Characteristics of systemic infection and host responses in chickens experimentally infected with Salmonella enterica serovar Gallinarum biovar Gallinarum

Synthesis and pharmacological evaluation of Andrographolide and Ajwain as promising alternatives to antibiotics for treating Salmonella gallinarum infection in chicken

The emergence of antibiotic resistance in pathogenic bacteria, including Salmonella gallinarum, poses a significant challenge to poultry health and food safety. In response, alternative strategies are urgently needed to mitigate bacterial infections without exacerbating antibiotic resistance. Phytoremediation, a sustainable and environmentally friendly approach, harnesses the natural detoxification capabilities of plants to remediate contaminants. This study explores the potential of combined phytoremediation using Andrographolide, derived from Andrographis paniculata, and Ajwain derived from Trachyspermum ammi as promising alternatives to antibiotics for treating Salmonella gallinarum infection in poultry. Andrographolide, known for its potent antimicrobial properties, exhibits inhibitory effects while Ajwain, rich in bioactive compounds, possesses antimicrobial and immunomodulatory properties. By leveraging their combined phytoremediation potential, Andrographolide and Ajwain offer a multifaceted approach to combat Salmonella gallinarum within the poultry environment. The study employed a rigorous experimental design, including in vitro assessments of antimicrobial susceptibility, cytotoxicity, and optimal concentration determination. Following this, in vivo experiments were conducted using a chicken model infected with Salmonella gallinarum. Results demonstrated that the selected combinations effectively reduced mortality rates, alleviated clinical symptoms, and mitigated gross pathological signs associated with Salmonella infection. Gene expression studies indicated a downregulation of proinflammatory cytokines, underscoring potential implications of a combined phytoremediation strategy as an innovative and sustainable solution to address Salmonella gallinarum infections in poultry production systems.

Safety and efficacy of 9R live attenuated vaccine against fowl typhoid in partridge's species

Fowl typhoid is a significant avian disease worldwide affecting mainly chickens, turkeys and other bird species, such as partridges. In Morocco, the disease causes a high mortality rate in farmed partridges. Vaccination of partridges is a priority to preserve the breed however; the vaccine has never been evaluated in this species. The study was conducted to assess safety and efficacy of a locally produced Salmonella 9R live vaccine in partridges. Groups of vaccinated partridges received the vaccine at 6 weeks of age, followed by a second injection 6 weeks after. The challenge test was performed at 14 weeks with Salmonella gallinarum MSG1 virulent strain. The challenge demonstrated 65 % protection in vaccinated challenged partridges, with a reduction in organ invasion compared to unvaccinated control birds, which exhibited 70,6 % mortality. The live attenuated 9R vaccine, could be safely used to reduce flock losses and contribute to the reduction of infection.

Critical Involvement of the Thioredoxin Reductase Gene (trxB) in Salmonella Gallinarum-Induced Systemic Infection in Chickens

Salmonella enterica serovar Gallinarum biovar Gallinarum (SG) causes fowl typhoid, a notifiable infectious disease in poultry. However, the pathogenic mechanism of SG-induced systemic infection in chickens remains unclear. Thioredoxin reductase (TrxB) is a redox protein crucial for regulating various enzyme activities in Salmonella serovar, but the role in SG-induced chicken systemic infection has yet to be determined. Here, we constructed a mutant SG strain lacking the trxB gene (trxB::Cm) and used chicken embryo inoculation and chicken oral infection to investigate the role of trxB gene in the pathogenicity of SG. Our results showed that trxB::Cm exhibited no apparent differences in colony morphology and growth conditions but exhibited reduced tolerance to H2O2 and increased resistance to bile acids. In the chicken embryo inoculation model, there was no significant difference in the pathogenicity of trxB::Cm and wild-type (WT) strains. In the chicken oral infection, the WT-infected group exhibited typical clinical symptoms of fowl typhoid, with complete mortality between days 6 and 9 post infection. In contrast, the trxB::Cm group showed a 100% survival rate, with no apparent clinical symptoms or pathological changes observed. The viable bacterial counts in the liver and spleen of the trxB::Cm-infected group were significantly reduced, accompanied by decreased expression of cytokines and chemokines (IL-1β, IL-6, IL-12, CXCLi1, TNF-α, and IFN-γ), which were significantly lower than those in the WT group. These results show that the pathogenicity of the trxB-deficient strain was significantly attenuated, indicating that the trxB gene is a crucial virulence factor in SG-induced systemic infection in chickens, suggesting that trxB may become a potentially effective target for controlling and preventing SG infection in chickens.

