The salmonella effector Hcp modulates infection response, and affects salmonella adhesion and egg contamination incidences in ducks

Salmonella enterica serovar Typhimurium uses T6SS to promote bacterial adaptability and enhance its survival of niches in broiler chickens

The type VI secretion system (T6SS) is a specialized protein complex in Gram-negative bacteria that delivers toxic effector molecules into target cells. However, the role of ClpV-a critical ATPase involved in T6SS assembly in Salmonella pathogenesis remains poorly understood. In this study, we investigated the contribution of ClpV to environmental stress resistance and virulence in Salmonella enterica serovar Typhimurium (S. Typhimurium). Our findings demonstrate that ClpV significantly influences the ability of S. Typhimurium strain SL1344 to with stand various stressors, including bile salts, acidic conditions, hydrogen peroxide, and ethanol. Furthermore, ClpV enhances the competitive fitness of S. Typhimurium against commensal gut bacteria. Notably, ClpV appears to play a crucial role in pathogenicity by modulating the gut environment, disrupting microbial homeostasis, and facilitating bacterial persistence in host niches. These results provide a foundation for future studies on the molecular mechanisms by which T6SS mediates gut colonization and chronic infection in S. Typhimurium.

Genomic and virulent characterization of a duck-associated Salmonella serovar Potsdam from China

Salmonella, a common zoonotic pathogen, is a significant concern for public health, particularly when it contaminates animal-borne products. The potential for Salmonella to infect duck embryos and disrupt their normal development not only causes substantial economic losses for the industry but also poses a severe threat to public health. However, there is a lack of understanding about the prevalence of Salmonella in duck embryos and their potential public health implications. Our study aims to fill this gap by providing genomic features of the antimicrobial resistance and virulence potential of Salmonella isolates from dead duck embryos using whole-genome sequencing and in silico toolkits. We also sought to assess the virulent characterization of the major serovar isolates by experimental infection of chicken and duck embryos. Our investigation of 195 duck embryo eggs led to the isolation of 40 (20.51%) Salmonella strains, with Salmonella serovar Potsdam being the most prevalent serovar. Most isolates were resistant to streptomycin (57.3%) and nalidixic acid (50%). Notably, our findings demonstrated that S. Potsdam exhibited a preference for ducks over chickens, suggesting potential host specificity. Additionally, global phylogenomic analysis, incorporating 180 global genomes, revealed a predominant association of S. Potsdam with ducks, supporting an adaptive process specific to the waterfowl. This study determined Salmonella serovars and antimicrobial resistance profiles in dead duck embryos, revealing a rare Salmonella serovar Potsdam with a potential for duck adaption.

Colonization Mediated by T6SS-ClpV Disrupts Host Gut Microbiota and Enhances Virulence of Salmonella enterica serovar Typhimurium

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a common foodborne enteric pathogen that infects humans or mammals and colonizes the intestinal tract primarily by invading the host following ingestion. Meanwhile, ClpV is a core secreted protein of the bacterial type VI secretion system (T6SS). Because elucidating ClpV's role in the pathogenesis of T6SS is pivotal for revealing the virulence mechanism of Salmonella, in our study, clpV gene deletion mutants were constructed using a λ-red-based recombination system, and the effect of clpV mutation on SL1344's pathogenicity was examined in terms of stress resistance, motility, cytokine secretion, gut microbiota, and a BALB/c mouse model. Among the results, ClpV affected SL1344's motility and was also involved in cell invasion, adhesion, and intracellular survival in the MDBK cell model but did not affect invasion or intracellular survival in the RAW264.7 cell model. Moreover, clpV gene deletion significantly reduced the transcription levels of GBP2b, IFNB1, IL-6, NLRP3, NOS2, and TNF-α proinflammatory factor levels but significantly increased transcription levels of IL-4 and IL-10 anti-inflammatory factors. Last, ClpV appeared to closely relate to the pathogenicity of S. Typhimurium in vivo, which can change the gut environment and cause dysbiosis of gut microbiota. Our findings elucidate the functions of ClpV in S. Typhimurium and illustrating interactions between T6SS and gut microbiota help to clarify the mechanisms of the pathogenesis of foodborne diseases.

