Host metabolic shift during systemic Salmonella infection revealed by comparative proteomics

Bacterial metabolism in the host and its association with virulence

The host restricted pathogens are competently dependent on their respective host for nutritional requirements. The bacterial metabolic pathways are surprisingly varied and remarkably flexible that in turn help them to successfully overcome competition and colonise their host. The metabolic adaptation plays pivotal role in bacterial pathogenesis. The understanding of host-pathogen metabolic crosstalk needs to be prioritized to decipher host-pathogen interactions. The review focuses on various aspects of host pathogen interactions that majorly involves adaptation of bacterial metabolism to counteract immune mechanisms by rectifying metabolic cues that provides pathogen the idea of different anatomical sites and the local physiology of the host. The key set of metabolites that are recognized as centre of competition between host and its pathogens are also briefly discussed. The factors that control the timely expression of virulence of bacterial pathogens is poorly understood. The perspective presented herein will facilitate us with a broader view of molecular mechanisms that modulates the expression of virulence factors in bacterial pathogens. The knowledge of crosslinked metabolic pathways of bacteria and their host will serve to develop novel potential therapeutics.

ZnO-Cu/Mn nanozyme for rescuing the intestinal homeostasis in Salmonella-induced colitis

Salmonella is one of the most common foodborne pathogens, which can cause severe enteritis and intestinal microbiota imbalance. However, there are limited strategies currently available for preventing or treating Salmonella-induced colitis. Herein, we developed the Cu/Mn-co-doped ZnO tandem nanozyme (ZnO-CM) with pH-responsive multienzyme-mimicking activities via doping engineering for the treatment of Salmonella-induced colitis. Benefiting from the co-doping of Cu and Mn, ZnO-CM nanospheres exhibit remarkable peroxidase-like activity in acidic condition and superoxide dismutase- and catalase-like activities in neutral environment. Animal experiments show that ZnO-CM can efficiently inhibit bacterial growth, alleviate inflammation, and restore the intestinal barrier, resulting in good antibacterial and anti-inflammatory effects on Salmonella-induced colitis. Mechanistically, ZnO-CM functions through inhibiting the continuous accumulation of ROS, increasing the levels of tight junction proteins occludin and claudin-1, and decreasing the expression of pro-inflammatory cytokines IL-1β and IL-6 in intestine. This work not only presents an effective paradigm for Salmonella-induced colitis therapy, but also provides new sights into the prevention and treatment of other bacterial enteritis.

Cinnamaldehyde Alleviates Salmonellosis in Chicks by Regulating Gut Health

Due to the high mortality rate in chicks caused by pullorum disease (PD) and the drawbacks of antibiotic resistance, the poultry industry is increasingly interested in using natural herbal antimicrobial agents as alternatives, with cinnamaldehyde (CA) being a focus due to its multitarget and synergistic effects. This study aimed to evaluate the effects of oral administration of CA on restoring intestinal physical integrity, intestinal microbial barrier, and intestinal metabolism in a laboratory model of Salmonella pullorum (S. pullorum) infection in chicks. Thirty-six chicks were divided into six groups. The S.P and CA groups were infected with 5 × 108 CFU/mL, 0.5 mL S. pullorum, while the CON group received an equal-volume saline injection. The CA group was treated with 100 mg/kg CA, and the others received phosphate buffer saline (PBS). Samples were collected 24 h after the last treatment. Intestinal physical integrity was assessed by H&E staining, and ELISA was used to measure inflammatory factors. In situ hybridization (ISH) and RT-qPCR were used to measure the expression of tight-junction protein mRNA. The microbiota was analyzed by 16S rRNA gene sequencing of the ileal contents, and metabolite analysis was performed on the intestinal contents. After CA treatment, the expression of IL-1β and TNF-α was reduced, and IL-10 was increased (p < 0.05). H&E staining showed that the intestinal structure was partially restored after treatment. ISH results showed that the fluorescence intensity indicating gene expression status was low in the S.P group and high in the CA group, indicating reduced intestinal permeability. RT-qPCR showed that CA up-regulated the mRNA expression of tight-junction proteins (claudin-1, occludin-1, and zo-1, p < 0.05). The 16S rRNA gene sequence analysis showed that Salmonella was significantly enriched in the S.P group (LDA score > 2.0, p < 0.05), while specific genera were significantly more abundant in the treated groups. Untargeted sequencing of intestinal contents showed that key metabolites (butyrate, alanine, glutamate, cholesterol, and propionate) in the CA group were significantly changed compared with the S.P group (p < 0.05). CA treatment was the most effective method for reducing PD intestinal colonization and maintaining better intestinal homeostasis, possibly by regulating intestinal microbiota and metabolic functions.

