Salmonella Enteritidis T1SS protein SiiD inhibits NLRP3 inflammasome activation via repressing the mtROS-ASC dependent pathway

Salmonella-NLRP3 Inflammasome Crosstalk: Host Defense Activation Versus Bacterial Immune Evasion Strategies

The innate immune system plays a crucial role in defending against Salmonella infection. Inflammasomes are macromolecular complexes that assemble in response to the recognition of pathogen- or danger-associated molecular patterns. These complexes serve as signaling platforms for the activation of inflammatory Caspases, which subsequently triggers the maturation and secretion of the pro-inflammatory cytokines IL-1β and IL-18. This process also initiates pyroptosis, a highly inflammatory form of programmed cell death characterized by lytic cell lysis. Salmonella are intracellular pathogens that proliferate within epithelial cells and macrophages, posing a significant public health risk in both developed and developing countries. During Salmonella infection, the canonical NLRP3 and NLRC4 inflammasome, as well as non-canonical inflammasome, are activated. Unlike NLRC4 and non-canonical inflammasomes, which play crucial roles during intestinal infection phases, the role of NLRP3 inflammasome in resisting Salmonella infection demonstrates a higher degree of complexity and uncertainty. Nonetheless, the activation of NLRP3 inflammasome, along with the downstream innate and adaptive responses, form a robust host immune barrier against potential pathogens. Therefore, successful pathogens must evolve multiple mechanisms to circumvent or counteract these immune barriers. Here we review and discuss the mechanisms of NLRP3 inflammasome activation triggered by intracellular Salmonella, as well as the multiple strategies employed by Salmonella to avoid or delay NLRP3 inflammasome activation. A deeper understanding of how NLRP3 inflammasomes recognize Salmonella and how pathogens evade NLRP3 activation has the potential to facilitate the development of novel prevention and control measures for Salmonella infection.

Activation and evasion of inflammasomes during viral and microbial infection

The inflammasome is a cytoplasmic multiprotein complex that induces the maturation of the proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18) or pyroptosis by activating caspases, which play critical roles in regulating inflammation, cell death, and various cellular processes. Multiple studies have shown that the inflammasome is a key regulator of the host defence response against pathogen infections. During the process of pathogenic microbe invasion into host cells, the host's innate immune system recognizes these microbes by activating inflammasomes, triggering inflammatory responses to clear the microbes and initiate immune responses. Moreover, microbial pathogens have evolved various mechanisms to inhibit or evade the activation of inflammasomes. Therefore, we review the interactions between viruses and microbes with inflammasomes during the invasion process, highlight the molecular mechanisms of inflammasome activation induced by microbial pathogen infection, and highlight the corresponding strategies that pathogens employ to evade inflammasome activity. Finally, we also discuss potential therapeutic strategies for the treatment of pathogenic microbial infections via the targeting of inflammasomes and their products.

The intricate interactions between inflammasomes and bacterial pathogens: Roles, mechanisms, and therapeutic potentials

Inflammasomes are intracellular multiprotein complexes that consist of a sensor, an adaptor, and a caspase enzyme to cleave interleukin (IL)-1β and IL-18 into their mature forms. In addition, caspase-1 and -11 activation results in the cleavage of gasdermin D to form pores, thereby inducing pyroptosis. Activation of the inflammasome and pyroptosis promotes host defense against pathogens, whereas dysregulation of the inflammasome can result in various pathologies. Inflammasomes exhibit versatile microbial signal detection, directly or indirectly, through cellular processes, such as ion fluctuations, reactive oxygen species generation, and the disruption of intracellular organelle function; however, bacteria have adaptive strategies to manipulate the inflammasome by altering microbe-associated molecular patterns, intercepting innate pathways with secreted effectors, and attenuating inflammatory and cell death responses. In this review, we summarize recent advances in the diverse roles of the inflammasome during bacterial infections and discuss how bacteria exploit inflammasome pathways to establish infections or persistence. In addition, we highlight the therapeutic potential of harnessing bacterial immune subversion strategies against acute and chronic bacterial infections. A more comprehensive understanding of the significance of inflammasomes in immunity and their intricate roles in the battle between bacterial pathogens and hosts will lead to the development of innovative strategies to address emerging threats posed by the expansion of drug-resistant bacterial infections.

Pyroptosis regulation by Salmonella effectors

The genus Salmonella contains the most common foodborne pathogens frequently isolated from food-producing animals and is responsible for zoonotic infections in humans and animals. Salmonella infection in humans and animals can cause intestinal damage, resulting in intestinal inflammation and disruption of intestinal homeostasis more severe cases can lead to bacteremia. Pyroptosis, a proinflammatory form of programmed cell death, is involved in many disease processes. Inflammasomes, pyroptosis, along with their respective signaling cascades, are instrumental in the preservation of intestinal homeostasis. In recent years, with the in-depth study of pyroptosis, our comprehension of the virulence factors and effector proteins in Salmonella has reached an extensive level, a deficit persists in our knowledge regarding the intrinsic pathogenic mechanisms about pyroptosis, necessitating a continued pursuit of understanding and investigation. In this review, we discuss the occurrence of pyroptosis induced by Salmonella effectors to provide new ideas for elucidating the regulatory mechanisms through which Salmonella virulence factors and effector proteins trigger pyroptosis could pave the way for novel concepts and strategies in the clinical prevention of Salmonella infections and the treatment of associated diseases.

