Commensal microbes provide first line defense against Listeria monocytogenes infection

Comparing Campylobacter jejuni to three other enteric pathogens in OligoMM12 mice reveals pathogen-specific host and microbiota responses

Campylobacter jejuni, non-typhoidal Salmonella spp., Listeria monocytogenes and enteropathogenic/enterohemorrhagic Escherichia coli (EPEC/EHEC) are leading causes of food-borne illness worldwide. Citrobacter rodentium has been used to model EPEC and EHEC infection in mice. The gut microbiome is well-known to affect gut colonization and host responses to many food-borne pathogens. Recent progress has established gnotobiotic mice as valuable models to study how microbiota affect the enteric infections by S. Typhimurium, C. rodentium and L. monocytogenes. However, for C. jejuni, we are still lacking a suitable gnotobiotic mouse model. Moreover, the limited comparability of data across laboratories is often negatively affected by variations between different research facilities or murine microbiotas. In this study, we applied the standardized gnotobiotic OligoMM12 microbiota mouse model and compared the infections in the same facility. We provide evidence of robust colonization and significant pathological changes in OligoMM12 mice following infection with these pathogens. Moreover, we offer insights into pathogen-specific host responses and metabolite signatures, highlighting the advantages of a standardized mouse model for direct comparisons of factors influencing the pathogenesis of major food-borne pathogens. Notably, we reveal for the first time that C. jejuni stably colonizes OligoMM12 mice, triggering inflammation. Additionally, our comparative approach successfully identifies pathogen-specific responses, including the detection of genes uniquely associated with C. jejuni infection in humans. These findings underscore the potential of the OligoMM12 model as a versatile tool for advancing our understanding of food-borne pathogen interactions.

Listeria monocytogenes gut interactions and listeriosis: Gut modulation and pathogenicity

Following ingestion via contaminated food, Listeria monocytogenes faces multiple hurdles through the human digestive system, thereby influencing its capacity to cause infection. This review provides a comprehensive overview of the multifaceted mechanisms employed by L. monocytogenes to overcome gastrointestinal hurdles and interact with the host's microbiota, facing chemical and physical barriers such as saliva, stomach acidity, bile salts and mechanical clearance. Proposed evasion strategies will be highlighted, exploring the bacteriocins produced by L. monocytogenes, such as the well-described bacteriocin Listeriolysin S (LLS), a bacteriocin that inhibits inflammogenic species - Lmo2776, and a phage tail-like bacteriocin, monocin. The competitive dynamic interactions within the gut microbiota, as well as the modulation of microbiota composition and immune responses, will also be explored. Finally, the adhesion and invasion of the intestinal epithelium by L. monocytogenes is described, exploring the mechanism of pathogenesis, biofilm and aggregation capacities and other virulence factors. Unlike previous reviews that may focus on individual aspects of L. monocytogenes pathogenicity, this review offers a holistic perspective on the bacterium's ability to persist and cause infection, integrating information about survival strategies, including bacteriocin production, immune modulation, and virulence factors. By connecting recent findings on microbial interactions and infection dynamics, this review incorporates recent developments in the field and connects various lines of research that explore both host and microbial factors influencing infection outcomes.

Nano in Micro: Novel Concepts in Foodborne Pathogen Transmission and Pathogenesis

In this article, we highlight novel components of foodborne pathogens that influence their response, physiology, adaptation, and survival in the face of diverse stresses, and consequently have implications for their transmission in the food chain and their pathogenesis. Recent insights into the role of bacteriophages/prophages, bacterial extracellular vesicles, and bacterial microcompartments, which make up the emerging field we coined as "nano in micro," are presented, together with the role of understudied food-relevant substrates in pathogen fitness and virulence. These new insights also lead to reflections on generally adopted laboratory conditions in the long-standing research field of adaptive stress response in foodborne pathogens. In addition, selected examples of the impact of diet and microbiota on intestinal colonization and host invasion are discussed. A final section on risk assessment presents an overview of tools for (kinetic) data modeling and perspectives for the implementation of information derived from whole-genome sequencing, combined with advancements in dose-response models and exposure assessments.

Colonic goblet cell-associated antigen passages mediate physiologic and beneficial translocation of live gut bacteria in preweaning mice

Gut-resident microorganisms have time-limited effects in distant tissues during early life. However, the reasons behind this phenomenon are largely unknown. Here, using bacterial culture techniques, we show that a subset of live gut-resident bacteria translocate and disseminate to extraintestinal tissues (mesenteric lymph nodes and spleen) in preweaning (day of life 17), but not adult (day of life 35), mice. Translocation and dissemination in preweaning mice appeared physiologic as it did not induce an inflammatory response and required host goblet cells, the formation of goblet cell-associated antigen passages, sphingosine-1-phosphate receptor-dependent leukocyte trafficking and phagocytic cells. One translocating strain, Lactobacillus animalisWU, showed antimicrobial activity against the late-onset sepsis pathogen Escherichia coli ST69 in vitro, and its translocation was associated with protection from systemic sepsis in vivo. While limited in context, these findings challenge the idea that translocation of gut microbiota is pathological and show physiologic and beneficial translocation during early life.

Whole Genome Analysis of Pediococcus acidilactici XJ-24 and Its Role in Preventing Listeria monocytogenes ATCC® 19115TM Infection in C57BL/6 Mice

Background/Objectives: As probiotics gain prominence in the prevention and treatment of intestinal diseases, their protective effects against pathogens and influence on host health have drawn significant attention. This study investigates the genomic characteristics and functional potential of Pediococcus acidilactici XJ-24 (XJ-24) in the prevention of Listeria monocytogenes (LM) infection in mice. Methods/Results: Whole-genome analysis confirmed the safety and probiotic properties of XJ-24, including acid and bile salt tolerance, antimicrobial activity, and safety. In vivo, C57BL/6 mice challenges indicated that XJ-24 significantly reduced LM colonization, suppressed pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, IFN-γ), alleviated colon and spleen tissue damage, and maintained intestinal barrier integrity by upregulating tight junction proteins (Occludin, Claudin-1, ZO-1). Moreover, XJ-24 modulated gut microbiota composition by increasing beneficial taxa while reducing harmful bacteria. Correlation analysis highlighted a positive association between Lachnospiraceae and tight junction proteins. Conclusions: These findings demonstrate the potential of XJ-24 as a functional probiotic for preventing LM infection and provide a basis for further clinical exploration.

A genome-wide screen in ex vivo gallbladders identifies Listeria monocytogenes factors required for virulence in vivo

Listeria monocytogenes is a Gram-positive pathogen that causes the severe foodborne disease listeriosis. Following oral infection of the host, L. monocytogenes disseminates from the gastrointestinal tract to peripheral organs, including the gallbladder, where it replicates to high densities, establishing the gallbladder as the primary bacterial reservoir. Despite its importance in pathogenesis, little is known about how L. monocytogenes survives and replicates in the gallbladder. In this study, we assessed the L. monocytogenes genes required for growth and survival in ex vivo non-human primate gallbladders using a transposon sequencing approach. The screen identified 43 genes required for replication in the gallbladder, some of which were known to be important for virulence, and others had not been previously studied in the context of infection. We evaluated the roles of 19 genes identified in our screen both in vitro and in vivo, and demonstrate that most were required for replication in bile in vitro, for intracellular infection of murine cells in tissue culture, and for virulence in an oral murine model of listeriosis. Interestingly, strains lacking the mannose and glucose phosphoenolpyruvate-dependent phosphotransferase system (PTS) permeases Mpt and Mpo exhibited no defects in intracellular growth or intercellular spread, but were significantly attenuated during murine infection. While the roles of PTS systems in vivo were not previously appreciated, these results suggest that PTS permeases are necessary for extracellular replication during infection. Overall, this study demonstrates that L. monocytogenes genes required for replication in the gallbladder also play broader roles in disease.