Salmonella: Infection mechanism and control strategies

Salmonella is a foodborne pathogen that predominantly resides in the intestinal tract of humans and animals. Infections caused by Salmonella can lead to various illnesses, including gastroenteritis, bacteremia, septicemia, and focal infections, with severe cases potentially resulting in host mortality. The mechanisms by which Salmonella invades host cells and disseminates throughout the body are partly understood, but there are still many scientific questions to be solved. This review aims to synthesize existing research on the interactions between Salmonella and hosts, detailing a comprehensive infection mechanism from adhesion and invasion to intracellular propagation and systemic spread. Overuse of antibiotics contributes to the emergence of drug-resistant Salmonella strains. An in-depth analysis of the mechanism of Salmonella infection will provide a theoretical basis for the development of novel Salmonella control strategies. These innovative control strategies include antibiotic adjuvants, small molecules, phages, attenuated vaccines, and probiotic therapies, which show huge potential in controlling Salmonella infection.

Establishment of a STING-Deficient HepG2 Cell Line through CRISPR/Cas9 System and Evaluation of Its Effects on Salmonella Replication

Background

Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) is a common food-borne pathogen that causes gastroenteritis and can lead to life-threatening systemic disease when it spreads to vital organs, such as the liver. Stimulator of interferon genes (STING) is a crucial regulator of the host's innate immune response to viral infections, while its role in bacterial infections remains controversial. This study aims to establish a STING-deficient HepG2 cell line through the CRISPR/Cas9 system and evaluate its effects on Salmonella replication.

Methods

In this study, a STING knockout HepG2 cell line was constructed through the application of CRISPR/Cas9 technology. We assessed cell viability and proliferation using the CCK-8 assay. Subsequently, we investigated the effect of STING deletion on Salmonella replication and the expression of type I interferon-related genes.

Results

The STING knockout HepG2 cell line was successfully constructed using the CRISPR/Cas9 system. The proliferation capability was diminished in STING-deficient HepG2 cells, while Salmonella Typhimurium replication in these cells was augmented compared to the wild-type (WT) group. Following Salmonella infection, the transcriptional responses of type I interferon-related genes, such as IFNB1 and ISG15, were inhibited in STING-deficient HepG2 cells.

Conclusions

We successfully constructed a STING-deficient cell line. Our finding of increased Salmonella Typhimurium replication in STING-deficient HepG2 cells provides the basis for further studies on pathogen-host interactions.

Proteome profiling identifies a link between the mitochondrial pathways and host-microbial sensor ELMO1 following Salmonella infection

The host EnguLfment and cell MOtility protein 1 (ELMO1) is a cytosolic microbial sensor that facilitates bacterial sensing, internalization, clearance, and inflammatory responses. We have shown previously that ELMO1 binds bacterial effector proteins, including pathogenic effectors from Salmonella and controls host innate immune signaling. To understand the ELMO1-regulated host pathways, we have performed liquid chromatography Multinotch MS3-Tandem Mass Tag (TMT) multiplexed proteomics to determine the global quantification of proteins regulated by ELMO1 in macrophages during Salmonella infection. Comparative proteome analysis of control and ELMO1-depleted murine J774 macrophages after Salmonella infection quantified more than 7000 proteins with a notable enrichment in mitochondrial-related proteins. Gene ontology enrichment analysis revealed 19 upregulated and 11 downregulated proteins exclusive to ELMO1-depleted cells during infection, belonging to mitochondrial functions, metabolism, vesicle transport, and the immune system. By assessing the cellular energetics via Seahorse analysis, we found that Salmonella infection alters mitochondrial metabolism, shifting it from oxidative phosphorylation to glycolysis. Importantly, these metabolic changes are significantly influenced by the depletion of ELMO1. Furthermore, ELMO1 depletion resulted in a decreased ATP rate index following Salmonella infection, indicating its importance in counteracting the effects of Salmonella on immunometabolism. Among the proteins involved in mitochondrial pathways, mitochondrial fission protein DRP1 was significantly upregulated in ELMO1-depleted cells and in ELMO1-KO mice intestine following Salmonella infection. Pharmacological Inhibition of DRP1 revealed the link of the ELMO1-DRP1 pathway in regulating the pro-inflammatory cytokine TNF-α following infection. The role of ELMO1 has been further characterized by a proteome profile of ELMO1-depleted macrophage infected with SifA mutant and showed the involvement of ELMO1-SifA on mitochondrial function, metabolism and host immune/defense responses. Collectively, these findings unveil a novel role for ELMO1 in modulating mitochondrial functions, potentially pivotal in modulating inflammatory responses.

