Salmonella Pullorum lacking srfA is attenuated, immunogenic and protective in chickens

Salmonella Type III Secretion System Effectors

Salmonella is estimated to infect between 200 million and over 1 billion people per year. The exact number is not known, as many cases go unreported. Integral to the pathogenesis of Salmonella, as well as numerous other Gram-negative pathogens, is its type III effectors. Salmonella possesses two distinct type III secretion systems, encoded by Salmonella pathogenicity island-1 and Salmonella pathogenicity island-2. Together, they secrete at least 49 type III effectors into host cells that are collectively responsible for many of the virulence attributes of this pathogen. These virulence factors facilitate the invasion of host cells, induce and attenuate inflammation, and change the migratory properties of infected phagocytes, among other things. The effects of all type III effectors on Salmonella virulence are discussed.

Isolation, characterization, and genome sequencing analysis of a novel phage HBW-1 of Salmonella

Salmonella presents a significant threat to the health of animals and humans, especially with the rise of strains resistant to multiple drugs. This highlights the necessity for creating sustainable and efficient practical approaches to managing salmonellosis. The most recent and safest approach to combat antimicrobial resistance-associated infections is lytic bacteriophages. This study recovered a Salmonella-specific phage HBW-1 from sewage and faecal samples from commercial chicken farms in Henan, China. Transmission electron microscopy showed that the phage possesses a polyhedral head and a tailed structure characteristic of bacteriophages. The phage HBW-1 exhibited favorable stability when subjected to elevated temperatures between 30 °C and 60 °C and pH levels between 3 and 12 for 1 h. The phage genome consists of double-stranded, circular DNA with a size of 43,095 bp and a GC content of 49.54 %. Notably, phage HBW-1 contains 62 genes encoding proteins and does not contain virulence or resistance genes commonly found in bacteria. Phage spectrum analysis indicates that the phage HBW-1 is strictly a lytic, exhibiting antibacterial activity against Salmonella Pullorum (100 %, n = 11), Salmonella Typhimurium (92.86 %, n = 42) and Salmonella Enteritidis (58.97 %, n = 39). Therefore, this study suggests that phage HBW-1 holds promise as a potential alternative for prevention and control of Pullorum Disease.

Construction and evaluation of a Salmonella Paratyphi A vaccine candidate based on a poxA gene mutation

Salmonella Paratyphi A, the pathogen of paratyphoid A accounts for an obviously growing proportion of cases in many areas. Therefore, development of specific paratyphoid A vaccines is needed. In the present study, the poxA gene of Salmonella Paratyphi A, encoding the aminoacyl-tRNA synthetase, was deleted successfully by the method of lambda Red recombination system, the resulting strain, ΔpoxA was characterized in respect of growth, adhesion and invasion, virulence, immunogenicity and protective efficacy. It was found that the growth of the ΔpoxA strain was significantly delayed compared with the wild type strain, the mutant ΔpoxA was less invasive to Caco-2 BBE epithelioid cells and THP-1 macrophages than the wild type strain, strain ΔpoxA was attenuated at least 1000-fold in mice, significant immune response and efficient protection were provided by the mutant ΔpoxA after oral immunization. It is concluded that the Salmonella Paratyphi A poxA deletion mutant ΔpoxA can be used as a live oral vaccine candidate against paratyphoid A.

Salmonella Phage vB_SpuM_X5: A Novel Approach to Reducing Salmonella Biofilms with Implications for Food Safety

Salmonella, a prevalent foodborne pathogen, poses a significant social and economic strain on both food safety and public health. The application of phages in the control of foodborne pathogens represents an emerging research area. In this study, Salmonella pullorum phage vB_SpuM_X5 (phage X5) was isolated from chicken farm sewage samples. The results revealed that phage X5 is a novel Myoviridae phage. Phage X5 has adequate temperature tolerance (28 °C-60 °C), pH stability (4-12), and a broad host range of Salmonella bacteria (87.50% of tested strains). The addition of phage X5 (MOI of 100 and 1000) to milk inoculated with Salmonella reduced the number of Salmonella by 0.72 to 0.93 log10 CFU/mL and 0.66 to 1.06 log10 CFU/mL at 4 °C and 25 °C, respectively. The addition of phage X5 (MOI of 100 and 1000) to chicken breast inoculated with Salmonella reduced bacterial numbers by 1.13 to 2.42 log10 CFU/mL and 0.81 to 1.25 log10 CFU/mL at 4 °C and 25 °C, respectively. Phage X5 has bactericidal activity against Salmonella and can be used as a potential biological bacteriostatic agent to remove mature biofilms of Salmonella or for the prevention and control of Salmonella.