Increased Risk of Inflammatory Bowel Disease Among Patients With Nontyphoidal Salmonella Infections: A Population-Based Cohort Study

BACKGROUND

Despite the known association between microorganisms and development of inflammatory bowel disease (IBD), the role of nontyphoidal Salmonella (NTS) in IBD is not adequately addressed. We aimed at elucidating the relationship between NTS infection and the risk of IBD.

METHODS

Based on the National Health Insurance Research Database in Taiwan, this retrospective cohort study enrolled patients with NTS infection (exposure group; n = 4651) and those without NTS infection (comparator group; n = 4651) who were propensity score matched (1:1) by demographic data, medications, comorbidities, and index date. All patients were followed until IBD onset, individual mortality, or December 31, 2018. Cox proportional hazards regression analysis was performed to determine the hazard ratios and 95% confidence intervals (CIs). Sensitivity analyses were used for cross-validation.

RESULTS

The NTS group demonstrated an increased risk of IBD compared with the non-NTS groups (adjusted hazard ratio [aHR], 2.12; 95% CI, 1.62-2.78) with a higher risk of developing ulcerative colitis in the former (aHR, 2.27; 95% CI, 1.69-3.04). Nevertheless, the small sample size may contribute to lack of significant difference in Crohn's disease. Consistent findings were noted after excluding IBD diagnosed within 6 months of NTS infection (aHR, 2.28; 95% CI, 1.71-3.03), excluding those with enteritis/colitis before index date (aHR, 1.85; 95% CI, 1.28-2.68), excluding those using antibiotics for 1 month in the year before IBD onset (aHR, 1.81; 95% CI, 1.34-2.45), inverse probability of treatment weighting (aHR, 1.64; 95% CI, 1.31-2.04), and inclusion of individuals regardless of age (n = 10 431; aHR, 1.83; 95% CI, 1.53-2.19).

CONCLUSIONS

Patients with NTS were associated with an increased risk of developing IBD, especially ulcerative colitis.

Impact of liposomal hesperetin in broilers: prospects for improving performance, antioxidant potential, immunity, and resistance against Listeria monocytogenes

Liposomal encapsulated phytogenics, such as liposomal hesperetin, are considered novel substitutes for antibiotics in the broiler industry owing to their improved nutritional and therapeutic properties. Therefore, our key goal was to investigate liposomal hesperetin impact on broiler growth performance, health, antioxidant status, tight junction proteins (TJP), and resistance against Listeria monocytogenes. Four broiler groups were fed 0, 150, 250, or 400 mg/kg of liposomal hesperetin-supplemented diets and experimentally infected with L. monocytogenes strain. Herein, liposomal hesperetin, especially at higher concentrations, augmented broilers FCR with upregulation of genes encoding TJP (occludin, JAM-2, MUC-2), and antioxidant attributes (GPX-1, SOD-1, CAT, HO-1, NQO1, COX2), which reflect enhancing health and welfare of broilers. Muscle antioxidant biomarkers were enhanced; meanwhile, muscle MDA, ROS, and H2O2 levels were reduced in response to 400 mg/kg of liposomal hesperetin. Liposomal hesperetin fortification reduced L. monocytogenes loads and expression levels of its virulence-related genes (flaA, hlyA, and ami). Remarkably, histopathological alterations in intestinal and brain tissues of L. monocytogenes-infected broilers were restored post-inclusion at higher levels of liposomal hesperetin, which reflects increase of the birds' resistance to L. monocytogenes infection. Transcription levels of genes encoding cytokines/chemokines (MyD88, AVBD6, CCL20, IL-1β, IL-18), and autophagy (Bcl-2, LC3, AMPK, AKT, CHOP, Bip, p62, XBP1) were ameliorated following dietary liposomal hesperetin fortification, which suggests enhancement of the birds' immunity and health. Collectively, our research recommends liposomal hesperetin application in broiler diets owing to its promoting impact on growth performance, antioxidant status, immunity, health, and welfare besides its antibacterial, and antivirulence characteristics to fight against L. monocytogenes.

Macrophages orchestrate elimination of Shigella from the intestinal epithelial cell niche via TLR-induced IL-12 and IFN-γ

Bacteria of the genus Shigella replicate in intestinal epithelial cells and cause shigellosis, a severe diarrheal disease that resolves spontaneously in most healthy individuals. During shigellosis, neutrophils are abundantly recruited to the gut, and have long been thought to be central to Shigella control and pathogenesis. However, how shigellosis resolves remains poorly understood due to the longstanding lack of a tractable and physiological animal model. Here, using our newly developed Nlrc4 -/- Casp11 -/- mouse model of shigellosis, we unexpectedly find no major role for neutrophils in limiting Shigella or in disease pathogenesis. Instead, we uncover an essential role for macrophages in the host control of Shigella . Macrophages respond to Shigella via TLRs to produce IL-12, which then induces IFN-γ, a cytokine that is essential to control Shigella replication in intestinal epithelial cells. Collectively, our findings reshape our understanding of the innate immune response to Shigella .

Comparative Analysis of In Vivo and In Vitro Virulence Among Foodborne and Clinical Listeria monocytogenes Strains

Listeria monocytogenes is one of the most important foodborne pathogens that can cause invasive listeriosis. In this study, the virulence levels of 26 strains of L. monocytogenes isolated from food and clinical samples in Shanghai, China, between 2020 and 2022 were analyzed. There were significant differences among isolates in terms of their mortality rate in Galleria mellonella, cytotoxicity to JEG-3 cells, hemolytic activity, and expression of important virulence genes. Compared with other STs, both the ST121 (food source) and ST1930 (clinic source) strains exhibited higher G. mellonella mortality. The 48 h mortality in G. mellonella of lineage II strains was significantly higher than that in lineage I. Compared with other STs, ST1930, ST3, ST5, and ST1032 exhibited higher cytotoxicity to JEG-3 cells. Based on the classification of sources (food and clinical strains) and serogroups (II a, II b, and II c), there were no significant differences observed in terms of G. mellonella mortality, cytotoxicity, and hemolytic activity. In addition, ST121 exhibited significantly higher hly, inlA, inlB, prfA, plcA, and plcB gene expression compared with other STs. A gray relation analysis showed a high correlation between the toxicity of G. mellonella and the expression of the hly and inlB genes; in addition, L. monocytogenes may have a consistent virulence mechanism involving hemolysis activity and cytotoxicity. Through the integration of in vivo and in vitro infection models with information on the expression of virulence factor genes, the differences in virulence between strains or subtypes can be better understood.

Gut microbiota strain richness is species specific and affects engraftment

Despite the fundamental role of bacterial strain variation in gut microbiota function1-6, the number of unique strains of a species that can stably colonize the human intestine is still unknown for almost all species. Here we determine the strain richness (SR) of common gut species using thousands of sequenced bacterial isolates with paired metagenomes. We show that SR varies across species, is transferable by faecal microbiota transplantation, and is uniquely low in the gut compared with soil and lake environments. Active therapeutic administration of supraphysiologic numbers of strains per species increases recipient SR, which then converges back to the population average after dosing is ceased. Stratifying engraftment outcomes by high or low SR shows that SR predicts microbial addition or replacement in faecal transplants. Together, these results indicate that properties of the gut ecosystem govern the number of strains of each species colonizing the gut and thereby influence strain addition and replacement in faecal microbiota transplantation and defined live biotherapeutic products.

