Salmonella Interacts With Autophagy to Offense or Defense

Excessive autophagy-inducing and highly penetrable biomineralized bacteria for multimodal imaging-guided and mild hyperthermia-enhanced immunogenic cell death

The tumor microenvironment, characterized by hypoxia, supports the efficacy of anaerobic bacteria like attenuated S. typhimurium in cancer therapies. These bacteria target and penetrate deep tumor regions, significantly reducing tumor size but often lead to tumor regrowth due to limited long-term efficacy. To enhance the therapeutic impact, a novel biohybrid system, S@UIL, has been developed by coating S. typhimurium with a zirconium-based nanoscale metal-organic framework (UiO-66-NH2) loaded with indocyanine green (ICG) and luteolin (LUT). This system maintains the bacteria's tumor-targeting ability while increasing the penetration and therapeutic effectiveness through excessive autophagy and mild hyperthermia. In a subcutaneous colon cancer model, the integration of LUT and ICG promotes autophagic cell death and photothermal sensitization, leading to the release of damage-associated molecular patterns (DAMPs). These DAMPs activate immune responses through dendritic cells and T-cells, enhancing immunogenic cell death (ICD) and potentially reducing immune evasion by tumors. This single-administration approach also integrates multimodal imaging capabilities, providing a promising strategy for improved tumor ICD induction and cancer progression inhibition.

Programmed cell death and Salmonella pathogenesis: an interactive overview

Programmed cell death (PCD) is the collective term for the intrinsically regulated death of cells. Various types of cell death are triggered by their own programmed regulation during the growth and development of organisms, as well as in response to environmental and disease stresses. PCD encompasses apoptosis, pyroptosis, necroptosis, autophagy, and other forms. PCD plays a crucial role not only in the growth and development of organisms but also in serving as a component of the host innate immune defense and as a bacterial virulence strategy employed by pathogens during invasion. The zoonotic pathogen Salmonella has the ability to modulate multiple forms of PCD, including apoptosis, pyroptosis, necroptosis, and autophagy, within the host organism. This modulation subsequently impacts the bacterial infection process. This review aims to consolidate recent findings regarding the mechanisms by which Salmonella initiates and controls cell death signaling, the ways in which various forms of cell death can impede or restrict bacterial proliferation, and the interplay between cell death and innate immune pathways that can counteract Salmonella-induced suppression of host cell death. Ultimately, these insights may contribute novel perspectives for the diagnosis and treatment of clinical Salmonella-related diseases.

Hydrogen Sulfide and Liver Health: Insights into Liver Diseases

Significance: Hydrogen sulfide (H2S) is a recently recognized gasotransmitter involved in physiological and pathological conditions in mammals. It protects organs from oxidative stress, inflammation, hypertension, and cell death. With abundant expression of H2S-production enzymes, the liver is closely linked to H2S signaling. Recent Advances: Hepatic H2S comes from various sources, including gut microbiota, exogenous sulfur salts, and endogenous production. Recent studies highlight the importance of hepatic H2S in liver diseases such as nonalcoholic fatty liver disease (NAFLD), liver injury, and cancer, particularly at advanced stages. Endogenous H2S production deficiency is associated with severe liver disease, while exogenous H2S donors protect against liver dysfunction. Critical Issues: However, the roles of H2S in NAFLD, liver injury, and liver cancer are still debated, and its effects depend on donor type, dosage, treatment duration, and cell type, suggesting a multifaceted role. This review aimed to critically evaluate H2S production, metabolism, mode of action, and roles in liver function and disease. Future Direction: Understanding H2S's precise roles and mechanisms in liver health will advance potential therapeutic applications in preclinical and clinical research. Targeting H2S-producing enzymes and exogenous H2S sources, alone or in combination with other drugs, could be explored. Quantifying endogenous H2S levels may aid in diagnosing and managing liver diseases. Antioxid. Redox Signal. 40, 122-144.

RhoB promotes Salmonella survival by regulating autophagy

Salmonella enterica serovar Typhimurium manipulates cellular Rho GTPases for host cell invasion by effector protein translocation via the Type III Secretion System (T3SS). The two Guanine nucleotide exchange (GEF) mimicking factors SopE and -E2 and the inositol phosphate phosphatase (PiPase) SopB activate the Rho GTPases Rac1, Cdc42 and RhoA, thereby mediating bacterial invasion. S. Typhimurium lacking these three effector proteins are largely invasion-defective. Type III secretion is crucial for both early and later phases of the intracellular life of S. Typhimurium. Here we investigated whether and how the small GTPase RhoB, known to localize on endomembrane vesicles and at the invasion site of S. Typhimurium, contributes to bacterial invasion and to subsequent steps relevant for S. Typhimurium lifestyle. We show that RhoB is significantly upregulated within hours of Salmonella infection. This effect depends on the presence of the bacterial effector SopB, but does not require its phosphatase activity. Our data reveal that SopB and RhoB bind to each other, and that RhoB localizes on early phagosomes of intracellular S. Typhimurium. Whereas both SopB and RhoB promote intracellular survival of Salmonella, RhoB is specifically required for Salmonella-induced upregulation of autophagy. Finally, in the absence of RhoB, vacuolar escape and cytosolic hyper-replication of S. Typhimurium is diminished. Our findings thus uncover a role for RhoB in Salmonella-induced autophagy, which supports intracellular survival of the bacterium and is promoted through a positive feedback loop by the Salmonella effector SopB.

Lactiplantibacillus plantarum Postbiotics Suppress Salmonella Infection via Modulating Bacterial Pathogenicity, Autophagy and Inflammasome in Mice

Our study aimed to explore the effects of postbiotics on protecting against Salmonella infection in mice and clarify the underlying mechanisms. Eighty 5-week-old C57BL/6 mice were gavaged daily with Lactiplantibacillus plantarum (LP)-derived postbiotics (heat-killed bacteria, LPBinactive; culture supernatant, LPC) or the active bacteria (LPBactive), and gavaged with Salmonella enterica Typhimurium (ST). The Turbidimetry test and agar diffusion assay indicated that LPC directly inhibited Salmonella growth. Real-time PCR and biofilm inhibition assay showed that LPC had a strong ability in suppressing Salmonella pathogenicity by reducing virulence genes (SopE, SopB, InvA, InvF, SipB, HilA, SipA and SopD2), pili genes (FilF, SefA, LpfA, FimF), flagellum genes (FlhD, FliC, FliD) and biofilm formation. LP postbiotics were more effective than LP on attenuating ST-induced intestinal damage in mice, as indicated by increasing villus/crypt ratio and increasing the expression levels of tight junction proteins (Occludin and Claudin-1). Elisa assay showed that LP postbiotics significantly reduced ST-induced inflammation by regulating the levels of inflammatory cytokines (the increased IL-4 and IL-10 and the decreased TNF-α) in serum and ileum (p < 0.05). Furthermore, LP postbiotics inhibited the activation of NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome by decreasing the protein expression of NLRP3 and Caspase-1, and the gene expression of Caspase-1, IL-1β and IL-18. Meanwhile, both LPC and LPB observably activated autophagy under ST infection, as indicated by the up-regulated expression of LC3 and Beclin1 and the downregulated p62 level (p < 0.05). Finally, we found that LP postbiotics could trigger an AMP-activated protein kinase (AMPK) signaling pathway to induce autophagy. In summary, Lactiplantibacillus plantarum-derived postbiotics alleviated Salmonella infection via modulating bacterial pathogenicity, autophagy and NLRP3 inflammasome in mice. Our results confirmed the effectiveness of postbiotics agents in the control of Salmonella infection.