Significance Statement

Host microbial sensing is critical in infection and inflammation. Among these sensors, ELMO1 has emerged as a key regulator, finely tuning innate immune signaling and discriminating between pathogenic and non-pathogenic bacteria through interactions with microbial effectors like SifA of Salmonella . In this study, we employed Multinotch MS3-Tandem Mass Tag (TMT) multiplexed proteomics to determine the proteome alterations mediated by ELMO1 in macrophages following WT and SifA mutant Salmonella infection. Our findings highlight a substantial enrichment of host proteins associated with metabolic pathways and mitochondrial functions. Notably, we validated the mitochondrial fission protein DRP1 that is upregulated in ELMO1-depleted macrophages and in ELMO1 knockout mice intestine after infection. Furthermore, we demonstrated that Salmonella -induced changes in cellular energetics are influenced by the presence of ELMO1. This work shed light on a possible novel link between mitochondrial dynamics and microbial sensing in modulating immune responses.

Exopolysaccharide secreted by Lactiplantibacillus plantarum Y12 showed inhibitory effect on the pathogenicity of Shigella flexneri in vitro and in vivo

Shigella flexneri is a prevalent foodborne and waterborne pathogen that threatens human health. Our previous research indicated that the Lactiplantibacillus plantarum Y12 exopolysaccharide (L-EPS) potentially inhibited the pathogenicity of S. flexneri. The in vitro results of this study demonstrated that L-EPS effectively mitigated the symptoms induced by S. flexneri in HT-29 cells, including inhibited gene expression levels of IL-1β, IL-6, IL-8, TNF-α, TLR 2/4, and NOD1/2; decreased apoptosis ratio; and alleviated damage degree of intestinal barrier function (Zona occludens 1, Occludin, and Claudin-1). The in vivo results demonstrated that S. flexneri treated with L-EPS elicited mild adverse physiological manifestations, an inflammatory response, and tissue damage. The infection of S. flexneri caused significant alterations in the abundance of phylum (Firmicutes, Bacteroidota, Actinobacteriota, and Proteobacteria), family (Lachnospiraceae, Muribaculaceae, Rikenellaceae, Prevotellaceaea, Ruminococcaceae, and Lactobaillaceae), and genus (Escherichia Shigella and Lachnospirillaceae NK4A136 group) within the cecal microbiota. These changes were accompanied by perturbations in taurine and hypotaurine metabolism, tricarboxylic acid (TCA) cycle activity, arginine biosynthesis, and histidine metabolic pathways. However, intervention with L-EPS attenuated the dysbiosis of cecal microbiota and metabolic disturbances. In summary, our research suggested a potential application of L-EPS as a functional food additive for mitigating S. flexneri infection.

Metabolism Shapes Immune Responses to Staphylococcus aureus

BACKGROUND

Staphylococcus aureus (S. aureus) is a common cause of hospital- and community-acquired infections that can result in various clinical manifestations ranging from mild to severe disease. The bacterium utilizes different combinations of virulence factors and biofilm formation to establish a successful infection, and the emergence of methicillin- and vancomycin-resistant strains introduces additional challenges for infection management and treatment.