Ligilactobacillus salivarius XP132 with antibacterial and immunomodulatory activities inhibits horizontal and vertical transmission of Salmonella Pullorum in chickens

Probiotics are increasingly recognized for their capacity to combat pathogenic bacteria. In this study, we isolated a strain of Ligilactobacillus salivarius XP132 from the gut microbiota of healthy chickens. This strain exhibited resistance to low pH and bile salts, auto-aggregation capabilities, and the ability to co-aggregate with pathogenic Salmonella. The in vitro antibacterial activity of Ligilactobacillus salivarius XP132 was tested using an Oxford cup antibacterial test, and the results showed that Ligilactobacillus salivarius XP132 exhibited broad-spectrum antibacterial activity, with especially strong antibacterial activity against Salmonella. In animal experiments with white feather broilers and specific-pathogens-free (SPF) chickens, we orally administered 1 × 109 CFU XP132 live bacteria per chicken per day, and detected the content of Salmonella in the liver, spleen, intestinal contents, and eggs of the chickens by RT-qPCR. Oral administration of Lactobacillus salivarius XP132 group significantly reduced the levels of Salmonella in chicken liver, spleen, intestinal contents and eggs, and the oral administration of Ligilactobacillus salivarius XP132 significantly inhibited the horizontal and vertical transmission of Salmonella in SPF chickens and white-feathered broilers. After oral administration of XP132, the production of chicken serum anti-infective cytokine IFN-γ was also significantly up-regulated, thereby enhancing the host's ability to resist infection. In addition, the production of various serum inflammatory cytokines, including IL-1β, IL-6, IL-8, and TNF-α, was down-regulated, leading to significant amelioration of the inflammatory response induced by S. Pullorum in chickens. These findings suggest that Ligilactobacillus salivarius XP132 possesses potent antibacterial and immunomodulatory properties that effectively prevent both horizontal and vertical transmission of Salmonella Pullorum, highlighting its potential as a valuable tool for the prevention and control of Salmonella disease.

Accurate identification and discrimination of Salmonella enterica serovar Gallinarum biovars Gallinarum and Pullorum by a multiplex PCR based on the new genes of torT and I137_14430

Most cases of chicken salmonellosis are caused by Salmonella enterica serovar Gallinarum biovars Gallinarum and Pullorum, which lead to a significant morbidity and fatality rate. Although the conventional Kaufmann-White scheme is the reliable method for the serotyping of Salmonella, it does not distinguish between closely related biotypes like S. Pullorum and S. Gallinarum. Herein, we conducted a single one-step multiplex PCR assay that can identify and distinguish between S. Pullorum and S. Gallinarum in an accurate manner. This PCR method was based on three genes, including torT for S. Pullorum identification, I137_14430 for S. Gallinarum identification, and stn as the genus-level reference gene for Salmonella. By comparing S. Pullorum to S. Gallinarum and other serovars of Salmonella, in silico study revealed that only the former has a deletion of 126 bp-region in the carboxyl terminus of torT. The I137_14430 gene does not exist in S. Gallinarum. However, it is present in all other Salmonella serotypes. The multiplex PCR approach utilizes unique sets of primers that are intended to specifically target these three different genes. The established PCR method was capable of distinguishing between the biovars Pullorum and Gallinarum from the 29 distinct Salmonella serotypes as well as the 50 distinct pathogens that are not Salmonella, showing excellent specificity and exclusivity. The minimal amount of bacterial cells required for PCR detection was 100 CFU, while the lowest level of genomic DNA required was 27.5 pg/μL for both S. Pullorum and S. Gallinarum. After being implemented on the clinical Salmonella isolates collected from a poultry farm, the PCR test was capable of distinguishing the two biovars Pullorum and Gallinarum from the other Salmonella strains. The findings of the PCR assay were in line with those of the traditional serotyping and biochemical identification methods. This new multiplex PCR could be used as a novel tool to reinforce the clinical diagnosis and differentiation of S. Pullorum and S. Gallinarum, particularly in high-throughput screening situations, providing the opportunity for early screening of infections and, as a result, more effective management of the illness among flocks.

Contribution of prgH gene for Salmonella Pullorum to virulence and the expression of NLRP3, Caspase-1 and IL-1β in chickens

Type III secretion system 1 (T3SS1) encoded by Salmonella pathogenicity island 1 (SPI1) is associated with invasion of host cells by Salmonella, PrgH encoded by prgH gene is an important component of T3SS1. This study aimed to explore the contribution of prgH gene for Salmonella Pullorum to virulence and the expression of NLRP3, Caspase-1 and IL-1β in chickens. A prgH gene deletion mutant (C79-13ΔprgH) was firstly generated, and the result of LD₅₀ showed that deletion of prgH significantly decreased the virulence of Salmonella Pullorum in one-day-old HY-line white chickens, and the colonization also decreased in chickens after loss of prgH. Next, the expressions of NLRP3, Caspase-1, and IL-1β were detected in acute infection model of chickens by qRT-PCR and/or ELISA, respectively, and the results showed that the mutant strain C79-13ΔprgH reduced the expression levels of NLRP3, Caspase-1, and IL-1β in chickens compared to the group infected with the wild type strain C79-13. Taken together, all of these findings indicated that prgH promotes the virulence and the expression of NLRP3, Caspase-1, and IL-1β for Salmonella Pullorum in chickens.