ genes. A possible new marker of attenuation was identified as a point mutation in the yihX gene, as well as four new candidate genes that could potentially be used to distinguish current vaccine strains from wild-type strains using PCR assays.

SGP-C: A Broad Host Range Temperate Bacteriophage; Against Salmonella gallinarum

Salmonella gallinarum is a poultry restricted-pathogen causing fowl-typhoid disease in adult birds with mortality rates up-to 80% and exhibit resistance against commonly used antibiotics. In this current study, a temperate broad host range bacteriophage SGP-C was isolated against S. gallinarum from poultry digesta. It showed infection ability in all the 15 tested field strains of S. gallinarum. The SGP-C phage produced circular, turbid plaques with alternate rings. Its optimum activity was observed at pH 7.0 and 37-42°C, with a latent period of 45 min and burst size of 187 virions/bacterial cell. The SGP-C lysogens, SGPC-L5 and SGPC-L6 exhibited super-infection immunity against the same phage, an already reported feature of lysogens. A virulence index of 0.5 and 0.001 as MV50 of SGP-C suggests its moderate virulence. The genome of SGP-C found circular double stranded DNA of 42 Kbp with 50.04% GC content, which encodes 63 ORFs. The presence of repressor gene at ORF49, and absence of tRNA sequence in SGP-C genome indicates its lysogenic nature. Furthermore, from NGS analysis of lysogens we propose that SGP-C genome might exist either as an episome, or both as integrated and temporary episome in the host cell and warrants further studies. Phylogenetic analysis revealed its similarity with Salmonella temperate phages belonging to family Siphoviridae. The encoded proteins by SGP-C genome have not showed homology with any known toxin and virulence factor. Although plenty of lytic bacteriophages against this pathogen are already reported, to our knowledge SGP-C is the first lysogenic phage against S. gallinarum reported so far.

Evidence of vector borne transmission of Salmonella enterica enterica serovar Gallinarum and fowl typhoid disease mediated by the poultry red mite, Dermanyssus gallinae (De Geer, 1778)

BACKGROUND

The poultry red mite Dermanyssus gallinae (De Geer, 1778) is a major ectoparasite of poultry. Infestations are found in most laying hen farms in Europe, and breeder flocks have also been reported to be affected. Mite infestation has detrimental effects on animal welfare, it causes significant economic losses, and, additionally, D. gallinae is often considered as a vector for pathogens. Despite suspicion of a close relationship between the poultry red mite and Salmonella enterica enterica serovar Gallinarum biovar Gallinarum (serovar Gallinarum), the causative agent of fowl typhoid disease (FT), there has been no definitive proof of mite-mediated transmission. Therefore, an investigation was conducted to determine if D. gallinae-mediated transmission of serovar Gallinarum could be demonstrated among four different hen groups.

METHODS

Two groups of 8 hens (A and B) were experimentally infected with serovar Gallinarum in two isolators. After 7 days, when birds showed signs of FT, about 25,000 mites were introduced. After 3 days, mites were harvested and used to infest two other hen groups of 8 (C and D), in two separate isolators. The health status of hens was constantly monitored; detection and quantification of serovar Gallinarum were performed by PCR and qPCR from mites and organs of dead hens. The maximum likelihood estimation of the infection rate and mite vectorial capacity were calculated.

RESULTS

Clinical disease was observed in groups infected with serovar Gallinarum (A and B) and in hens of groups C and D infested with mites harvested from the isolators containing groups A and B. In all four groups, serovar Gallinarum was detected from liver, spleen, ovary, and cecum of hens, thus confirming the diagnosis of FT. Mite analysis demonstrated the presence of the pathogen, with an estimated infection rate ranging between 13.72 and 55.21 infected per thousand mites. Vectorial capacity was estimated to be 73.79.

CONCLUSIONS

Mites harvested from birds infected with serovar Gallinarum were shown to carry the mite, and then to transfer serovar Gallinarum to isolated groups of pathogen-free birds that subsequently showed signs of FT. Mite vectorial capacity was high, demonstrating that D. gallinae should be considered an effective vector of FT.

iTRAQ-based quantitative proteomics analysis reveals inhibitory mechanismsof the antimicrobial peptide MDAP-2 against Salmonella gallinarum

MDAP-2 is a new AMP with high inhibitory activity on Salmonella gallinarum, which may be developed as an antimicrobial agent in the agricultural industry and food preservation. To investigate the underlying the action mechanism of MDAP-2 on Salmonella gallinarum, impacts of MDAP-2 on the growth curve and bacterial morphology of Salmonella gallinarum were studied. iTRAQ-based proteomics analysis was also performed on proteins extracted from treated and untreated Salmonella gallinarum cells. The differentially expressed proteins were then analyzed using the KEGG and GO databases. Finally, the function of some differentially expressed proteins was verified. The results showed that 150 proteins (41 up-regulated and 109 down-regulated) were found differentially expressed (fold > 1.8, p⟨0.05). The results indi- cate that MDAP-2 kills Salmonella gallinarum mainly through two mechanisms: (i) direct inhibi- tion of cell wall/ membrane/ envelope biogenesis, energy production/ conversion, carbohydrate transport/ metabolism, and DNA transcription/ translation through regulation of special protein levels; (ii) indirect effects on the same pathway through the accumulation of Reactive oxygen species (O2 ▪-, H2O2 and OH▪-).