HSPA8 regulates anti-bacterial autophagy through liquid-liquid phase separation

HSPA8 (heat shock protein family A (Hsp70) member 8) plays a significant role in the autophagic degradation of proteins, however, its effect on protein stabilization and anti-bacterial autophagy remains unknown. Here, it is discovered that HSPA8, as a binding partner of RHOB and BECN1, induce autophagy for intracellular bacteria clearance. Using its NBD and LID domains, HSPA8 physically binds to RHOB residues 1-42 and 89-118 as well as to BECN1 ECD domain, preventing RHOB and BECN1 degradation. Intriguingly, HSPA8 contains predicted intrinsically disordered regions (IDRs), and drives liquid-liquid phase separation (LLPS) to concentrate RHOB and BECN1 into HSPA8-formed liquid-phase droplets, resulting in improved RHOB and BECN1 interactions. Our study reveals a novel role and mechanism of HSPA8 in modulating anti-bacterial autophagy, and highlights the effect of LLPS-related HSPA8-RHOB-BECN1 complex on enhancing protein interaction and stabilization, which improves the understanding of autophagy-mediated defense against bacteria.

A novel role for Helicobacter pylori cytotoxin-associated gene A in negative regulation of autophagy in human gastric cells

BACKGROUND

Autophagy plays an important role in carcinogenesis and tumor progression in many cancers, including gastric cancer. Cytotoxin-associated gene A (CagA) is a well-known virulent factor in Helicobacter pylori (H. pylori) infection that plays a critical role in gastric inflammation and gastric cancer development. However, its role in autophagy during these processes remains unclear. Therefore, we aimed to clarify the role of CagA in autophagy in CagA-related inflammation.

METHODS

We evaluated the autophagic index of AGS cells infected with wild-type cagA-positive H. pylori (Hp-WT) and cagA-knockout H. pylori (Hp-ΔcagA) and rat gastric mucosal (RGM1) cells transfected with CagA genes. To identify the mechanisms underlying the down regulation of autophagy in AGS cells infected with H. pylori, we evaluated protein and mRNA expression levels of autophagy core proteins using western blotting and quantitative reverse transcription-polymerase chain reaction (RT-PCR). To determine whether autophagy induced the expression of the pro-inflammatory mediator, cyclooxygenase-2 (COX-2), we evaluated COX-2 expression in AGS cells treated with an autophagy inducer and inhibitor and infected with H. pylori. In addition, we evaluated whether COX-2 protein expression in AGS cells influenced beclin-1 (BECN1) expression with si-RNA transfection when infected with H. pylori.

RESULTS

Autophagic flux assay using chloroquine showed that autophagy in AGS cells was significantly suppressed after H. pylori infection. The autophagic index of AGS cells infected with Hp-WT was decreased significantly when compared with that in AGS cells infected with Hp-ΔcagA. The autophagic index of RGM1 cells transfected with CagA was lower, suggesting that CagA inhibits autophagy. In addition, BECN1 expression levels in AGS cells infected with Hp-WT were reduced compared to those in AGS cells infected with Hp-ΔcagA. Furthermore, COX-2 expression in AGS cells infected with H. pylori was controlled in an autophagy-dependent manner. When AGS cells were transfected with small interfering RNA specific for BECN1 and infected with Hp-WT and Hp-ΔcagA, COX-2 was upregulated significantly in cells infected with Hp-ΔcagA.

CONCLUSIONS

In conclusion, the H. pylori CagA protein negatively regulated autophagy by downregulating BECN1. CagA-induced autophagy inhibition may be a causative factor in promoting pro-inflammatory mediator production in human gastric epithelial cells.

p38MAPK/MK2 signaling stimulates host cells autophagy pathways to restrict Salmonella infection

Autophagy plays an important role in recognizing and protecting cells from invading intracellular pathogens such as Salmonella. In this work, we investigated the role of p38MAPK/MK2 in modulating the host cell susceptibility to Salmonella infection. Inhibition of p38MAPK or MK2 led to a significant increase of bacterial counts in Salmonella infected mouse embryonic fibroblasts (MEFs), as well as in MK2-deficient (Mk2-/-) cells. Furthermore, western blot analysis showed that Mk2-/- cells have lower level of LC3 lipidation, which is the indicator of general autophagy compared to Mk2-rescued cells. In Mk2-/- cells, we also observed lower activated TANK-binding kinase-1 phosphorylation on Ser172 and p62/SQTM1-Ser403 phosphorylation, which are important to promote the translocation of p62 to ubiquitinated microbes and required for efficient autophagy of bacteria. Furthermore, immunofluorescence analysis revealed reduced colocalization of Salmonella with LC3 and p62 in MEFs. Inhibition of autophagy with bafilomycin A1 showed increased bacterial counts in treated cells compared to control cell. Overall, these results indicate that p38MAPK/MK2-mediated protein phosphorylation modulates the host cell susceptibility to Salmonella infection by affecting the autophagy pathways.

Impact and Advances in the Role of Bacterial Extracellular Vesicles in Neurodegenerative Disease and Its Therapeutics

Bacterial Extracellular Vesicles (BEVs) possess the capability of intracellular interactions with other cells, and, hence, can be utilized as an efficient cargo for worldwide delivery of therapeutic substances such as monoclonal antibodies, proteins, plasmids, siRNA, and small molecules for the treatment of neurodegenerative diseases (NDs). BEVs additionally possess a remarkable capacity for delivering these therapeutics across the blood-brain barrier to treat Alzheimer's disease (AD). This review summarizes the role and advancement of BEVs for NDs, AD, and their treatment. Additionally, it investigates the critical BEV networks in the microbiome-gut-brain axis, their defensive and offensive roles in NDs, and their interaction with NDs. Furthermore, the part of BEVs in the neuroimmune system and their interference with ND, as well as the risk factors made by BEVs in the autophagy-lysosomal pathway and their potential outcomes on ND, are all discussed. To conclude, this review aims to gain a better understanding of the credentials of BEVs in NDs and possibly discover new therapeutic strategies.

Macrophages in immunoregulation and therapeutics

Macrophages exist in various tissues, several body cavities, and around mucosal surfaces and are a vital part of the innate immune system for host defense against many pathogens and cancers. Macrophages possess binary M1/M2 macrophage polarization settings, which perform a central role in an array of immune tasks via intrinsic signal cascades and, therefore, must be precisely regulated. Many crucial questions about macrophage signaling and immune modulation are yet to be uncovered. In addition, the clinical importance of tumor-associated macrophages is becoming more widely recognized as significant progress has been made in understanding their biology. Moreover, they are an integral part of the tumor microenvironment, playing a part in the regulation of a wide variety of processes including angiogenesis, extracellular matrix transformation, cancer cell proliferation, metastasis, immunosuppression, and resistance to chemotherapeutic and checkpoint blockade immunotherapies. Herein, we discuss immune regulation in macrophage polarization and signaling, mechanical stresses and modulation, metabolic signaling pathways, mitochondrial and transcriptional, and epigenetic regulation. Furthermore, we have broadly extended the understanding of macrophages in extracellular traps and the essential roles of autophagy and aging in regulating macrophage functions. Moreover, we discussed recent advances in macrophages-mediated immune regulation of autoimmune diseases and tumorigenesis. Lastly, we discussed targeted macrophage therapy to portray prospective targets for therapeutic strategies in health and diseases.