Navigating commensal dysbiosis: Gastrointestinal host-pathogen interplay orchestrating opportunistic infections

The gut commensals, which are usually symbiotic or non-harmful bacteria that live in the gastrointestinal tract, have a positive impact on the health of the host. This review, however, specifically discuss distinct conditions where commensals aid in the development of pathogenic opportunistic infections. We discuss that the categorization of gut bacteria as either pathogens or non-pathogens depends on certain circumstances, which are significantly affected by the tissue microenvironment and the dynamic host-microbe interaction. Under favorable circumstances, commensals have the ability to transform into opportunistic pathobionts by undergoing overgrowth. These conditions include changes in the host's physiology, simultaneous infection with other pathogens, effective utilization of nutrients, interactions between different species of bacteria, the formation of protective biofilms, genetic mutations that enhance pathogenicity, acquisition of genes associated with virulence, and the ability to avoid the host's immune response. These processes allow commensals to both initiate infections themselves and aid other pathogens in populating the host. This review highlights the need of having a detailed and sophisticated knowledge of the two-sided nature of gut commensals. Although commensals mostly promote health, they may also become harmful in certain changes in the environment or the body's functioning. This highlights the need of acknowledging the intricate equilibrium in interactions between hosts and microbes, which is crucial for preserving intestinal homeostasis and averting diseases. Finally, we also emphasize the further need of research to better understand and anticipate the behavior of gut commensals in different situations, since they play a crucial and varied role in human health and disease.

Effects of garlic-derived fructan and oligofructose mixtures on intestinal health and constipation relief in mice

BACKGROUND

Garlic polysaccharides (GPs) constitute over 75% of the dry weight of garlic. They are characterized by fructan with a 2,1-β-d-Fruf backbone and 2,6-β-d-Fruf branches. Studies have suggested a role for GPs in regulating gut microbiota but whether they possess a comprehensive function in maintaining intestinal well-being and can serve as effective prebiotics remains unknown. To explore this, varied doses of GPs (1.25-5.0 g kg-1 body weight) and inulin (as a positive control) were administered to Kunming mice via gavage, and their effects on the intestinal epithelial, chemical, and biological barriers were assessed. A constipation model was also established using loperamide to investigate the potential effects of GPs on the relief of constipation.

RESULTS

Administration of GPs significantly upregulated expression of tight-junction proteins and mucins in Kunming mouse small-intestine tissue. Garlic polysaccharides elevated cecal butyric acid content, reduced the abundance of Desulfobacterota, and decreased the ratio of Firmicutes to Bacteroidetes (the F/B ratio). Garlic polysaccharides also promoted the growth of Bacteroides acidifaciens and Clostridium saccharogumia. Tax4Fun functional predictions suggested the potential of GPs to prevent human diseases, reducing the risk of insulin resistance, infectious diseases, and drug resistance. Garlic polysaccharides also exhibited a beneficial effect in alleviating loperamide-induced constipation symptoms by enhancing small intestinal transit, softening stool consistency, accelerating bowel movements, and promoting the release of excitatory neurotransmitters.

CONCLUSIONS

These findings highlight the important role of GPs in maintaining gut fitness by enhancing intestinal barrier function and peristalsis. Garlic polysaccharides are promising prebiotics, potentially contributing to overall intestinal well-being and health. © 2024 Society of Chemical Industry.

Klebsiella oxytoca inhibits Salmonella infection through multiple microbiota-context-dependent mechanisms

The Klebsiella oxytoca species complex is part of the human microbiome, especially during infancy and childhood. K. oxytoca species complex strains can produce enterotoxins, namely, tilimycin and tilivalline, while also contributing to colonization resistance (CR). The relationship between these seemingly contradictory roles is not well understood. Here, by coupling ex vivo assays with CRISPR-mutagenesis and various mouse models, we show that K. oxytoca provides CR against Salmonella Typhimurium. In vitro, the antimicrobial activity against various Salmonella strains depended on tilimycin production and was induced by various simple carbohydrates. In vivo, CR against Salmonella depended on toxin production in germ-free mice, while it was largely toxin-independent in mice with residual microbiota. This was linked to the relative levels of toxin-inducing carbohydrates in vivo. Finally, dulcitol utilization was essential for toxin-independent CR in gnotobiotic mice. Together, this demonstrates that nutrient availability is key to both toxin-dependent and substrate-driven competition between K. oxytoca and Salmonella.

Interference of gastrointestinal barriers with antibiotic susceptibility of foodborne pathogens: an in vitro case study of ciprofloxacin and tetracycline against Salmonella enterica and Listeria monocytogenes

Minimum inhibitory concentrations (MIC) assays are often questioned for their representativeness. Especially when foodborne pathogens are tested, it is of crucial importance to also consider parameters of the human digestive system. Hence, the current study aimed to assess the inhibitory capacity of two antibiotics, ciprofloxacin and tetracycline, against Salmonella enterica and Listeria monocytogenes, under representative environmental conditions. More specifically, aspects of the harsh environment of the human gastrointestinal tract (GIT) were gradually added to the experimental conditions starting from simple aerobic lab conditions into an in vitro simulation of the GIT. In this way, the effects of parameters including the anoxic environment, physicochemical conditions of the GIT (low gastric pH, digestive enzymes, bile acids) and the gut microbiota were evaluated. The latter was simulated by including a representative consortium of selected gut bacteria species. In this study, the MIC of the two antibiotics against the relevant foodborne pathogens were established, under the previously mentioned environmental conditions. The results of S. enterica highlighted the importance of the anaerobic environment when conducting such studies, since the pathogen thrived under such conditions. Inclusion of physicochemical barriers led to exactly opposite results for S. enterica and L. monocytogenes since the former became more susceptible to ciprofloxacin while the latter showed lower susceptibility towards tetracycline. Finally, the inclusion of gut bacteria had a bactericidal effect against L. monocytogenes even in the absence of antibiotics, while gut bacteria protected S. enterica from the effect of ciprofloxacin.

Intestinal colonization resistance in the context of environmental, host, and microbial determinants

Microbial communities that colonize the human gastrointestinal (GI) tract defend against pathogens through a mechanism known as colonization resistance (CR). Advances in technologies such as next-generation sequencing, gnotobiotic mouse models, and bacterial cultivation have enhanced our understanding of the underlying mechanisms and the intricate microbial interactions involved in CR. Rather than being attributed to specific microbial clades, CR is now understood to arise from a dynamic interplay between microbes and the host and is shaped by metabolic, immune, and environmental factors. This evolving perspective underscores the significance of contextual factors, encompassing microbiome composition and host conditions, in determining CR. This review highlights recent research that has shifted its focus toward elucidating how these factors interact to either promote or impede enteric infections. It further discusses future research directions to unravel the complex relationship between host, microbiota, and environmental determinants in safeguarding against GI infections to promote human health.

Intestinal linoleic acid contributes to the protective effects of Akkermansia muciniphila against Listeria monocytogenes infection in mice

Akkermansia muciniphila pretreatment mitigated Listeria monocytogenes infection in mice. A. muciniphila improved gut microbiota disturbed by L. monocytogenes infection and significantly increased the level of intestinal linoleic acid in mice. Linoleic acid strengthened the intestinal epithelial barrier and reduced pathogen translocation partly by regulating NF-κB/MLCK pathway in a GPR40-dependent manner.