Salmonella pathogenicity island-14 is a critical virulence factor responsible for systemic infection in chickens caused by Salmonella gallinarum

Salmonella enterica serovar Gallinarum (S. gallinarum) is an important host-specific pathogen that causes fowl typhoid, a severe systemic, septicemic, and fatal infection, in chickens. S. gallinarum causes high morbidity and mortality in chickens and poses a significant burden and economic losses to the poultry industry in many developing countries. However, the virulence factors and mechanisms of S. gallinarum-induced systemic infection in chickens remain poorly understood. In this study, we constructed a Salmonella pathogenicity island-14 (SPI-14) mutant strain (mSPI-14) of S. gallinarum and evaluated the pathogenicity of mSPI-14 in the chicken systemic infection model. The mSPI-14 exhibited the same level of bacterial growth and morphological characteristics but significantly reduced resistance to bile acids compared with the wild-type (WT) strain in vitro. The virulence of mSPI-14 was significantly attenuated in the chicken oral infection model in vivo. Chickens infected with WT showed typical clinical symptoms of fowl typhoid, with all birds succumbing to the infection within 6 to 9 days post-inoculation, and substantial increases in bacterial counts and significant pathological changes in the liver and spleen were observed. In contrast, all mSPI-14-infected chickens survived, the bacterial counts in the organs were significantly lower, and no significant pathological changes were observed in the liver and spleen. The expression of interleukin (IL)-1β, IL-12, CXCLi1, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ in the liver of mSPI-14-infected chickens were significantly lower than those in the WT-infected chickens. These results indicate that SPI-14 is a crucial virulence factor in systemic infection of chickens, and avirulent mSPI-14 could be used to develop a new attenuated live vaccine to prevent S. gallinarum infection in chickens.

Potential of cinnamaldehyde essential oil as a possible antimicrobial against fowl typhoid in layers

Fowl typhoid (FT) is an economically significant bacterial disease of layers leading to a drastic drop in egg production. Due to increased public health concerns about antibiotics in poultry feed, a search for new safe antimicrobials for treating fowl typhoid is crucial. The antimicrobial effect of cinnamaldehyde essential oil (CnEO) against fowl typhoid in layers was investigated in this experiment. The 60-week-old BV300-layer birds (n = 100) were divided into five groups: the non-challenged control group A, only cinnamaldehyde-treated group B (CnEO @ 1:8000 dilutions through drinking water for 60 days), the challenged group C, challenged plus cinnamaldehyde therapy group D (CnEO @ 1:8000 dilutions through drinking water from 16 to 30 dpi), and challenged plus antibiotic therapy group E (chloramphenicol @ 1 gm/5lit through drinking water from 16 to 30 dpi). Hens from all challenged groups were challenged with Salmonella Gallinarum (VTCCBAA588) @ 1 × 10⁸ CFU/ml orally. Various parameters such as clinical signs, mortality, egg production and egg weight, colony-forming unit (CFU) count of cecal content, eggshell surface, and egg yolk were evaluated all through 60 days of an experimental trial. Results indicated that, in the case of the cinnamaldehyde therapeutic group, there was a significant improvement in egg production, mild clinical signs, lower feed conversion ratio (FCR), and a significantly lower bacterial count in ceca and on the eggshell surface compared to the control challenge group. Thus, CnEO @ 1:8000 dilutions through drinking water can be a potential antimicrobial for controlling fowl typhoid.