Salmonella Enteritidis RfbD enhances bacterial colonization and virulence through inhibiting autophagy

Autophagy is a crucial innate immune response that clears pathogens intracellularly. Salmonella enterica serovar Enteritidis (S.E) has emerged as one of the most important food-borne pathogens. Here, we reported that dTDP-4-dehydro-β-ւ-rhamnose reductase (RfbD) was able to enhance bacterial colonization in vivo and in vitro by regulating autophagy. We screened the transposon mutant library of Salmonella Enteritidis strain Z11 by High-Content Analysis System, found that rfbD gene has an effect on autophagy. The Z11ΔrfbD-infected group showed greater expression of LC3-II than the Z11-infected group in HeLa, RAW264.7, and J774A.1 cells. Overall, the survival of Z11ΔrfbD in RAW264.7 cells was reduced after 8 h of infection compared to that of the Z11 wild-type strain. In addition, we observed that inhibition of autophagic flux significantly increased the survival of Z11ΔrfbD in RAW264.7 cells. Mice infection experiments revealed that Z11ΔrfbD virulence was significantly reduced, and bacterial load was reduced in the liver and cecum in mice model, and LC3-II expression was significantly increased. These findings indicate an important role of Salmonella Enteritidis protein as a strategy to suppress autophagy and provides new ideas for manipulating autophagy as a novel strategy to treat infectious diseases.

Japanese Flounder pol-miR-155 Is Involved in Edwardsiella tarda Infection via ATG3

MicroRNAs (miRNAs) are small RNA molecules that function in the post-transcriptionally regulation of the expression of diverse genes, including those involved in immune defense. Edwardsiella tarda can infect a broad range of hosts and cause severe disease in aquatic species, including Japanese flounder (Paralichthys olivaceus). In this study, we examined the regulation mechanism of a flounder miRNA, pol-miR-155, during the infection of E. tarda. Pol-miR-155 was identified to target flounder ATG3. Overexpression of pol-miR-155 or knockdown of ATG3 expression suppressed autophagy and promoted the intracellular replication of E. tarda in flounder cells. Overexpression of pol-miR-155 activated the NF-κB signaling pathway and further promoted the expression of downstream immune related genes of interleukin (IL)-6 and IL-8. These results unraveled the regulatory effect of pol-miR-155 in autophagy and in E. tarda infection.

Manipulation of host immune defenses by effector proteins delivered from multiple secretion systems of Salmonella and its application in vaccine research

Salmonella is an important zoonotic bacterial species and hazardous for the health of human beings and livestock globally. Depending on the host, Salmonella can cause diseases ranging from gastroenteritis to life-threatening systemic infection. In this review, we discuss the effector proteins used by Salmonella to evade or manipulate four different levels of host immune defenses: commensal flora, intestinal epithelial-mucosal barrier, innate and adaptive immunity. At present, Salmonella has evolved a variety of strategies against host defense mechanisms, among which various effector proteins delivered by the secretory systems play a key role. During its passage through the digestive system, Salmonella has to face the intact intestinal epithelial barrier as well as competition with commensal flora. After invasion of host cells, Salmonella manipulates inflammatory pathways, ubiquitination and autophagy processes with the help of effector proteins. Finally, Salmonella evades the adaptive immune system by interfering the migration of dendritic cells and interacting with T and B lymphocytes. In conclusion, Salmonella can manipulate multiple aspects of host defense to promote its replication in the host.

Cytosolic galectin-4 enchains bacteria, restricts their motility, and promotes inflammasome activation in intestinal epithelial cells

Galectin-4, a member of the galectin family of animal glycan-binding proteins (GBPs), is specifically expressed in gastrointestinal epithelial cells and is known to be able to bind microbes. However, its function in host-gut microbe interactions remains unknown. Here, we show that intracellular galectin-4 in intestinal epithelial cells (IECs) coats cytosolic Salmonella enterica serovar Worthington and induces the formation of bacterial chains and aggregates. Galectin-4 enchains bacteria during their growth by binding to the O-antigen of lipopolysaccharides. Furthermore, the binding of galectin-4 to bacterial surfaces restricts intracellular bacterial motility. Galectin-4 enhances caspase-1 activation and mature IL-18 production in infected IECs especially when autophagy is inhibited. Finally, orally administered S. enterica serovar Worthington, which is recognized by human galectin-4 but not mouse galectin-4, translocated from the intestines to mesenteric lymph nodes less effectively in human galectin-4-transgenic mice than in littermate controls. Our results suggest that galectin-4 plays an important role in host-gut microbe interactions and prevents the dissemination of pathogens. The results of the study revealed a novel mechanism of host-microbe interactions that involves the direct binding of cytosolic lectins to glycans on intracellular microbes.

Salmonella effector SopF regulates PANoptosis of intestinal epithelial cells to aggravate systemic infection

SopF, a newly discovered effector secreted by Salmonella pathogenicity island-1 type III secretion system (T3SS1), was reported to target phosphoinositide on host cell membrane and aggravate systemic infection, while its functional relevance and underlying mechanisms have yet to be elucidated. PANoptosis (pyroptosis, apoptosis, and necroptosis) of intestinal epithelial cells (IECs) has been characterized as a pivotal host defense to limit the dissemination of foodborne pathogens, whereas the effect of SopF on IECs PANoptosis induced by Salmonella is rather limited. Here, we show that SopF can attenuate intestinal inflammation and suppress IECs expulsion to promote bacterial dissemination in mice infected with Salmonella enterica serovar Typhimurium (S. Typhimurium). We revealed that SopF could activate phosphoinositide-dependent protein kinase-1 (PDK1) to phosphorylate p90 ribosomal S6 kinase (RSK) which down-regulated Caspase-8 activation. Caspase-8 inactivated by SopF resulted in inhibition of pyroptosis and apoptosis, but promotion of necroptosis. The administration of both AR-12 (PDK1 inhibitor) and BI-D1870 (RSK inhibitor) potentially overcame Caspase-8 blockade and subverted PANoptosis challenged by SopF. Collectively, these findings demonstrate that this virulence strategy elicited by SopF aggregates systemic infection via modulating IEC PANoptosis through PDK1-RSK signaling, which throws light on novel functions of bacterial effectors, as well as a mechanism employed by pathogens to counteract host immune defense.

Chemical modulation of SQSTM1/p62-mediated xenophagy that targets a broad range of pathogenic bacteria

The N-degron pathway is a proteolytic system in which the N-terminal degrons (N-degrons) of proteins, such as arginine (Nt-Arg), induce the degradation of proteins and subcellular organelles via the ubiquitin-proteasome system (UPS) or macroautophagy/autophagy-lysosome system (hereafter autophagy). Here, we developed the chemical mimics of the N-degron Nt-Arg as a pharmaceutical means to induce targeted degradation of intracellular bacteria via autophagy, such as Salmonella enterica serovar Typhimurium (S. Typhimurium), Escherichia coli, and Streptococcus pyogenes as well as Mycobacterium tuberculosis (Mtb). Upon binding the ZZ domain of the autophagic cargo receptor SQSTM1/p62 (sequestosome 1), these chemicals induced the biogenesis and recruitment of autophagic membranes to intracellular bacteria via SQSTM1, leading to lysosomal degradation. The antimicrobial efficacy was independent of rapamycin-modulated core autophagic pathways and synergistic with the reduced production of inflammatory cytokines. In mice, these drugs exhibited antimicrobial efficacy for S. Typhimurium, Bacillus Calmette-Guérin (BCG), and Mtb as well as multidrug-resistant Mtb and inhibited the production of inflammatory cytokines. This dual mode of action in xenophagy and inflammation significantly protected mice from inflammatory lesions in the lungs and other tissues caused by all the tested bacterial strains. Our results suggest that the N-degron pathway provides a therapeutic target in host-directed therapeutics for a broad range of drug-resistant intracellular pathogens.Abbreviations: ATG: autophagy-related gene; BCG: Bacillus Calmette-Guérin; BMDMs: bone marrow-derived macrophages; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CFUs: colony-forming units; CXCL: C-X-C motif chemokine ligand; EGFP: enhanced green fluorescent protein; IL1B/IL-1β: interleukin 1 beta; IL6: interleukin 6; LIR: MAP1LC3/LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; Mtb: Mycobacterium tuberculosis; MTOR: mechanistic target of rapamycin kinase; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PB1: Phox and Bem1; SQSTM1/p62: sequestosome 1; S. Typhimurium: Salmonella enterica serovar Typhimurium; TAX1BP1: Tax1 binding protein 1; TNF: tumor necrosis factor; UBA: ubiquitin-associated.