Case Report: A case of disseminated cutaneous listeriosis following appendicitis from Lao PDR

Background

Listeria monocytogenes is a food-borne pathogen that is a rare cause of bacteraemia and meningitis in immunosuppressed patients, and carries a high mortality rate. Cutaneous manifestations of listeriosis are rare, and are usually associated with direct inoculation of the skin.

Case

A 41-year-old woman who initially presented to a hospital in Laos with appendicitis was diagnosed with disseminated listeriosis with cutaneous involvement. Intra-abdominal pathology probably contributed to bacterial bloodstream invasion. Initial treatment with meropenem was switched to ampicillin based on best practice, however our patient died 5 days after diagnosis.

Conclusions

This case highlights listeriosis as an important cause of mortality in low- and middle-income countries, exacerbated by poor availability of laboratory diagnostics and ineffective empiric antibiotic regimens. Improvements in food hygiene, surveillance, and increased laboratory capacity are important strategies to reduce rates of infection and clinical outcomes.

Crosstalk between CD8+ T cells and mesenchymal stromal cells in intestine homeostasis and immunity

The intestine represents the most complex cellular network in the whole body. It is constantly faced with multiple types of immunostimulatory agents encompassing from food antigen, gut microbiome, metabolic waste products, and dead cell debris. Within the intestine, most T cells are found in three primary compartments: the organized gut-associated lymphoid tissue, the lamina propria, and the epithelium. The well-orchestrated epithelial-immune-microbial interaction is critically important for the precise immune response. The main role of intestinal mesenchymal stromal cells is to support a structural framework within the gut wall. However, recent evidence from stromal cell studies indicates that they also possess significant immunomodulatory functions, such as maintaining intestinal tolerance via the expression of PDL1/2 and MHC-II molecules, and promoting the development of CD103+ dendritic cells, and IgA+ plasma cells, thereby enhancing intestinal homeostasis. In this review, we will summarize the current understanding of CD8+ T cells and stromal cells alongside the intestinal tract and discuss the reciprocal interactions between T subsets and mesenchymal stromal cell populations. We will focus on how the tissue residency, migration, and function of CD8+ T cells could be potentially regulated by mesenchymal stromal cell populations and explore the molecular mediators, such as TGF-β, IL-33, and MHC-II molecules that might influence these processes. Finally, we discuss the potential pathophysiological impact of such interaction in intestine hemostasis as well as diseases of inflammation, infection, and malignancies.

Gut Microbiota Protects Listeria monocytogenes-Infected Mice by Reducing the Inflammatory Cytokines Storm and Cell Apoptosis

Gut microbiota (GM) has been proven to resist pathogenic infection through nutritional competition, colonization resistance and promotion of the host immune response. However, in clinical practice, GM is mainly used in intestinal diseases, such as Clostridium difficile infection, and there are few reports on its application in the treatment of pathogenic bacterial infections. In this study, GM from healthy mice was transplanted into mice infected with Listeria monocytogenes using fecal microbiota transplantation (FMT) and the effects were observed. We found that GM from healthy mice could reduce the mortality of infected mice and decrease the counts of L. monocytogenes in their liver and spleen. In addition, FMT inhibited the expression of inflammatory factors in the liver and spleen of infected mice. In vitro cell experiments revealed that GM can reduce the count of L. monocytogenes invading Caco-2 cells and inhibit the L. monocytogenes-caused apoptosis. These results indicate that GM can be used to protect mice infected with L. monocytogenes by eliminating the amount of L. monocytogenes in the host and inhibiting the overexpression of inflammatory factors. Hence, this method can potentially replace antibiotics in the treatment of L. monocytogenes infection.

Temporal and spatial dynamics of Listeria monocytogenes central nervous system infection in mice

Listeria monocytogenes is a bacterial pathogen that can cause life-threatening central nervous system (CNS) infections. While mechanisms by which L. monocytogenes and other pathogens traffic to the brain have been studied, a quantitative understanding of the underlying dynamics of colonization and replication within the brain is still lacking. In this study, we used barcoded L. monocytogenes to quantify the bottlenecks and dissemination patterns that lead to cerebral infection. Following intravenous (IV) inoculation, multiple independent invasion events seeded all parts of the CNS from the blood, however, only one clone usually became dominant in the brain. Sequential IV inoculations and intracranial inoculations suggested that clones that had a temporal advantage (i.e., seeded the CNS first), rather than a spatial advantage (i.e., invaded a particular brain region), were the main drivers of clonal dominance. In a foodborne model of cerebral infection with immunocompromised mice, rare invasion events instead led to a highly infected yet monoclonal CNS. This restrictive bottleneck likely arose from pathogen transit into the blood, rather than directly from the blood to the brain. Collectively, our findings provide a detailed quantitative understanding of the L. monocytogenes population dynamics that lead to CNS infection and a framework for studying the dynamics of other cerebral infections.

Assessing microbiome population dynamics using wild-type isogenic standardized hybrid (WISH)-tags

Microbiomes feature recurrent compositional structures under given environmental conditions. However, these patterns may conceal diverse underlying population dynamics that require intrastrain resolution. Here we developed a genomic tagging system, termed wild-type isogenic standardized hybrid (WISH)-tags, that can be combined with quantitative polymerase chain reaction and next-generation sequencing for microbial strain enumeration. We experimentally validated the performance of 62 tags and showed that they can be differentiated with high precision. WISH-tags were introduced into model and non-model bacterial members of the mouse and plant microbiota. Intrastrain priority effects were tested using one species of isogenic barcoded bacteria in the murine gut and the Arabidopsis phyllosphere, both with and without microbiota context. We observed colonization resistance against late-arriving strains of Salmonella Typhimurium in the mouse gut, whereas the phyllosphere accommodated Sphingomonas latecomers in a manner proportional to their presence at the late inoculation timepoint. This demonstrates that WISH-tags are a resource for deciphering population dynamics underlying microbiome assembly across biological systems.

Clostridiales in the Gut Against Listeria monocytogenes Infection Through Growth Inhibition

Listeria monocytogenes (Lm) mainly infect pregnant women, children, the elderly, and other populations with low immunity causing septicemia and meningitis. Healthy people can tolerate higher doses of Lm and only cause gastrointestinal symptoms such as abdominal pain and diarrhea after infection. Compared to the above population, healthy people have a richer and more diverse gut microbiota. In this study, we show that the microbiota in the large intestine and the feces of mice can significantly inhibit the growth of Lm compared to the microbiota in the small intestine. Bacteria larger than 1 μm in the gut microbiota play an important role in inhibiting Lm growth. 16s rRNA sequencing results show that these bacteria are mainly composed of Clostridiales under the phylum Firmicutes, including Ruminiclostridium, Butyricicoccus, Lachnoclostridium, Roseburia, Coprooccus, and Blautia. Thus, we demonstrate that there are some potential functional bacteria in the gut microbiota that can increase resistance against Lm.

Akkermansia muciniphila in infectious disease: A new target for this next-generation probiotic?

The common gastrointestinal commensal Akkermansia muciniphila is a mucin-degrading bacterium that is greatly reduced in individuals consuming a high-fat diet. Increasing evidence from a variety of clinical and pre-clinical studies suggests that oral supplementation with Akkermansia can improve metabolic health and moderate systemic inflammation. We and others have demonstrated a role for Akkermansia administration in protection against infectious disease and the outcome from sepsis. Very recent studies have indicated the molecular mechanisms by which A. muciniphila may interact with the host to influence systemic immune-regulation and control of microbial pathogenesis. Here we consider recent studies which demonstrate the efficacy of this potential next-generation probiotic in animal models of Salmonella Typhimurium, Listeria monocytogenes and Clostridioides difficile as well as influenza virus and phlebovirus. The potential mechanisms by which A. muciniphila may influence local and systemic immune responses are discussed.