Highly different effects of phage therapy and antibiotic therapy on immunological responses of chickens infected with Salmonella enterica serovar Typhimurium

The appearance of bacteria resistant to most or even all known antibiotics has become a serious medical problem. One such promising and effective alternative form of therapy may be the use of phages, the administration of which is considered to be safe and highly effective, especially in animals with drug-resistant infections. Although there have been no reports to date suggesting that bacteriophages can cause any severe complications or adverse effects, we still know little about their interactions with animal organisms, especially in the context of the functioning of the immune system. Therefore, the aim of the present study was to compare the impact of the application of selected bacteriophages and antibiotics (enrofloxacin and colistin), commonly used in veterinary medicine, on immune functions in Salmonella enterica serovar Typhimurium-infected chickens. The birds were infected with S. Typhimurium and then treated with a phage cocktail (14 days), enrofloxacin (5 days), or colistin (5 days). The concentrations of a panel of pro-inflammatory cytokines (IL-1β, IL-6, IFN-γ, IL-8, and IL-12) and cytokines that reveal anti-inflammatory effects (IL-10 and IL-4), the percentage of lymphocytes, and the level of stress hormones (corticosterone and cortisol), which significantly modulate the immune responses, were determined in different variants of the experiment. The phage cocktail revealed anti-inflammatory effects when administered either 1 day after infection or 2 days after S. Typhimurium detection in feces, as measured by inhibition of the increase in levels of inflammatory response markers (IL-1β, IL-6, IFN-γ, IL-8, and IL-12). This was also confirmed by increased levels of cytokines that exert an anti-inflammatory action (IL-10 and IL-4) following phage therapy. Moreover, phages did not cause a negative effect on the number and activity of lymphocytes’ subpopulations crucial for normal immune system function. These results indicate for the first time that phage therapy not only is effective but also can be used in veterinary medicine without disturbing immune homeostasis, expressed as cytokine imbalance, disturbed percentage of key immune cell subpopulations, and stress axis hyperactivity, which were observed in our experiments as adverse effects accompanying the antibiotic therapy.

wecB Gene of Salmonella Gallinarum Plays a Critical Role in Systemic Infection of Fowl Typhoid

Salmonella enterica serovar Gallinarum (S. Gallinarum) is a host-specific pathogen causing fowl typhoid, a severe systemic infection in poultry, which leads to substantial economic losses due to high morbidity and mortality in many developing countries. However, less is known about the pathogenic characteristics and mechanism of S. Gallinarum-induced systemic infection in chickens. In this study, we deleted the S. Gallinarum UDP-N-acetylglucosamine-1-phosphate transferase gene, which contributes to the biosynthesis of enterobacterial common antigen (ECA), and studied the pathogenicity of this wecB::Cm strain in a chicken model of systemic infection. The wecB::Cm mutant strain showed comparable growth but lower resistance to bile acid and nalidixic acid than the wild-type strain in vitro. In the oral infection model of chickens, the virulence of the wecB::Cm strain was significantly attenuated in vivo. Chickens infected with wild-type strain showed typical clinical signs and pathological changes of fowl typhoid and died between 6 and 9 days post-infection, and the bacteria rapidly disseminated to systemic organs and increased in the livers and spleens. In contrast, the wecB::Cm mutant strain did not cause chicken death, there were no significant clinical changes, and the bacterial numbers in the liver and spleen of the chickens were significantly lower than those of the chickens infected with the wild-type strain. In addition, the expression of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and CXCLi1 in the livers of wecB::Cm-infected chickens was significantly lower than that of the chickens infected with the wild-type strain. Furthermore, the attenuated wecB::Cm strain could persistently colonize the liver and spleen at low levels for up to 25 days post-infection and could induce a protective immune response in the chickens. These results indicate that the wecB gene is an important virulence factor of S. Gallinarum in the chicken model of systemic infection, and the avirulent wecB::Cm mutant could possibly be used as a live-attenuated vaccine strain for controlling fowl typhoid.