Downregulation of AKT/mTOR signaling pathway for Salmonella-mediated autophagy in human anaplastic thyroid cancer

Thyroid cancer has been known as the most common endocrine malignancy. Although majority of thyroid cancer types respond well to conventional treatment including surgery and radioactive iodine therapy, about 10% of those with differentiated thyroid cancer will present distant metastasis and will have persistent or recurrent disease. Even more serious is a rare type of thyroid cancer called anaplastic thyroid cancer (ATC), which accounts for about 1%, has been demonstrated as the most lethal and aggressive form of human malignancy. Unfortunately, these tumors are also frequently resistant to traditional therapy. Previous study have shown that Salmonella inhibits tumor growth, in part, by inducing autophagy - a cellular process that is important in the innate and adaptive immunity in response to viral or bacterial infection. In our study, we intended to investigate whether Salmonella can inhibit tumor growth by inducing autophagy, specifically in thyroid cancer and elucidate the possible molecular mechanism. In order to determine the signaling pathway involved in tumor cell autophagy, we used Salmonella to treat ATC cells line ASH-3 and KMH-2 in vitro. The autophagic markers, particularly autophagy-related gene 6 (Beclin-1), microtubule-associated protein 1A/1B-light chain 3 (LC3) and p62, were observed to be differentially expressed after infection with Salmonella indicating an activated autophagy in ATC cells. In addition, the protein expression levels of phospho-protein kinase B (P-AKT), phospho-mammalian targets of rapamycin (P-mTOR), phospho-p70 ribosomal s6 kinase (P-p70S6K) in tumor cells were decreased after Salmonella infection. In vivo, we also found that substantial cell numbers of Salmonella targeted tumor tissue, and regulated anti-tumor mechanisms. Our findings showed that Salmonella activated autophagic signaling pathway and inhibited ATC tumor growth via downregulation of AKT/mTOR pathway.

The NEL Family of Bacterial E3 Ubiquitin Ligases

Some pathogenic or symbiotic Gram-negative bacteria can manipulate the ubiquitination system of the eukaryotic host cell using a variety of strategies. Members of the genera Salmonella, Shigella, Sinorhizobium, and Ralstonia, among others, express E3 ubiquitin ligases that belong to the NEL family. These bacteria use type III secretion systems to translocate these proteins into host cells, where they will find their targets. In this review, we first introduce type III secretion systems and the ubiquitination process and consider the various ways bacteria use to alter the ubiquitin ligation machinery. We then focus on the members of the NEL family, their expression, translocation, and subcellular localization in the host cell, and we review what is known about the structure of these proteins, their function in virulence or symbiosis, and their specific targets.

Cross-Talk Between the Intestinal Epithelium and Salmonella Typhimurium

Salmonella enterica serovars are invasive gram-negative bacteria, causing a wide range of diseases from gastroenteritis to typhoid fever, representing a public health threat around the world. Salmonella gains access to the intestinal lumen after oral ingestion of contaminated food or water. The crucial initial step to establish infection is the interaction with the intestinal epithelium. Human-adapted serovars such as S. Typhi or S. Paratyphi disseminate to systemic organs and induce life-threatening disease known as typhoid fever, whereas broad-host serovars such as S. Typhimurium usually are limited to the intestine and responsible for gastroenteritis in humans. To overcome intestinal epithelial barrier, Salmonella developed mechanisms to induce cellular invasion, intracellular replication and to face host defence mechanisms. Depending on the serovar and the respective host organism, disease symptoms differ and are linked to the ability of the bacteria to manipulate the epithelial barrier for its own profit and cross the intestinal epithelium.

This review will focus on S. Typhimurium (STm). To better understand STm pathogenesis, it is crucial to characterize the crosstalk between STm and the intestinal epithelium and decipher the mechanisms and epithelial cell types involved. Thus, the purpose of this review is to summarize our current knowledge on the molecular dialogue between STm and the various cell types constituting the intestinal epithelium with a focus on the mechanisms developed by STm to cross the intestinal epithelium and access to subepithelial or systemic sites and survive host defense mechanisms.

Salmonella enterica serovar Typhi influences inflammation and autophagy in macrophages

Salmonella enterica serovar Typhi (S. Typhi) is a human enteropathogen that can survive in macrophages and cause systemic infection. Autophagy and inflammation are two important immune responses of macrophages that contribute to the elimination of pathogens. However, Salmonella has derived many strategies to evade inflammation and autophagy. This study investigated inflammation-related NF-κB signaling pathways and autophagy in S. Typhi-infected macrophages. RNA-seq and quantitative real-time PCR indicated that mRNA levels of NF-κB signaling pathway and autophagy-related genes were dynamically influenced in S. Typhi-infected macrophages. Western blots revealed that S. Typhi activated the NF-κB signaling pathway and induced the expression of inhibitor protein IκBζ. In addition, S. Typhi enhanced autophagy during early stages of infection and may inhibit autophagy during late stages of infection. Thus, we propose that S. Typhi can influence the NF-κB signaling pathway and autophagy in macrophages.

Activation of Autophagy Through the NLRP3/mTOR Pathway: A Potential Mechanism for Alleviation of Pneumonia by QingFei Yin

QingFei Yin (QFY), a Chinese traditional medicine recipe, is known for its excellent therapeutic pharmacological effects for the treatment of bacterial lung infections, although its molecular mechanism of action remains unknown. Here, QFY chemical composition was determined using a High-Performance Liquid Chromatography-Mass (HPLC-MS/MS)-based method then QFY was evaluated for protective pharmacological effects against pneumonia using two models: a Streptococcus pneumoniae-induced in vivo mouse model and an in vitro pneumolysin (PLY)-induced murine lung alveolar-derived MH-S cell line-based model. Notably, QFY exerted prominent anti-pneumonia effects both in vivo and in vitro. To further explore QFY protective effects, 4D label-free proteomics analysis, pathologic evaluation, and immunohistochemical (IHC) analysis were conducted to identify cellular pathways involved in QFY protection. Notably, our results indicated that NF-κB/NLRP3 and autophagy pathways may contribute to pharmacological effects associated with QFY-based protection. Briefly, QFY triggered autophagy via down-regulation of upstream NLRP3/mTOR signaling pathway events, resulting in the amelioration of inflammatory injury. Collectively, our results revealed molecular mechanisms underlying QFY protection against pneumonia as a foundation for the future development of novel treatments to combat this disease and reduce antibiotic abuse.

Perturbation of ATG16L1 function impairs the biogenesis of Salmonella and Coxiella replication vacuoles

Anti-bacterial autophagy, known as xenophagy, is a host innate immune response that targets invading pathogens for degradation. Some intracellular bacteria, such as the enteric pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium), utilize effector proteins to interfere with autophagy. One such S. Typhimurium effector, SopF, inhibits recruitment of ATG16L1 to damaged Salmonella-containing vacuoles (SCVs), thereby inhibiting the host xenophagic response. SopF is also required to maintain the integrity of the SCV during the early stages of infection. Here we show disruption of the SopF-ATG16L1 interaction leads to an increased proportion of cytosolic S. Typhimurium. Furthermore, SopF was utilized as a molecular tool to examine the requirement for ATG16L1 in the intracellular lifestyle of Coxiella burnetii, a bacterium that requires a functional autophagy pathway to replicate efficiently and form a single, spacious vacuole called the Coxiella-containing vacuole (CCV). ATG16L1 is required for CCV expansion and fusion but does not influence C. burnetii replication. In contrast, SopF did not affect CCV formation or replication, demonstrating that the contribution of ATG16L1 to CCV biogenesis is via its role in autophagy, not xenophagy. This study highlights the diverse capabilities of bacterial effector proteins to dissect the molecular details of host-pathogen interactions.