Virulence and Antimicrobial-Resistant Gene Profiles of Salmonella spp. Isolates from Chicken Carcasses Markets in Ibague City, Colombia

Salmonella spp. is one of the leading causes of foodborne bacterial infections, with major impacts on public health and healthcare system. Salmonella is commonly transmitted via the fecal-to-oral route, and food contaminated with the bacteria (e.g., poultry products) is considered a common source of infection, being a potential risk for public health. The study aims to characterize the antimicrobial resistance- and virulence-associated genes in Salmonella isolates recovered from chicken marketed carcasses (n = 20). The presence of 14 antimicrobial and 23 virulence genes was evaluated using end-point PCR. The antimicrobial genes were detected in the following proportion among the isolates: bla TEM 100%, dfrA1 and bla CMY2 90% (n = 18), aadA1 75% (n = 15), sul1 and sul2 50% (n = 10), floR 45% (n = 9), qnrD 20% (n = 4), and aadA2 15% (n = 3). catA, sul3, qnrS, and aac(6')-Ib genes were absent in all isolates. Regarding virulence-associated genes, all Salmonella strains contain invA, fimA, avrA, msgA, sopB, and sopE. The cdtB gene was present in 95% (n = 19) of isolates, whereas spvC and spvB were present in 55% (n = 11). Other virulence genes such as spiC, lpfC, lpfA, and csgA were present in 90% (n = 18) of strains. The presence of antimicrobial and virulence genes in several Salmonella strains in chicken meat suggests the potential pathogenicity of the strains, which is relevant given the possibility of cross-contamination which represents a significant threat to public health.

NLRP3 Inflammasomes: Dual Function in Infectious Diseases

The Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome has been the most distinctive polymer protein complex. After recognizing the endogenous and exogenous danger signals, NLRP3 can cause inflammation by pyroptosis and secretion of mature, bioactive forms of IL-1β and IL-18. The NLRP3 inflammasome is essential in the genesis and progression of infectious illnesses. Herein, we provide a comprehensive review of the NLRP3 inflammasome in infectious diseases, focusing on its two-sided effects. As an essential part of host defense with a protective impact, abnormal NLRP3 inflammasome activation, however, result in a systemic high inflammatory response, leading to subsequent damage. In addition, scientific evidence of small molecules, biologics, and phytochemicals acting on the NLRP3 inflammasome has been reviewed. We believe that the NLRP3 inflammasome helps us understand the pathological mechanism of different stages of infectious diseases and that inhibitors targeting the NLRP3 inflammasome will become a new and valuable research direction for the treatment of infectious diseases.

Salmonella Enteritidis antitoxin DinJ inhibits NLRP3-dependent canonical inflammasome activation in macrophages

The inflammasome is a pivotal component of the innate immune system, acting as a multiprotein complex that plays an essential role in detecting and responding to microbial infections. Salmonella Enteritidis have evolved multiple mechanisms to regulate inflammasome activation and evade host immune system clearance. Through screening S. Enteritidis C50336ΔfliC transposon mutant library, we found that the insertion mutant of dinJ increased inflammasome activation. In this study, we demonstrated the genetic connection between the antitoxin DinJ and the toxin YafQ in S. Enteritidis, confirming their co-transcription. The deletion mutant ΔfliCΔdinJ increased cell death and IL-1β secretion in J774A.1 cells. Western blotting analysis further showed elevated cleaved Caspase-1 product (p10 subunits) and IL-1β secretion in cells infected with ΔfliCΔdinJ compared to cells infected with ΔfliC. DinJ was found to inhibit canonical inflammasome activation using primary bone marrow-derived macrophages (BMDMs) from Casp-/- C57BL/6 mice. Furthermore, DinJ specifically inhibited NLRP3 inflammasome activation, as demonstrated in BMDMs from Nlrp3-/- and Nlrc4-/- mice. Fluorescence resonance energy transfer (FRET) experiments confirmed the translocation of DinJ into host cells during infection. Finally, we revealed that DinJ could inhibit the secretion of IL-1β and IL-18 in vivo, contributing to S. Enteritidis evading host immune clearance. In summary, our findings provide insights into the role of DinJ in modulating the inflammasome response during S. Enteritidis infection, highlighting its impact on inhibiting inflammasome activation and immune evasion.

The NLRP3 molecule is responsible for mediating the pyroptosis of intestinal mucosa cells and plays a crucial role in salmonellosis enteritis in chicks

Salmonella enteritis in poultry can result in reduced immune function, decreased growth rate, and increased mortality. Many farm salmonella strains have developed severe drug resistance and are less susceptible to multiple antibiotics. In the post-antibiotic era, it is of great significance to identify the mechanism of salmonella-induced enteritis in chicks to protect their health and ensure food safety. This article will elucidate the activation mechanism of NOD-like receptor protein 3 (NLRP3) inflammasomes in Salmonella enteritis and review the research on interventions targeting NLRP3 inflammasomes.

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.

The NLRP3 inflammasome in viral infection (Review)

The interplay between pathogen and host determines the immune response during viral infection. The Nod‑like receptor (NLR) protein 3 inflammasome is a multiprotein complex that induces the activation of inflammatory caspases and the release of IL‑1β, which play an important role in the innate immune responses. In the present review, the mechanisms of the NLR family pyrin domain containing 3 inflammasome activation and its dysregulation in viral infection were addressed.