Faecal (or intestinal) microbiota transplant: a tool for repairing the gut microbiome

Faecal/intestinal microbiota transplant (FMT/IMT) is an efficacious treatment option for recurrent Clostridioides difficile infection, which has prompted substantial interest in FMT's potential role in the management of a much broader range of diseases associated with the gut microbiome. Despite its promise, the success rates of FMT in these other settings have been variable. This review critically evaluates the current evidence on the impact of clinical, biological, and procedural factors upon the therapeutic efficacy of FMT, and identifies areas that remain nebulous. Due to some of these factors, the optimal therapeutic approach remains unclear; for example, the preferred timing of FMT administration in a heavily antibiotic-exposed hematopoietic cell transplant recipient is not standardized, with arguments that can be made in alternate directions. We explore how these factors may impact upon more informed selection of donors, potential matching of donors to recipients, and aspects of clinical care of FMT recipients. This includes consideration of how gut microbiome composition and functionality may strategically inform donor selection criteria. Furthermore, we review how the most productive advances within the FMT space are those where clinical and translational outcomes are assessed together, and where this model has been used productively in recent years to better understand the contribution of the gut microbiome to human disease, and start the process toward development of more targeted microbiome therapeutics.

Metabolomic signatures of intestinal colonization resistance against Campylobacter jejuni in mice

Introduction

Campylobacter jejuni stands out as one of the leading causes of bacterial enteritis. In contrast to humans, specific pathogen-free (SPF) laboratory mice display strict intestinal colonization resistance (CR) against C. jejuni, orchestrated by the specific murine intestinal microbiota, as shown by fecal microbiota transplantation (FMT) earlier.

Methods

Murine infection models, comprising SPF, SAB, hma, and mma mice were employed. FMT and microbiota depletion were confirmed by culture and culture-independent analyses. Targeted metabolome analyses of fecal samples provided insights into the associated metabolomic signatures.

Results

In comparison to hma mice, the murine intestinal microbiota of mma and SPF mice (with CR against C. jejuni) contained significantly elevated numbers of lactobacilli, and Mouse Intestinal Bacteroides, whereas numbers of enterobacteria, enterococci, and Clostridium coccoides group were reduced. Targeted metabolome analysis revealed that fecal samples from mice with CR contained increased levels of secondary bile acids and fatty acids with known antimicrobial activities, but reduced concentrations of amino acids essential for C. jejuni growth as compared to control animals without CR.

Discussion

The findings highlight the role of microbiota-mediated nutrient competition and antibacterial activities of intestinal metabolites in driving murine CR against C. jejuni. The study underscores the complex dynamics of host-microbiota-pathogen interactions and sets the stage for further investigations into the mechanisms driving CR against enteric infections.

Modelling the effects of antibiotic usage in livestock on human salmonellosis

Antibiotic usage in livestock has been suggested as a driver of antimicrobial resistance in human and livestock populations. This has contributed to the implementation of stewardship programs to curtail usage of antibiotics in livestock. However, the consequences of antibiotic curtailment in livestock on human health are poorly understood. There is the potential for increases in the carriage of pathogens such as Salmonella spp. in livestock, and subsequent increases in human foodborne disease. We use a mathematical model fitted to four case studies, ampicillin and tetracycline usage in fattening pig and broiler poultry populations, to explore the impact of curtailing antibiotic usage in livestock on salmonellosis in humans. Increases in the daily incidence of salmonellosis and a decrease in the proportion of resistant salmonellosis were identified following curtailment of antibiotic usage in livestock. The extent of these increases in human foodborne disease ranged from negligible, to controllable through interventions to target the farm-to-fork pathway. This study provides a motivating example of one plausible scenario following curtailment of antibiotic usage in livestock and suggests that a focus on ensuring good farm-to-fork hygiene and livestock biosecurity is sufficient to mitigate the negative human health consequences of antibiotic stewardship in livestock populations.

The curious case of Prevotella copri

Prevotella copri is an abundant member of the human gastrointestinal microbiome, whose relative abundance has curiously been associated with positive and negative impacts on diseases, such as Parkinson's disease and rheumatoid arthritis. Yet, the verdict is still out on the definitive role of P. copri in human health, and on the effect of different diets on its relative abundance in the gut microbiome. The puzzling discrepancies among P. copri studies have only recently been attributed to the diversity of its strains, which substantially differ in their encoded metabolic patterns from the commonly used reference strain. However, such strain differences cannot be resolved by common 16S rRNA amplicon profiling methods. Here, we scrutinize P. copri, its versatile metabolic potential, and the hypotheses behind the conflicting observations on its association with diet and human health. We also provide suggestions for designing studies and bioinformatics pipelines to better research P. copri.

Listeria monocytogenes infection in pregnant macaques alters the maternal gut microbiome†

OBJECTIVES

The bacterium Listeria monocytogenes (Lm) is associated with adverse pregnancy outcomes. Infection occurs through consumption of contaminated food that is disseminated to the maternal-fetal interface. The influence on the gastrointestinal microbiome during Lm infection remains unexplored in pregnancy. The objective of this study was to determine the impact of listeriosis on the gut microbiota of pregnant macaques.

METHODS

A non-human primate model of listeriosis in pregnancy has been previously described. Both pregnant and non-pregnant cynomolgus macaques were inoculated with Lm and bacteremia and fecal shedding were monitored for 14 days. Non-pregnant animal tissues were collected at necropsy to determine bacterial burden, and fecal samples from both pregnant and non-pregnant animals were evaluated by 16S rRNA next-generation sequencing.

RESULTS

Unlike pregnant macaques, non-pregnant macaques did not exhibit bacteremia, fecal shedding, or tissue colonization by Lm. Dispersion of Lm during pregnancy was associated with a significant decrease in alpha diversity of the host gut microbiome, compared to non-pregnant counterparts. The combined effects of pregnancy and listeriosis were associated with a significant loss in microbial richness, although there were increases in some genera and decreases in others.

CONCLUSIONS

Although pregnancy alone is not associated with gut microbiome disruption, we observed dysbiosis with listeriosis during pregnancy. The macaque model may provide an understanding of the roles that pregnancy and the gut microbiota play in the ability of Lm to establish intestinal infection and disseminate throughout the host, thereby contributing to adverse pregnancy outcomes and risk to the developing fetus.

Phage therapy minimally affects the water microbiota in an Atlantic salmon (Salmo salar) rearing system while still preventing infection

Excessive usage of antibiotics threatens the bacterial diversity in the microbiota of animals. An alternative to antibiotics that has been suggested to not disturb the microbiota is (bacterio)phage therapy. In this study, we challenged germ-free and microbially colonized yolk sac fry of Atlantic salmon with Flavobacterium columnare and observed that the mere presence of a microbiota protected the fish against lethal infection. We then investigated the effect of phage- or oxytetracycline treatment on fish survival and rearing water bacterial community characteristics using 16S rRNA gene amplicon sequencing. Phage treatment led to an increased survival of F. columnare-challenged fish and reduced the relative amounts of the pathogen in the water microbiota. In the absence of F. columnare, phage treatment did not affect the composition or the α-diversity of the rearing water microbiota. In the presence of the phage's host, phage treatment induced minor changes to the bacterial community composition, without affecting the α-diversity. Surprisingly, oxytetracycline treatment had no observable effect on the water microbiota and did not reduce the relative abundance of F. columnare in the water. In conclusion, we showed that phage treatment prevents mortality while not negatively affecting the rearing water microbiota, thus suggesting that phage treatment may be a suitable alternative to antibiotics. We also demonstrated a protective effect of the microbiota in Atlantic salmon yolk sac fry.