Peptidoglycan editing in non-proliferating intracellular Salmonella as source of interference with immune signaling

Salmonella enterica causes intracellular infections that can be limited to the intestine or spread to deeper tissues. In most cases, intracellular bacteria show moderate growth. How these bacteria face host defenses that recognize peptidoglycan, is poorly understood. Here, we report a high-resolution structural analysis of the minute amounts of peptidoglycan purified from S. enterica serovar Typhimurium (S. Typhimurium) infecting fibroblasts, a cell type in which this pathogen undergoes moderate growth and persists for days intracellularly. The peptidoglycan of these non-proliferating bacteria contains atypical crosslinked muropeptides with stem peptides trimmed at the L-alanine-D-glutamic acid-(γ) or D-glutamic acid-(γ)-meso-diaminopimelic acid motifs, both sensed by intracellular immune receptors. This peptidoglycan has a reduced glycan chain average length and ~30% increase in the L,D-crosslink, a type of bridge shared by all the atypical crosslinked muropeptides identified. The L,D-transpeptidases LdtD (YcbB) and LdtE (YnhG) are responsible for the formation of these L,D-bridges in the peptidoglycan of intracellular bacteria. We also identified in a fraction of muropeptides an unprecedented modification in the peptidoglycan of intracellular S. Typhimurium consisting of the amino alcohol alaninol replacing the terminal (fourth) D-alanine. Alaninol was still detectable in the peptidoglycan of a double mutant lacking LdtD and LdtE, thereby ruling out the contribution of these enzymes to this chemical modification. Remarkably, all multiple mutants tested lacking candidate enzymes that either trim stem peptides or form the L,D-bridges retain the capacity to modify the terminal D-alanine to alaninol and all attenuate NF-κB nuclear translocation. These data inferred a potential role of alaninol-containing muropeptides in attenuating pro-inflammatory signaling, which was confirmed with a synthetic tetrapeptide bearing such amino alcohol. We suggest that the modification of D-alanine to alaninol in the peptidoglycan of non-proliferating intracellular S. Typhimurium is an editing process exploited by this pathogen to evade immune recognition inside host cells.

The peptidoglycan, built as a giant polymer of glycan chains crosslinked with short peptides, is essential for cell shape and survival in most bacteria. Its unique chemistry is recognized by innate immune receptors, thereby enabling neutralization of invading microbes. A striking feature of the peptidoglycan is its constant remodeling by a plethora of endogenous enzymes. In addition, some bacterial pathogens introduce structural modifications that interfere with immune recognition. These modifications have been characterized in pathogens mostly in laboratory nutrient media. Whether facultative intracellular pathogens modify peptidoglycan structure inside host cells, was unknown. The work presented here shows that non-proliferating Salmonella enterica serovar Typhimurium remodels the peptidoglycan structure in response to intracellular cues and that some of these modifications involve unprecedented changes as the presence of an amino alcohol that hampers activation of the master immune regulator NF-κB. Peptidoglycan editing might therefore empower persistence of bacterial pathogens in the intracellular niche.

Effects of Dietary Supplementation With Bacillus subtilis, as an Alternative to Antibiotics, on Growth Performance, Serum Immunity, and Intestinal Health in Broiler Chickens

Bacillus subtilis (B. subtilis) as in-feed probiotics is a potential alternative for antibiotic growth promoters (AGP) in the poultry industry. The current study investigated the effects of B. subtilis on the performance, immunity, gut microbiota, and intestinal barrier function of broiler chickens. A 42-day feeding trial was conducted with a total of 600 1-day-old Arbor Acres broilers with similar initial body weight, which was randomly divided into one of five dietary treatments: the basal diet (Ctrl), Ctrl + virginiamycin (AGP), Ctrl + B. subtilis A (BSA), Ctrl + B. subtilis B (BSB), and Ctrl + B. subtilis A + B (1:1, BSAB). The results showed significantly increased average daily gain in a step-wise manner from the control, B. subtilis, and to the AGP groups. The mortality rate of the B. subtilis group was significantly lower than the AGP group. The concentrations of serum immunoglobulin (Ig) G (IgG), IgA, and IgM in the B. subtilis and AGP groups were higher than the control group, and the B. subtilis groups had the highest content of serum lysozyme and relative weight of thymus. Dietary B. subtilis increased the relative length of ileum and the relative weight of jejunum compared with the AGP group. The villus height (V), crypt depth (C), V/C, and intestinal wall thickness of the jejunum in the B. subtilis and AGP groups were increased relative to the control group. Dietary B. subtilis increased the messenger RNA (mRNA) expression of ZO-1, Occludin, and Claudin-1, the same as AGP. The contents of lactic acid, succinic acid, and butyric acid in the ileum and cecum were increased by dietary B. subtilis. Dietary B. subtilis significantly increased the lactobacillus and bifidobacteria in the ileum and cecum and decreased the coliforms and Clostridium perfringens in the cecum. The improved performance and decreased mortality rate observed in the feeding trial could be accrued to the positive effects of B. subtilis on the immune response capacity, gut health, and gut microflora balance, and the combination of two strains showed additional benefits on the intestinal morphology and tight junction protein expressions. Therefore, it can be concluded that dietary B. subtilis A and B could be used as alternatives to synthetic antibiotics in the promotion of gut health and productivity index in broiler production.

Effects of Dietary Ginsenoside Rg1 Supplementation on Growth Performance, Gut Health, and Serum Immunity in Broiler Chickens

The restriction and banning of antibiotics in farm animal feed has led to a search for promising substitutes for antibiotics to promote growth and maintain health for livestock and poultry. Ginsenoside Rg1, which is one of the most effective bioactive components in ginseng, has been reported to have great potential to improve the anti-inflammatory and anti-oxidative status of animals. In this study, 360 Chinese indigenous broiler chickens with close initial body weight were divided into 5 groups. Each group contained 6 replicates and each replicate had 12 birds. The experimental groups were: the control group, fed with the basal diet; the antibiotic group, fed basal diet + 300 mg/kg 15% chlortetracycline; and three Rg1 supplementation groups, fed with basal diet + 100, 200, and 300 mg/kg ginsenoside Rg1, respectively. The growth performance, immune function, and intestinal health of birds were examined at early (day 1-28) and late (day 29-51) stages. Our results showed that dietary supplementation of 300 mg/kg ginsenoside Rg1 significantly improved the growth performance for broilers, particularly at the late stage, including an increase in final body weight and decrease of feed conversion ratio (P < 0.05). Additionally, the integrity of intestinal morphology (Villus height, Crypt depth, and Villus height/Crypt depth) and tight junction (ZO-1 and Occludin), and the secretion of sIgA in the intestine were enhanced by the supplementation of Rg1 in chicken diet (P < 0.05). The immune organ index showed that the weight of the thymus, spleen, and bursa was significantly increased at the early stage in ginsenoside Rg1 supplementation groups (P < 0.05). Our findings might demonstrate that ginsenoside Rg1 could serve as a promising antibiotic alternative to improve the growth performance and gut health for broiler chickens mainly through its amelioration of inflammatory and oxidative activities.