The peptidoglycan-associated lipoprotein gene mutant elicits robust immunological defense in mice against Salmonella enteritidis

Background

Salmonella enteritidis (S. enteritidis), a zoonotic pathogen with a broad host range, presents a substantial threat to global public health safety. Vaccination stands as an effective strategy for the prevention and control of S. enteritidis infection, highlighting an immediate clinical need for the creation of safe and efficient attenuated live vaccines.

Methods

In this study, a S. enteritidis peptidoglycan-associated lipoprotein (pal) gene deletion strain (Δpal), was constructed. To assess its virulence, we conducted experiments on biofilm formation capability, motility, as well as cell and mouse infection. Subsequently, we evaluated the immune-protective effect of Δpal.

Results

It was discovered that deletion of the pal gene reduced the biofilm formation capability and motility of S. enteritidis. Cell infection experiments revealed that the Δpal strain exhibited significantly decreased abilities in invasion, adhesion, and intracellular survival, with downregulation of virulence gene expression, including mgtC, invH, spvB, sipA, sipB, ssaV, csgA, and pipB. Mouse infection experiments showed that the LD50 of Δpal increased by 104 times, and its colonization ability in mouse tissue organs was significantly reduced. The results indicated that the pal gene severely affected the virulence of S. enteritidis. Further, immunogenicity evaluation of Δpal showed a significant enhancement in the lymphocyte transformation proliferation capability of immunized mice, producing high titers of specific IgG and IgA, suggesting that Δpal possesses good immunogenicity. Challenge protection tests demonstrated that the strain could provide 100% immune protection against wild-type strains in mice.

Discussion

This study proves that the pal gene influences the virulence of S. enteritidis, and Δpal could serve as a candidate strain for attenuated live vaccines, laying the foundation for the development of attenuated live vaccines against Salmonella.

Characterization of cytotoxic Citrobacter braakii isolated from human stomach

Citrobacter braakii (C. braakii) is an anaerobic, gram-negative bacterium that has been isolated from the environment, food, and humans. Infection by C. braakii has been associated with acute mucosal inflammation in the intestine, respiratory tract, and urinary tract. However, the pathogenesis of C. braakii in the gastric mucosa has not yet been clarified. In this study, the bacterium was detected in 35.5% (61/172) of patients with chronic gastritis (CG) and was closely associated with the severity of mucosal inflammation. Citrobacter braakii P1 isolated from a patient with CG exhibited urease activity and acid resistance. It contained multiple secretion systems, including a complete type I secretion system (T1SS), T5aSS and T6SS. We then predicted the potential pilus-related adhesins. Citrobacter braakii P1 diffusely adhered to AGS cells and significantly increased lactate dehydrogenase (LDH) release; the adhesion rate and LDH release were much lower in HEp-2 cells. Strain P1 also induced markedly increased mRNA and protein expression of IL-8 and TNF-α in AGS cells, and the fold increase was much higher than that in HEp-2 cells. Our results demonstrate proinflammatory and cytotoxic role of C. braakii in gastric epithelial cells, indicating the bacterium is potentially involved in inducing gastric mucosa inflammation.

In silico design and immunoinformatics analysis of a chimeric vaccine construct based on Salmonella pathogenesis factors

Currently, there are two vaccines based on killed and/or weakened Salmonella bacteria, but no recombinant vaccine is available for preventing or treating the disease. We used an in silico approach to design a multi-epitope vaccine against Salmonella using OmpA, OmpS, SopB, SseB, SthA and FilC antigens. We predicted helper T lymphocyte, cytotoxic T lymphocyte, and IFN-γ epitopes. The FilC sequence was used as a bovine TLR5 agonist, and the linkers KK, AAY, GPGPG and EAAAK were used to connect epitopes. The final sequence consisted of 747 amino acid residues, and the expressed soluble protein (∼79.6 kDa) was predicted to be both non-allergenic and antigenic. The tertiary structure of modeled protein was refined and validated, and the interactions of vaccine 3D structure were evaluated using molecular docking, and molecular dynamics simulation (RMSD, RMSF and Gyration). This structurally stable protein could interact with human TLR5. The C-ImmSim server predicted that this proposed vaccine likely induces an immune response by stimulating T and B cells, making it a potential candidate for further evaluation for the prevention and treatment of Salmonella infection.