The opportunistic nature of gut commensal microbiota

The abundance of gut commensals has historically been associated with health-promoting effects despite the fact that the definition of good or bad microbiota remains condition-specific. The beneficial or pathogenic nature of microbiota is generally dictated by the dimensions of host-microbiota and microbe-microbe interactions. With the increasing popularity of gut microbiota in human health and disease, emerging evidence suggests opportunistic infections promoted by those gut bacteria that are generally considered beneficial. Therefore, the current review deals with the opportunistic nature of the gut commensals and aims to summarise the concepts behind the occasional commensal-to-pathogenic transformation of the gut microbes. Specifically, relevant clinical and experimental studies have been discussed on the overgrowth and bacteraemia caused by commensals. Three key processes and their underlying mechanisms have been summarised to be responsible for the opportunistic nature of commensals, viz. improved colonisation fitness that is dictated by commensal-pathogen interactions and availability of preferred nutrients; pathoadaptive mutations that can trigger the commensal-to-pathogen transformation; and evasion of host immune response as a survival and proliferation strategy of the microbes. Collectively, this review provides an updated concept summary on the underlying mechanisms of disease causative events driven by gut commensal bacteria.

Listeria monocytogenes an Emerging Pathogen: a Comprehensive Overview on Listeriosis, Virulence Determinants, Detection, and Anti-Listerial Interventions

Listeria monocytogenes, the third most deleterious zoonotic pathogen, is a major causative agent of animal and human listeriosis, an infection related to the consumption of contaminated food products. Even though, this pathogen has been responsible for the outbreaks of foodborne infections in the early 1980s, the major outbreaks have been reported during the past two decades. Listeriosis infection in the host is a rare but life-threatening disease with major public health and economic implications. Extensive reports on listeriosis outbreaks are associated with milk and milk products, meat and meat products, and fresh produce. This bacterium can adapt to any environmental and stress conditions, making it a prime causative agent for major foodborne diseases. The pathogen could survive an antibiotic treatment and persist in the host cell, thereby escaping the standard diagnostic practices. The current review strives to provide concise information on the epidemiology, serotypes, and pathogenesis of the L. monocytogenes to decipher the knowledge on the endurance of the pathogen inside the host and food products as a vehicle for Listeria contaminations. In addition, various detection methods for Listeria species from food samples and frontline regimens of L. monocytogenes treatment have also been discussed.

Immunostimulating Commensal Bacteria and Their Potential Use as Therapeutics

The gut microbiome is intimately intertwined with the host immune system, having effects on the systemic immune system. Dysbiosis of the gut microbiome has been linked not only to gastrointestinal disorders but also conditions of the skin, lungs, and brain. Commensal bacteria can affect the immune status of the host through a stimulation of the innate immune system, training of the adaptive immune system, and competitive exclusion of pathogens. Commensal bacteria improve immune response through the production of immunomodulating compounds such as microbe-associated molecular patterns (MAMPs), short-chain fatty acids (SCFAs), and secondary bile acids. The microbiome, especially when in dysbiosis, is plastic and can be manipulated through the introduction of beneficial bacteria or the adjustment of nutrients to stimulate the expansion of beneficial taxa. The complex nature of the gastrointestinal tract (GIT) ecosystem complicates the use of these methods, as similar treatments have various results in individuals with different residential microbiomes and differential health statuses. A more complete understanding of the interaction between commensal species, host genetics, and the host immune system is needed for effective microbiome interventions to be developed and implemented in a clinical setting.

Apolipoprotein E genotype affects innate susceptibility to Listeria monocytogenes infection in aged male mice

Apolipoprotein E (ApoE) is a lipid transport protein that is hypothesized to suppress proinflammatory cytokine production, particularly after stimulation with Toll-like receptor (TLR) ligands such as lipopolysaccharide (LPS). Studies using transgenic ApoE human replacement mice (APOE) expressing one of three different allelic variants suggest that there is a hierarchy in terms of responsiveness to proinflammatory stimuli such as APOE4/E4 > APOE3/E3 > APOE2/E2. In this study, we test the hypothesis that APOE genotype can also predict susceptibility to infection with the facultative intracellular gram-positive bacterium Listeria monocytogenes. We found that bone-marrow-derived macrophages isolated from aged APOE4/E4 mice expressed elevated levels of nitric oxide synthase 2 and were highly resistant to in vitro infection with L. monocytogenes compared to APOE3/E3 and APOE2/E2 mice. However, we did not find statistically significant differences in cytokine or chemokine output from either macrophages or whole splenocytes isolated from APOE2/E2, APOE3/E3, or APOE4/E4 mice following L. monocytogenes infection. In vivo, overall susceptibility to foodborne listeriosis also did not differ by APOE genotype in either young (2 mo old) or aged (15 mo old) C57BL/6 mice. However, we observed a sex-dependent susceptibility to infection in aged APOE2/E2 male mice and a sex-dependent resistance to infection in aged APOE4/E4 male mice that was not present in female mice. Thus, these results suggest that APOE genotype does not play an important role in innate resistance to infection with L. monocytogenes but may be linked to sex-dependent changes that occur during immune senescence.

Fatal neonatal listeriosis following L. monocytogenes horizontal transmission highlights neonatal susceptibility to orally acquired listeriosis

We report a case of fulminant fatal neonatal listeriosis due to horizontal transmission of Listeria monocytogenes (Lm) in a neonatal double room. Genomic analyses reveal a close genetic relationship between clinical isolates, supporting cross-contamination. Oral inoculation experiments in adult and neonatal mice show that neonates are susceptible to a low Lm inoculum and that this susceptibility results from the immaturity of the neonatal gut microbiota. Infected neonates should therefore be isolated for as long as they shed Lm in their feces to avoid horizontal transmission and its dire consequences.

A pilot study of dietary fibres on pathogen growth in an ex vivo colonic model reveals their potential ability to limit vancomycin-resistant Enterococcus expansion

Aim: Dietary fibre is important for shaping gut microbiota. The aim of this pilot study was to investigate the impact of dietary fibres on pathogen performance in the presence of gut microbiota. Methods: In an ex vivo gut model, pooled faecal samples were spiked with a cocktail of representative gastrointestinal pathogens and fermented with yeast β-glucan for 24 hours, after which 16S rRNA amplicon sequencing and short-chain and branched-chain fatty acid (SCFA and BCFA) analyses were performed. In addition, oat β-glucan, arabinoxylan, yeast β-glucan, and galactooligosaccharides were each tested against individual representative pathogens and pathogen growth was assessed via qPCR. Glucose served as a control carbon source. Results: Based on 16S rRNA amplicon sequencing, yeast β-glucan selected for higher proportions of Bacteroides (P = 0.0005, ~6 fold) and Clostridia (P = 0.005, ~3.6 fold) while species of Escherichia/Shigella (P = 0.021, ~2.8 fold) and Lactobacillus (P = 0.007, ~ 15.7-fold) were higher in glucose. Pathogen relative abundance did not differ between glucose and yeast β-glucan. In the absence of pathogens, higher production of BCFAs (P = 0.002) and SCFAs (P = 0.002) fatty acids was observed for fibre group(s). For individual pathogens, yeast β-glucan increased growth of Escherichia coli, Salmonella typhimurium, and Listeria monocytogenes (P < 0.05), arabinoxylan increased S. typhimurium (P < 0.05). Tested fibres decreased vancomycin-resistant Enterococcus faecium (P < 0.05), with yeast β-glucan causing a 1-log reduction (P < 0.01), while galactooligosaccharides decreased L. monocytogenes (P < 0.05). Conclusion: Tested fibres differentially influenced the growth of pathogens, but yeast β-glucan could represent a dietary strategy to help limit vancomycin-resistant enterococci (VRE) expansion in the gut.