Progress on Gut Health Maintenance and Antibiotic Alternatives in Broiler Chicken Production

The perturbation of gut health is a common yet unresolved problem in broiler chicken production. Antibiotics used as growth promoters have remarkably improved the broiler production industry with high feed conversion efficiency and reduced intestinal problems. However, the misuse of antibiotics has also led to the increase in the development of antibiotic resistance and antibiotic residues in the meat. Many countries have enacted laws prohibiting the use of antibiotics in livestock production because of the increasing concerns from the consumers and the public. Consequently, one of the most significant discussions in the poultry industry is currently antibiotic-free livestock production. However, the biggest challenge in animal husbandry globally is the complete removal of antibiotics. The necessity to venture into antibiotic-free production has led researchers to look for alternatives to antibiotics in broiler chicken production. Many strategies can be used to replace the use of antibiotics in broiler farming. In recent years, many studies have been conducted to identify functional feed additives with similar beneficial effects as antibiotic growth promoters. Attention has been focused on prebiotics, probiotics, organic acids, emulsifiers, enzymes, essential oils, tributyrin, and medium-chain fatty acids. In this review, we focused on recent discoveries on gut health maintenance through the use of these functional feed additives as alternatives to antibiotics in the past 10 years to provide novel insights into the design of antibiotic-free feeds.

Gastrointestinal Development and Microbiota Responses of Geese to Honeycomb Flavonoids Supplementation

Background: Geese are conventionally considered to be herbivorous, which could also be raised with concentrate feeding diets without green grass because of the similar gastrointestinal tract with other poultry. However, the geese gut microbiota profiles and their interactions with epithelial cells are still of limited study. Flavonoids were well-documented to shape gut microbiota and promote epithelial barrier functions individually or cooperatively with other metabolites. Therefore, in the present study, honeycomb flavonoids (HF) were supplemented to investigate the effects on growth performances, intestinal development, and gut microbiome of geese.

Material and Methods: A total of 400 1-day-old male lion-head geese with similar birth weight (82.6 ± 1.4 g) were randomly divided into five treatments: the control treatment (CON) and the HF supplementation treatments, HF was supplemented arithmetically to increase from 0.25 to 1%. Growth performance, carcass performances, and intestines' development parameters were measured to determine the optimum supplement. Junction proteins including ZO-1 and ZO-2 and cecal microbiota were investigated to demonstrate the regulatory effects of HF on both microbiota and intestinal epithelium.

Results: Results showed that 0.5% of HF supplement had superior growth performance, carcass performance, and the total parameters of gastrointestinal development to other treatments. Further research showed that tight junction proteins including ZO-1 and ZO-2 significantly up-regulated, while Firmicutes and some probiotics including Clostridiales, Streptococcus, Lachnoclostridium, and Bifidobacterium, remarkably proliferated after HF supplement. In conclusion, HF supplement in concentrate-diet feeding geese effectively increased the growth performances by regulating the gut microbiota to increase the probiotic abundance to promote the nutrient digestibility and fortify the epithelial development and barrier functions to facilitate the nutrient absorption and utilization.

Effects of Selenium Conjugated to Insect Protein on Pharmacokinetics of Florfenicol and Enrofloxacin in Laying Hens

In the context of increasing awareness on the dietary supplementation of organic selenium in commercial poultry production and ensuring safe egg production, the present study investigated the effects of selenium on the pharmacokinetics of the therapeutic use of florfenicol and enrofloxacin from perspectives of laying performance, selenium deposition in eggs, and drug residue in plasma, organs, and eggs. A 2 × 3 factorial arrangement with two kinds of drugs (florfenicol vs. enrofloxacin, 200 mg/kg) and three levels of dietary organic selenium SCIP (selenium conjugated to insect protein) (0, 2, and 5 mg/kg) was designed together with a blank control group. Healthy Hy-Line Brown laying hens (n = 252, 40-week-old and 90.0 ± 1.7% of egg production rate) were randomly allocated into one of seven treatments with six replicates and six hens per replicate. The experiment lasted for 42 days and consisted of three periods (adjusted stage, depositional stage, and eliminating stage) of 14 days each. These stages entail feeding of the laying hens with basal diets, addition of drugs and selenium synchronously into the diets, drug withdrawal from diet, and supply of selenium uninterruptedly in the diet. Egg production and feed intake were recorded on daily and weekly bases, respectively. The selenium content in egg yolk, egg white, and whole eggs and the drug residues in eggs, plasma, liver, kidney, and breast muscle were determined on days 2, 3, 5, 6, 7, 9, 11, and 14 of the depositional and eliminating stages. There was no significant difference (p > 0.05) in egg production among the dietary treatments, but feed intake decreased significantly (p < 0.05) in the drug treatment group compared to other groups. Dietary organic selenium decreased the residue of drugs in tissues and eggs, while the metabolism and deposition of selenium in laying hens were suppressed due to drug effects. The results of the present study are of significance to enrich the knowledge of the pharmacokinetics of florfenicol and enrofloxacin in laying hens and ensure the quality of poultry products.

Biological Function of Short-Chain Fatty Acids and Its Regulation on Intestinal Health of Poultry

Short-chain fatty acids (SCFAs) are metabolites generated by bacterial fermentation of dietary fiber (DF) in the hindgut. SCFAs are mainly composed of acetate, propionate and butyrate. Many studies have shown that SCFAs play a significant role in the regulation of intestinal health in poultry. SCFAs are primarily absorbed from the intestine and used by enterocytes as a key substrate for energy production. SCFAs can also inhibit the invasion and colonization of pathogens by lowering the intestinal pH. Additionally, butyrate inhibits the expression of nitric oxide synthase (NOS), which encodes inducible nitric oxide synthase (iNOS) in intestinal cells via the PPAR-γ pathway. This pathway causes significant reduction of iNOS and nitrate, and inhibits the proliferation of Enterobacteriaceae to maintain overall intestinal homeostasis. SCFAs can enhance the immune response by stimulating cytokine production (e.g. TNF-α, IL-2, IL-6, and IL-10) in the immune cells of the host. Similarly, it has been established that SCFAs promote the differentiation of T cells into T regulatory cells (Tregs) and expansion by binding to receptors, such as Toll-like receptors (TLR) and G protein-coupled receptors (GPRs), on immune cells. SCFAs have been shown to repair intestinal mucosa and alleviate intestinal inflammation by activating GPRs, inhibiting histone deacetylases (HDACs), and downregulating the expression of pro-inflammatory factor genes. Butyrate improves tight-junction-dependent intestinal barrier function by promoting tight junction (TJ) assembly. In recent years, the demand for banning antibiotics has increased in poultry production. Therefore, it is extremely important to maintain the intestinal health and sustainable production of poultry. Taking nutrition strategies is important to regulate SCFA production by supplementing dietary fiber and prebiotics, SCFA-producing bacteria (SPB), and additives in poultry diet. However, excessive SCFAs will lead to the enteritis in poultry production. There may be an optimal level and proportion of SCFAs in poultry intestine, which benefits to gut health of poultry. This review summarizes the biological functions of SCFAs and their role in gut health, as well as nutritional strategies to regulate SCFA production in the poultry gut.