Effect of Dietary Bacillus Subtilis C14 and RX7 Strains on Growth Performance, Blood Parameter, and Intestinal Microbiota in Broiler Chickens Challenged with Salmonella Gallinarum

Sixty broilers (initially 1.6 kg and 35 d-old) were used to determine the effect of Bacillus subtilis C14 and RX7 strains on growth performance, blood parameter, and intestinal microbiota in response to experimental challenge with Salmonell gallinarum. Broilers were distributed to 4 treatment groups include: C1 (control group; no challenge, no B. subtilis), C2 (Salmonella-challenged group; S. gallinarum 10⁸ cfu/bird), T1 (C2+supplemented with of B. subtilis C14 (1.0×10⁹ cfu/g) at 0.1% in diet) and T2 (C2+supplemented with of B. subtilis RX7 (1.0×10⁹ cfu/g) at 0.1% in diet). Results indicated that inclusion of B. subtilis (T1, T2) in the diet increased (P<0.05) the weight gain and feed intake, and improved feed conversion of challenged broilers compared with no B. subtilis supplementation diet (C2). Improvements (P<0.05) in the immunoglobulin A concentration were observed by the addition of B. subtilis compared with C2 treatment, whereas tumor necrosis factor-α was decreased (P<0.05). Latobacillus number in small and large intestines was higher (P<0.05) by B. subtilis additon than C2 treatment but Salmonella numbers were lower (P<0.05). The results suggested that dietary supplementation of B. subtilis C14 and RX7 improved the growth performance, and affected the blood profiles and intestinal microbiota of broilers against S. gallinarum infection. Therefore, B. subtilis C14 and RX7 may have beneficial effects, in relieving the stress of broilers infected with S. gallinarum.

Safety and protective efficacy of a spiC and crp deletion mutant of Salmonella gallinarum as a live attenuated vaccine for fowl typhoid

With an aim to develop a safe, immunogenic fowl typhoid (FT) vaccine, the safety and efficacy of 1009ΔspiCΔcrp, a spiC and crp deletion mutant of Salmonella gallinarum, were evaluated in chickens. Three-day-old chickens were intramuscularly immunized with 1009ΔspiCΔcrp (1×10(7)CFU) and boosted 7days later (at 10-days old) with the same dose and via the same route (vaccinated group). The vaccinated group showed no clinical symptoms and no differences in body weight compared to the unvaccinated control group. 1009ΔspiCΔcrp bacteria colonized and persisted in the liver and spleen of vaccinated chickens for >14days, and significant specific humoral and cellular immune responses were induced. Vaccinated chickens were challenged with S. gallinarum strain SG9 at 21days post-immunization (24-day-old chickens), and efficient protection was observed based on the mortality and clinical symptoms, as compared to those in the control group. These results demonstrate that 1009ΔspiCΔcrp can be used as a live attenuated vaccine.

Probiotics in Salmonella-challenged Hy-Line brown layers

A total of 192 Hy-Line Brown 40-week-old Salmonella-free layers were randomly assigned to 4 dietary treatments in a 5-wk experiment to test the efficacy of probiotics on egg production and quality, excreta and intestinal microbiota of laying birds challenged with Salmonella gallinarum. Dietary treatment comprised of (1) NC: ; basal diet, negative control, (2) PC: ; basal diet + oral S. gallinarum administration, positive control, (3) T1: ; basal diet + 0.1% Bacillus subtilis RX7 1 × 10(9) cfu/g + S. gallinarum administration and (4) T2: ; basal diet + 0.1% Bacillus methylotrophicus C14 1 × 10(9) cfu/g + S. gallinarum administration. All birds (n = 144) except NC were orally challenged with 1 ml suspension of 10(8) cfu/mL S. gallinarum KVCC BA 0700722 once at d 28 after the initiation of experiment. The egg production improved in post Salmonella-challenged birds whereas egg equality was improved during pre-challenge in probiotic supplemented birds compared to NC and PC. The Salmonella counts in the excreta were lower (P < 0.05) in T1 and T2 than PC at the end of the experiment whereas the Lactobacillus counts in the excreta were higher (P < 0.05) in T1 compared with NC. The Escherichia coli counts in excreta were numerically lower in T1 and T2 than PC. In the small and large intestine, there was slight increase in Lactobacillus counts in T2 compared with PC. The Salmonella counts in small and large intestine tended to be lower in T1 and T2 as compared with PC. However, Salmonella counts in challenged birds not supplemented with probiotics were significantly higher than non-challenged birds.

Identification of Isolated Salmonella enterica Serotype gallinarum Biotype Pullorum and Gallinarum by PCR-RFLP

Background:

Salmonella spp. is the major bacterial pathogen in poultry and is responsible for significant economic losses of the poultry industry in many parts of the world. Among Salmonella spp., Salmonellagallinarum and Salmonella.pullorum are the most common causative agents of chicken salmonellosis resulting in high mortality and morbidity.

Objectives:

The aim of this study was to identify S. gallinarum and S. pullorum by using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

Materials and Methods:

In this study, 13 samples of Salmonella, isolated from local poultry, were obtained from Razi Type Culture Collection (RTCC). For the PCR-RFLP method based on the fliC gene, extracted DNA was used as a template for amplifying of the fliC gene (197bp) using specific primers. PCR products were subjected to digestion using Hinp1I restriction endonuclease.

Results:

For the PCR, 197 bp fliC fragment was amplified from all 13 isolates. Ten out of 13 were S.gallinarum and the other three were S. pullorum. As part of the PCR-RFLP, two fragments were obtained (82 bp and 115 bp) for all S.gallinarum, whereas no digestion was observed in S. pullorum, and 197 bp fragment was seen.

Conclusions:

PCR-RFLP with fliC gene and Hinp1I endonuclease were successfully applied to differentiate the two biotypes. The results suggested that this technique could be effective in detecting S. gallinarum and S. pullorum.