Alterations of gut microbiome following gastrointestinal surgical procedures and their potential complications

Intestinal microorganisms play a crucial role in shaping the host immunity and maintaining homeostasis. Nevertheless, alterations in gut bacterial composition may occur and these alterations have been linked with the pathogenesis of several diseases. In surgical practice, studies revealed that the microbiome of patients undergoing surgery changes and several post-operative complications seem to be associated with the gut microbiota composition. In this review, we aim to provide an overview of gut microbiota (GM) in surgical disease. We refer to several studies which describe alterations of GM in patients undergoing different types of surgery, we focus on the impacts of peri-operative interventions on GM and the role of GM in development of post-operative complications, such as anastomotic leak. The review aims to enhance comprehension regarding the correlation between GM and surgical procedures based in the current knowledge. However, preoperative and postoperative synthesis of GM needs to be further examined in future studies, so that GM-targeted measures could be assessed and the different surgery complications could be reduced.

Microbial interactions and the homeostasis of the gut microbiome: the role of Bifidobacterium

The human gut is home to trillions of microorganisms that influence several aspects of our health. This dense microbial community targets almost all dietary polysaccharides and releases multiple metabolites, some of which have physiological effects on the host. A healthy equilibrium between members of the gut microbiota, its microbial diversity, and their metabolites is required for intestinal health, promoting regulatory or anti-inflammatory immune responses. In contrast, the loss of this equilibrium due to antibiotics, low fiber intake, or other conditions results in alterations in gut microbiota composition, a term known as gut dysbiosis. This dysbiosis can be characterized by a reduction in health-associated microorganisms, such as butyrate-producing bacteria, enrichment of a small number of opportunistic pathogens, or a reduction in microbial diversity. Bifidobacterium species are key species in the gut microbiome, serving as primary degraders and contributing to a balanced gut environment in various ways. Colonization resistance is a fundamental property of gut microbiota for the prevention and control of infections. This community competes strongly with foreign microorganisms, such as gastrointestinal pathogens, antibiotic-resistant bacteria, or even probiotics. Resistance to colonization is based on microbial interactions such as metabolic cross-feeding, competition for nutrients, or antimicrobial-based inhibition. These interactions are mediated by metabolites and metabolic pathways, representing the inner workings of the gut microbiota, and play a protective role through colonization resistance. This review presents a rationale for how microbial interactions provide resistance to colonization and gut dysbiosis, highlighting the protective role of Bifidobacterium species.

A genome-wide screen in macrophages identifies PTEN as required for myeloid restriction of Listeria monocytogenes infection

Listeria monocytogenes (Lm) is an intracellular foodborne pathogen which causes the severe disease listeriosis in immunocompromised individuals. Macrophages play a dual role during Lm infection by both promoting dissemination of Lm from the gastrointestinal tract and limiting bacterial growth upon immune activation. Despite the relevance of macrophages to Lm infection, the mechanisms underlying phagocytosis of Lm by macrophages are not well understood. To identify host factors important for Lm infection of macrophages, we performed an unbiased CRISPR/Cas9 screen which revealed pathways that are specific to phagocytosis of Lm and those that are required for internalization of bacteria generally. Specifically, we discovered the tumor suppressor PTEN promotes macrophage phagocytosis of Lm and L. ivanovii, but not other Gram-positive bacteria. Additionally, we found that PTEN enhances phagocytosis of Lm via its lipid phosphatase activity by promoting adherence to macrophages. Using conditional knockout mice lacking Pten in myeloid cells, we show that PTEN-dependent phagocytosis is important for host protection during oral Lm infection. Overall, this study provides a comprehensive identification of macrophage factors involved in regulating Lm uptake and characterizes the function of one factor, PTEN, during Lm infection in vitro and in vivo. Importantly, these results demonstrate a role for opsonin-independent phagocytosis in Lm pathogenesis and suggest that macrophages play a primarily protective role during foodborne listeriosis.

Egress of Listeria monocytogenes from Mesenteric Lymph Nodes Depends on Intracellular Replication and Cell-to-Cell Spread

The mesenteric lymph nodes (MLN) function as a barrier to systemic spread for both commensal and pathogenic bacteria in the gut. Listeria monocytogenes, a facultative intracellular foodborne pathogen, readily overcomes this barrier and spreads into the bloodstream, causing life-threatening systemic infections. We show here that intracellular replication protected L. monocytogenes from clearance by monocytes and neutrophils and promoted colonization of the small intestine-draining MLN (sMLN) but was not required for dissemination to the colon-draining MLN (cMLN). Intestinal tissue had enough free lipoate to support LplA2-dependent extracellular growth of L. monocytogenes, but exogenous lipoate in the MLN was severely limited, and so the bacteria could replicate only inside cells, where they used LplA1 to scavenge lipoate from host peptides. When foodborne infection was manipulated to allow ΔlplA1 L. monocytogenes to colonize the MLN to the same extent as wild-type bacteria, the mutant was still never recovered in the spleen or liver of any animal. We found that intracellular replication in the MLN promoted actin-based motility and cell-to-cell spread of L. monocytogenes and that rapid efficient exit from the MLN was actA dependent. We conclude that intracellular replication of L. monocytogenes in intestinal tissues is not essential and serves primarily to amplify bacterial burdens above a critical threshold needed to efficiently colonize the cMLN. In contrast, intracellular replication in the MLN is absolutely required for further systemic spread and serves primarily to promote ActA-mediated cell-to-cell spread.

[Immunomodulation by nutritional intervention in critically ill patients]

Critically ill patients often suffer from a complex and severe immunological dysfunction. The differentiation and function of human immune cells are fundamentally controlled through metabolic processes. New concepts of immunonutrition therefore try to use enteral and parenteral nutrition to positively impact on the immune function of intensive care unit patients. This review article concisely presents the currently available evidence on the commonly used isolated supplements (anti-oxidative substances, amino acids, essential fatty acids) and difficulties related to their clinical use. The second part presents new and more comprehensive concepts of immunonutrition to influence the intestinal microbiome and to modulate the macronutrient composition. Immunonutrition of critically ill patients bears enormous potential and could become a valuable clinical tool for modulation of the immunometabolism of intensive care unit patients.

Role of Resident Microbial Communities in Biofilm-Related Implant Infections: Recent Insights and Implications

The use of medical implants continues to grow as the population ages. Biofilm-related implant infection is the leading cause of medical implant failure and remains difficult to diagnose and treat. Recent technologies have enhanced our understanding of the composition and complex functions of microbiota occupying various body site niches. In this review, we leverage data from molecular sequencing technologies to explore how silent changes in microbial communities from various sites can influence the development of biofilm-related infections. Specifically, we address biofilm formation and recent insights of the organisms involved in biofilm-related implant infections; how composition of microbiomes from skin, nasopharyngeal, and nearby tissue can impact biofilm-formation, and infection; the role of the gut microbiome in implant-related biofilm formation; and therapeutic strategies to mitigate implant colonization.