Effects of Adding Eubiotic Lignocellulose on the Growth Performance, Laying Performance, Gut Microbiota, and Short-Chain Fatty Acids of Two Breeds of Hens

Eubiotic lignocellulose is a new and useful dietary fiber source for chickens. However, few studies have been undertaken on the impacts of its use as a supplement in different chicken breeds. In this experiment, 108 Chinese native breed Bian hens (BH) and 108 commercial breed ISA Brown hens (IBH) were chosen. They were randomly divided into three groups, and 0, 2, or 4% eubiotic lignocellulose was added to their feed during the growing periods (9-20 weeks), respectively. We aimed to observe the impacts of adding eubiotic lignocellulose on the growth and laying performance, gut microbiota, and short-chain fatty acid (SCFA) of two breeds of hens. In this study, the addition of eubiotic lignocellulose had no significant effect on the growth performance and gut microbial diversity in the two breeds of chickens (P > 0.05). Compared with the control group, adding 4% eubiotic lignocellulose significantly increased the cecum weight, laying performance (P < 0.05), but had no significant effect on the SCFA of BH (P > 0.05); however, adding 4% significantly inhibited the intestinal development, laying performance, butyrate concentration, and SCFA content of IBH (P < 0.05). Moreover, the relative abundances of the fiber-degrading bacteria Alloprevotella and butyrate-producing bacteria Fusobacterium in the 4% group of BH were significantly higher than those in the 4% group of IBH (P < 0.05), resulting in the concentration of butyrate was significantly higher than those in it (P < 0.05). Combining these results suggests that the tolerance of BH to a high level of eubiotic lignocellulose is greater than that of IBH and adding 2-4% eubiotic lignocellulose is appropriate for BH, while 0-2% eubiotic lignocellulose is appropriate for IBH.

The Spatial and Temporal Characterization of Gut Microbiota in Broilers

The gut microbiota of chickens plays an important role in host physiology. However, the colonization and prevalence of gut microbiota have not been well-characterized. Here, we performed 16S rRNA gene sequencing on the duodenal, cecal and fecal microbiota of broilers at 1, 7, 21, and 35 days of age and characterized the dynamic succession of microbiota across the intestinal tract. Our results showed that Firmicutes was the most abundant phylum detected in each gut site at various ages, while the microbial diversity and composition varied among the duodenum, cecum, and feces at different ages. The microbial diversity and complexity of the cecal microbiota increased with age, gradually achieving stability at 21 days of age. As a specific genus in the cecum, Clostridium_sensu_stricto_1 accounted for 83.50% of the total abundance at 1 day of age, but its relative abundance diminished with age. Regarding the feces, the highest alpha diversity was observed at 1 day of age, significantly separated from the alpha diversity of other ages. In addition, no significant differences were observed in the alpha diversity of duodenal samples among 7, 21, and 35 days of age. The predominant bacterium, Lactobacillus, was relatively low (0.68–6.04%) in the intestinal tract of 1-day-old chicks, whereas its abundance increased substantially at 7 days of age and was higher in the duodenum and feces. Escherichia-Shigella, another predominant bacterium in the chicken intestinal tract, was also found to be highly abundant in fecal samples, and the age-associated dynamic trend coincided with that of Lactobacillus. In addition, several genera, including Blautia, Ruminiclostridium_5, Ruminococcaceae_UCG-014, and [Ruminococcus]_torques_group, which are related to the production of short-chain fatty acids, were identified as biomarker bacteria of the cecum after 21 days of age. These findings shed direct light on the temporal and spatial dynamics of intestinal microbiota and provide new opportunities for the improvement of poultry health and production.

Folic Acid Absorption Characteristics and Effect on Cecal Microbiota of Laying Hens

This experiment was conducted to investigate the characteristics of folic acid (FA) absorption in laying hens and the effect of FA supplementation on cecal microbiota. A total of 432 healthy hens (30-week-old) were randomly assigned to four diets supplemented with FA: 0, 1, 6, and 24 mg/kg of feed for 8 w. Blood, duodenum, jejunum, ileum, cecum, and cecal chyme samples (six samples per treatment) were collected from the hens at the end of the feeding trial. Expression profiles of folate transport and transformation genes in intestine and cecal microbiota were detected. Results showed that serum folate level significantly increased (P < 0.01) with an increase in dietary FA supplementation, reaching a plateau at 6 mg/kg FA supplementation. The expression of FA transport and transformation genes was not affected in the cecum (P > 0.05) by dietary FA supplementation; however, it was affected in the duodenum, jejunum, and ileum and mostly showed a downward trend in treatment groups (P < 0.05). The genes affected include duodenal folate receptor (Folr) and dihydrofolate reductase (Dhfr), jejunal proton-coupled folate transporter (Pcft) and reduced folate carrier (Rfc), and ileal ATP binding cassette subfamily C member (Abcc2), Abcc3, Rfc, Folr, and Dhfr. Furthermore, according to the operational taxonomic unit classification and taxonomic position identification, the cecal microbiota population of the hens was not affected by dietary FA supplementation at the phylum, class, order, family, genus, and species levels (P > 0.05). However, the relative abundance of some microbiota was affected by dietary FA supplementation (P < 0.05). In conclusion, FA transport from the intestinal lumen into enterocytes, and then into the bloodstream, is strictly regulated, which may be associated with the regulation of the expression profiles of genes involved in FA absorption. Pathogenic bacteria decreased in the cecum, especially at 24 mg/kg supplementation, but the beneficial bacteria (Bifidobacteriaceae) decreased at this level, too. Overall, FA supplementation at 6 mg/kg, which was selected for folate-enriched egg production, did not affect the health and metabolism of laying hens negatively.

Persistent Purine Metabolic Abnormality Induces the Aggravation of Visceral Inflammation and Intestinal Microbiota Dysbiosis in Magang Goose

Gout is a disease involving abnormal purine metabolism that is widespread in mammals and birds. Goose is especially susceptible for gout in early stage. However, a few studies investigated the ontogenetic pattern of goslings with purine metabolic abnormality. Our studies were conducted to investigate whether persistent purine metabolic abnormality would lead to aggravation of visceral inflammation and intestinal microbiota dysbiosis in goose. A total of 132 1-day-old Magang geese were randomly divided into six replicates and fed a high-calcium and protein meal-based diet from 1 to 28 days. The experiment lasted for 28 days. Liver and kidney damages were observed in 14- and 28-day-old Magang geese, and liver inflammation increased with increasing age. In 28-day-old Magang geese, serum CAT and liver GSH-Px activity were significantly reduced. Furthermore, jejunum intestinal barrier was impaired and the abundance of Bacteroides was significantly reduced at the genus level. Collectively, the high-calcium and high-protein (HCP) meal-based diet caused liver and kidney damage in 28-day-old Magang geese, leading to hyperuricemia and gout symptoms, and the intestinal barrier is impaired and the intestinal flora is disrupted.

Stimulation of Toll-Like Receptor 3 Diminishes Intracellular Growth of Salmonella Typhimurium by Enhancing Autophagy in Murine Macrophages

The Salmonella enterica serovar Typhimurium (S. Typhimurium) is a facultative Gram-negative bacterium that causes acute gastroenteritis and food poisoning. S. Typhimurium can survive within macrophages that are able to initiate the innate immune response after recognizing bacteria via various pattern-recognition receptors (PRRs), such as Toll-like receptors (TLRs). In this study, we investigated the effects and molecular mechanisms by which agonists of endosomal TLRs—especially TLR3—contribute to controlling S. Typhimurium infection in murine macrophages. Treatment with polyinosinic:polycytidylic acid (poly(I:C))—an agonist of TLR3—significantly suppressed intracellular bacterial growth by promoting intracellular ROS production in S. Typhimurium-infected cells. Pretreatment with diphenyleneiodonium (DPI)—an NADPH oxidase inhibitor—reduced phosphorylated MEK1/2 levels and restored intracellular bacterial growth in poly(I:C)-treated cells during S. Typhimurium infection. Nitric oxide (NO) production increased through the NF-κB-mediated signaling pathway in poly(I:C)-treated cells during S. Typhimurium infection. Intracellular microtubule-associated protein 1A/1B-light chain 3 (LC3) levels were increased in poly(I:C)-treated cells; however, they were decreased in cells pretreated with 3-methyladenine (3-MA)—a commonly used inhibitor of autophagy. These results suggest that poly(I:C) induces autophagy and enhances ROS production via MEK1/2-mediated signaling to suppress intracellular bacterial growth in S. Typhimurium-infected murine macrophages, and that a TLR3 agonist could be developed as an immune enhancer to protect against S. Typhimurium infection.