SUMMARY

Metabolic programming of immune cells regulates the balance of energy requirements for activation and dictates pro- versus anti-inflammatory function. Recent investigations into metabolic adaptations of leukocytes and S. aureus during infection indicate that metabolic crosstalk plays a crucial role in pathogenesis. Furthermore, S. aureus can modify its metabolic profile to fit an array of niches for commensal or invasive growth.

KEY MESSAGES

Here we focus on the current understanding of immunometabolism during S. aureus infection and explore how metabolic crosstalk between the host and S. aureus influences disease outcome. We also discuss how key metabolic pathways influence leukocyte responses to other bacterial pathogens when information for S. aureus is not available. A better understanding of how S. aureus and leukocytes adapt their metabolic profiles in distinct tissue niches may reveal novel therapeutic targets to prevent or control invasive infections.

M2 Polarization and Inhibition of Host Cell Glycolysis Contributes Intracellular Survival of Salmonella Strains in Chicken Macrophage HD-11 Cells

Salmonella enterica is a group of facultative, gram-negative bacteria. Recently, new evidence indicated that Salmonella could reprogram the host metabolism to increase energy or metabolites available for intracellular replication. In this study, using a chicken-specific kinomic immunometabolism peptide array analysis, we found that infection by S. Enteritidis induced significant phosphorylation changes in many key proteins of the glycolytic pathway in chicken macrophage HD-11 cells, indicating a shift in glycolysis caused by Salmonella infection. Nitric oxide production and changes of glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) represented by extracellular acidification rate (ECAR) and oxygen consumption rate (OCR), respectively, were measured in chicken macrophages infected with three Salmonella strains (S. Enteritidis, S. Heidelberg, and S. Senftenberg). The infection reduced glycolysis and enhanced OXPHOS in chicken macrophages as indicated by changes of ECAR and OCR. Salmonella strains differentially affected macrophage polarization and glycolysis. Among three strains tested, S. Enteritidis was most effective in downregulating glycolysis and promoting M2 polarization as measured by ECAR, ORC, and NO production; while S. Senftenberg did not alter glycolysis and may promote M1 polarization. Our results suggested that downregulation of host cell glycolysis and increase of M2 polarization of macrophages may contribute to increased intracellular survival of S. Enteritidis.

Extracellular vesicle-mediated regulation of macrophage polarization in bacterial infections

Extracellular vesicles (EVs) are nanoscale membrane-enveloped vesicles secreted by prokaryotic and eukaryotic cells, which are commonly defined as membrane vesicles (MVs) and exosomes, respectively. They play critical roles in the bacteria-bacteria and bacteria-host interactions. In infectious diseases caused by bacteria, as the first line of defense against pathogens, the macrophage polarization mode commonly determines the success or failure of the host's response to pathogen aggression. M1-type macrophages secrete pro-inflammatory factors that support microbicidal activity, while alternative M2-type macrophages secrete anti-inflammatory factors that perform an antimicrobial immune response but partially allow pathogens to replicate and survive intracellularly. Membrane vesicles (MVs) released from bacteria as a distinctive secretion system can carry various components, including bacterial effectors, nucleic acids, or lipids to modulate macrophage polarization in host-pathogen interaction. Similar to MVs, bacteria-infected macrophages can secrete exosomes containing a variety of components to manipulate the phenotypic polarization of "bystander" macrophages nearby or long distance to differentiate into type M1 or M2 to regulate the course of inflammation. Exosomes can also repair tissue damage associated with the infection by upregulating the levels of anti-inflammatory factors, downregulating the pro-inflammatory factors, and regulating cellular biological behaviors. The study of the mechanisms by which EVs modulate macrophage polarization has opened new frontiers in delineating the molecular machinery involved in bacterial pathogenesis and challenges in providing new strategies for diagnosis and therapy.

The successful use of -omic technologies to achieve the 'One Health' concept in meat producing animals

Human health and wellbeing are closely linked to healthy domestic animals, a vital wildlife, and an intact ecosystem. This holistic concept is referred to as 'One Health'. In this review, we provide an overview of the potential and the challenges for the use of modern -omics technologies, especially transcriptomics and proteomics, to implement the 'One Health' idea for food-producing animals. These high-throughput studies offer opportunities to find new potential molecular biomarkers to monitor animal health, detect pharmacological interventions and evaluate the wellbeing of farm animals in modern intensive livestock systems.