Alteration of gut microbiome and metabolome by Clostridium butyricum can repair the intestinal dysbiosis caused by antibiotics in mice

This study evaluated the repair effects of Clostridium butyricum (CBX 2021) on the antibiotic (ABX)-induced intestinal dysbiosis in mice by the multi-omics method. Results showed that ABX eliminated more than 90% of cecal bacteria and also exerted adverse effects on the intestinal structure and overall health in mice after 10 days of the treatment. Of interest, supplementing CBX 2021 in the mice for the next 10 days colonized more butyrate-producing bacteria and accelerated butyrate production compared with the mice by natural recovery. The reconstruction of intestinal microbiota efficiently promoted the improvement of the damaged gut morphology and physical barrier in the mice. In addition, CBX 2021 significantly reduced the content of disease-related metabolites and meanwhile promoted carbohydrate digestion and absorption in mice followed the microbiome alternation. In conclusion, CBX 2021 can repair the intestinal ecology of mice damaged by the antibiotics through reconstructing gut microbiota and optimizing metabolic functions.

Impact of Intensive Care Unit Nutrition on the Microbiome and Patient Outcomes

The bipartite relationship between nutrition and the intestinal microbiome represents an exciting frontier in critical care medicine. In this review, the authors first address these topics independently, leading with a summary of recent clinical studies assessing intensive care unit nutritional strategies, followed by an exploration of the microbiome in the context of perioperative and intensive care, including recent clinical data implicating microbial dysbiosis as a key driver of clinical outcomes. Finally, the authors address the intersection of nutrition and the microbiome, exploring the use of supplemental pre-, pro-, and synbiotics to influence microbial composition and improve outcomes in critically ill and postsurgical patients.

Primary spontaneous listerial peritonitis

A male in his mid-60s with chronic kidney disease, ischemic cardiomyopathy, and nonalcoholic cirrhosis due to congestive hepatopathy presented with fever and abdominal pain for two weeks. He underwent diagnostic paracentesis, which noted an ascitic neutrophil count over 7000/mm³. Gram stain of the ascitic fluid showed Gram-positive cocci. He was diagnosed with spontaneous bacterial peritonitis (SBP) and was started on ceftriaxone. Ascites cultures grew Listeria monocytogenes and antibiotics were changed to ampicillin. He received one week of ampicillin while inpatient and seven weeks of oral amoxicillin, at which point his ascitic neutrophil count was less than 250/mm³. He was continued on suppressive amoxicillin for an additional 14 weeks with no recurrence in over a year after the discontinuation of amoxicillin. Though uncommon, L. monocytogenes should be considered a pathogen causing SBP. Focal listerial infections can be treated with penicillins alone while invasive disease may require the addition of aminoglycosides.

Fecal microbiota transplantation reduces mouse mortality from Listeria monocytogenes infection

Listeria monocytogenes (Lm) is a food bacterium with strong pathogenicity which causes infections via the gastrointestinal tract. Mechanisms by which gut microbiota (GM) resist microbial infections have received little attention. Eight-week-old mice were orally inoculated with wild-type Lm EGD-e and fecal microbiota transplantation (FMT) employed. GM richness and diversity of infected mice changed rapidly within 24h. Firmicutes class decreased and Bacteroidetes, Tenericutes and Ruminococcaceae increased significantly. Coprococcus, Blautia and Eubacterium also increased on the 3rd day post-infection. Moreover, GM transplanted from healthy mice reduced mortality of infected mice by approximately 32%. FMT treatment decreased production of TNFα, IFN-γ, IL-1β and IL-6 relative to PBS treatment. In summary, FMT has potential as a treatment against Lm infection and may be used for bacterial resistance management. Further work is required to elucidate the key GM effector molecules.

Clostridioides difficile infection: traversing host-pathogen interactions in the gut

C. difficile is the primary cause for nosocomial infective diarrhoea. For a successful infection, C. difficile must navigate between resident gut bacteria and the harsh host environment. The perturbation of the intestinal microbiota by broad-spectrum antibiotics alters the composition and the geography of the gut microbiota, deterring colonization resistance, and enabling C. difficile to colonize. This review will discuss how C. difficile interacts with and exploits the microbiota and the host epithelium to infect and persist. We provide an overview of C. difficile virulence factors and their interactions with the gut to aid adhesion, cause epithelial damage and mediate persistence. Finally, we document the host responses to C. difficile, describing the immune cells and host pathways that are associated and triggered during C. difficile infection.

Effects of probiotics on hypertension

Emerging data have suggested that probiotics had good potential in regulating intestinal flora and preventing hypertension. Some studies in human and animal models have demonstrated probiotic intervention could attenuate hypertension, regulate intestinal flora to increase the abundance of beneficial bacteria, and regulate intestinal microbial metabolites such as trimethylamine oxide, short-chain fatty acids, and polyphenols. However, there is still some debate as to whether probiotics exert effective benefits. These recently published reviews did not systematically expound on the heterogeneity between the effect and mechanism of probiotics with different types, doses, and carriers to exert antihypertensive effects, as well as the possible application of probiotics in the prevention and treatment of hypertension in food and clinic. Here we try to systematically review the association between hypertension and intestinal microflora, the effect of probiotics and their metabolites on hypertension, and the recent research progress on the specific mechanism of probiotics on hypertension. In addition, we also summarized the potential application of probiotics in antihypertension. Future challenges include elucidating the functions of metabolites produced by microorganisms and their downstream pathway or molecules, identifying specific strains, not just microbial communities, and developing therapeutic interventions that target hypertension by modulation of gut microbes and metabolites.

MicroRNAs induced by Listeria monocytogenes and their role in cells

Listeria monocytogenes (Lm) causes abortions at high rates and threatens newborns' lives. Also, the elderly and immunocompromised individuals are particularly vulnerable neurologically. The bacterium exerts its pathogenesis intracellularly by manipulating cell organs. It manipulates nucleus elements, microRNAs (miRNAs), in order to increase survival and evade immunity. miRNAs are small non-coding RNAs that degrade gene expression post-transcriptionally. Any alteration to the expression of miRNAs affects various cascades in cells, especially immunity-related responses. Thus, utilizing miRNAs as a novel therapeutic agent not only restricts infection but enhances immunity reactions. This review provides an overview of miRNAs in listeriosis, their role in cells, and their prospects as therapy.

Mouse models for bacterial enteropathogen infections: insights into the role of colonization resistance

Globally, enteropathogenic bacteria are a major cause of morbidity and mortality.1-3 Campylobacter, Salmonella, Shiga-toxin-producing Escherichia coli, and Listeria are among the top five most commonly reported zoonotic pathogens in the European Union.4 However, not all individuals naturally exposed to enteropathogens go on to develop disease. This protection is attributable to colonization resistance (CR) conferred by the gut microbiota, as well as an array of physical, chemical, and immunological barriers that limit infection. Despite their importance for human health, a detailed understanding of gastrointestinal barriers to infection is lacking, and further research is required to investigate the mechanisms that underpin inter-individual differences in resistance to gastrointestinal infection. Here, we discuss the current mouse models available to study infections by non-typhoidal Salmonella strains, Citrobacter rodentium (as a model for enteropathogenic and enterohemorrhagic E. coli), Listeria monocytogenes, and Campylobacter jejuni. Clostridioides difficile is included as another important cause of enteric disease in which resistance is dependent upon CR. We outline which parameters of human infection are recapitulated in these mouse models, including the impact of CR, disease pathology, disease progression, and mucosal immune response. This will showcase common virulence strategies, highlight mechanistic differences, and help researchers from microbiology, infectiology, microbiome research, and mucosal immunology to select the optimal mouse model.