How Early-Life Gut Microbiota Alteration Sets Trajectories for Health and Inflammatory Bowel Disease?

Inflammatory bowel disease (IBD) is a recurrent chronic inflammatory condition of the intestine without any efficient therapeutic regimens. Gut microbiota, which plays an instrumental role in the development and maturation of the immune system, has been implicated in the pathogenesis of IBD. Emerging evidence has established that early-life events particularly maternal influences and antibiotic treatment are strongly correlated with the health or susceptibility to disease of an individual in later life. Thus, it is proposed that there is a critical period in infancy, during which the environmental exposures bestow a long-term pathophysiological imprint. This notion sheds new light on the development of novel approaches for the treatment, i.e., early interventions, more precisely, the prevention of many uncurable chronic inflammatory diseases like IBD. In this review, we have integrated current evidence to describe the feasibility of the “able-to-be-regulated microbiota,” summarized the underlying mechanisms of the “microbiota-driven immune system education,” explored the optimal intervention time window, and discussed the potential of designing early-probiotic treatment as a new prevention strategy for IBD.

Salmonella spvC Gene Inhibits Autophagy of Host Cells and Suppresses NLRP3 as Well as NLRC4

Salmonella spvC gene, encoding a phosphothreonine lyase on host mitogen-activated protein kinases, facilitates systemic infection of Salmonella while the precise mechanisms remain elusive. Autophagy and pyroptosis dependent on the activation of inflammasomes, as parts of innate immune response, contribute to host defense against Salmonella infection. Recently, we reported that spvC could inhibit pyroptosis. To explore the effect of spvC on autophagy and the relationship between its function in pyroptosis and autophagy, infection models of macrophages J774A.1 and epithelial HeLa cells co-cultured with Salmonella Typhimurium wild type, spvC deletion, site-directed mutant which lacks phosphothreonine lyase activity, or complemented strain were established. The levels of LC3 turnover and Beclin 1 of J774A.1 cells were determined by western blot. Confocal laser scanning microscopy was used to visualize the autophagic flux after being transfected with mRFP-GFP-LC3 plasmid in HeLa cells. Results showed that SpvC inhibited autophagosome formation through its phosphothreonine lyase activity. Additionally, analysis of nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain-containing 3 (NLRP3) and NLR with CARD domain-containing 4 (NLRC4) in J774A.1 cells indicated that spvC decreased the protein levels of NLRP3 and NLRC4, which were significantly changed by autophagy inhibitor Bafilomycin A1. Together, our observations reveal a novel mechanism of spvC in Salmonella pathogenesis and host inflammatory response via inhibiting autophagy and NLRP3 as well as NLRC4. These pathways and their subversion by diverse pathogen virulence determinants are expected to throw light on the design of anti-infective agents.

Making the Most of the Host; Targeting the Autophagy Pathway Facilitates Staphylococcus aureus Intracellular Survival in Neutrophils

The success of Staphylococcus aureus as a human commensal and an opportunistic pathogen relies on its ability to adapt to several niches within the host. The innate immune response plays a key role in protecting the host against S. aureus infection; however, S. aureus adeptness at evading the innate immune system is indisputably evident. The “Trojan horse” theory has been postulated to describe a mechanism by which S. aureus takes advantage of phagocytes as a survival niche within the host to facilitate dissemination of S. aureus to secondary sites during systemic infection. Several studies have determined that S. aureus can parasitize both professional and non-professional phagocytes by manipulating the host autophagy pathway in order to create an intracellular survival niche. Neutrophils represent a critical cell type in S. aureus infection as demonstrated by the increased risk of infection among patients with congenital neutrophil disorders. However, S. aureus has been repeatedly shown to survive intracellularly within neutrophils with evidence now supporting a pathogenic role of host autophagy. By manipulating this pathway, S. aureus can also alter the apoptotic fate of the neutrophil and potentially skew other important signalling pathways for its own gain. Understanding these critical host-pathogen interactions could lead to the development of new host directed therapeutics for the treatment of S. aureus infection by removing its intracellular niche and restoring host bactericidal functions. This review discusses the current findings surrounding intracellular survival of S. aureus within neutrophils, the pathogenic role autophagy plays in this process and considers the therapeutic potential for targeting this immune evasion mechanism.

Anaplasmataceae: Dichotomous Autophagic Interplay for Infection

Autophagy is a vital conserved degradative process that maintains cellular homeostasis by recycling or eliminating dysfunctional cellular organelles and proteins. More recently, autophagy has become a well-recognized host defense mechanism against intracellular pathogens through a process known as xenophagy. On the host-microbe battlefield many intracellular bacterial pathogens have developed the ability to subvert xenophagy to establish infection. Obligately intracellular bacterial pathogens of the Anaplasmataceae family, including Ehrlichia chaffeensis, Anaplasma phaogocytophilium and Orientia tsutsugamushi have developed a dichotomous strategy to exploit the host autophagic pathway to obtain nutrients while escaping lysosomal destruction for intracellular survival within the host cell. In this review, the recent findings regarding how these master manipulators engage and inhibit autophagy for infection are explored. Future investigation to understand mechanisms used by Anaplasmataceae to exploit autophagy may advance novel antimicrobial therapies and provide new insights into how intracellular microbes exploit autophagy to survive.

Autophagy-A Story of Bacteria Interfering with the Host Cell Degradation Machinery

Autophagy is a highly conserved and fundamental cellular process to maintain cellular homeostasis through recycling of defective organelles or proteins. In a response to intracellular pathogens, autophagy further acts as an innate immune response mechanism to eliminate pathogens. This review will discuss recent findings on autophagy as a reaction to intracellular pathogens, such as Salmonella typhimurium, Listeria monocytogenes, Mycobacterium tuberculosis, Staphylococcus aureus, and pathogenic Escherichia coli. Interestingly, while some of these bacteria have developed methods to use autophagy for their own benefit within the cell, others have developed fascinating mechanisms to evade recognition, to subvert the autophagic pathway, or to escape from autophagy.

Autophagy and Lc3-Associated Phagocytosis in Zebrafish Models of Bacterial Infections

Modeling human infectious diseases using the early life stages of zebrafish provides unprecedented opportunities for visualizing and studying the interaction between pathogens and phagocytic cells of the innate immune system. Intracellular pathogens use phagocytes or other host cells, like gut epithelial cells, as a replication niche. The intracellular growth of these pathogens can be counteracted by host defense mechanisms that rely on the autophagy machinery. In recent years, zebrafish embryo infection models have provided in vivo evidence for the significance of the autophagic defenses and these models are now being used to explore autophagy as a therapeutic target. In line with studies in mammalian models, research in zebrafish has shown that selective autophagy mediated by ubiquitin receptors, such as p62, is important for host resistance against several bacterial pathogens, including Shigella flexneri, Mycobacterium marinum, and Staphylococcus aureus. Furthermore, an autophagy related process, Lc3-associated phagocytosis (LAP), proved host beneficial in the case of Salmonella Typhimurium infection but host detrimental in the case of S. aureus infection, where LAP delivers the pathogen to a replication niche. These studies provide valuable information for developing novel therapeutic strategies aimed at directing the autophagy machinery towards bacterial degradation.