Long-distance relationships - regulation of systemic host defense against infections by the gut microbiota

Recent Insights into the Evolving Role of the Gut Microbiome in Critical Care

This review explores the evolving understanding of gut microbiota's role in critical illness, focusing on how acute illness and exposures in intensive care unit (ICU) environment negatively impact the gut microbiota and the implications of these changes on host responses in critically-ill patients. Focusing on recent findings from clinical and preclinical studies, we discuss the effects of inflammation, enteral nutrient deprivation, and antibiotics on gut microbial dynamics. This review aims to enhance comprehension of microbial dynamics in the ICU and their implications for clinical outcomes and therapeutic strategies.

The Microbiota and Evolution of Obesity

Obesity is a major global concern and is generally attributed to a combination of genetic and environmental factors. Several hypotheses have been proposed to explain the evolutionary origins of obesity epidemic, including thrifty and drifty genotypes, and changes in thermogenesis. Here, we put forward the hypothesis of metaflammation, which proposes that due to intense selection pressures exerted by environmental pathogens, specific genes that help develop a robust defense mechanism against infectious diseases have had evolutionary advantages and that this may contribute to obesity in modern times due to connections between the immune and energy storage systems. Indeed, incorporating the genetic variations of gut microbiota into the complex genetic framework of obesity makes it more polygenic than previously believed. Thus, uncovering the evolutionary origins of obesity requires a multifaceted approach that considers the complexity of human history, the unique genetic makeup of different populations, and the influence of gut microbiome on host genetics.

Zearalenone enhances TSST-1 production by intestinal Staphylococcus and increases uterine immune stress in rats

Zearalenone (ZEA), a mycotoxin prevalent in food crops, poses significant health risks, particularly through its impact on the gut-uterus axis. This study assessed the effects of a 5 mg/kg body weight ZEA dosage in female SD rats, focusing on gut microbiota alterations, inflammatory responses, and uterine changes. Our findings revealed substantial shifts in microbial composition, including significant reductions in beneficial genera such as Akkermansia and Ruminococcaceae and marked increases in pathogenic staphylococci, which correlated with elevated levels of toxic shock syndrome toxin-1 (TSST-1) in serum and uterine tissue. RNA sequencing of uterine samples indicated activation of the extracellular matrix (ECM) pathway, along with significant upregulation of MMP-2 and TIMP-2, enzymes associated with ECM remodelling. Correlation analysis showed a strong link between staphylococcal proliferation and ECM pathway activation, suggesting that ZEA-induced gut dysbiosis contributes to uterine inflammation and structural alterations. These results reveal how ZEA disrupts gut and uterine health, highlighting critical pathways that could serve as targets for future preventive and therapeutic strategies against mycotoxin exposure.

Gut microbiota-derived butyrate improved acute leptospirosis in hamster via promoting macrophage ROS mediated by HDAC3 inhibition

Leptospirosis is a re-emerging worldwide zoonotic disease. Infected patients and animals often exhibit intestinal symptoms. Mounting evidence suggests that host immune responses to bacterial infection are closely associated with intestinal homeostasis. Our previous research has shown that the gut microbiota can protect the host from acute leptospirosis, while the specific bacterial metabolic mediators participating in the pathogenesis remain to be identified. Short-chain fatty acids (SCFAs) are metabolites produced mainly by the gut microbiota that play a role in immune regulation. However, whether SCFAs are the key to protecting the host against leptospirosis and the underlying regulatory mechanisms are unknown. In this study, our results showed that the SCFA butyrate is involved in ameliorating leptospirosis. The depletion of SCFAs by antibiotic cocktail treatment reduced survival time after Leptospira infection while supplementation with butyrate but not acetate or propionate significantly amelioration of leptospirosis. In vitro experiments showed that butyrate treatment enhanced the intracellular bactericidal activity mediated by reactive oxygen species (ROS) production. Mechanistically, butyrate functions as a histone deacetylase 3 inhibitor (HDAC3i) to promote ROS production via monocarboxylate transporter (MCT). The protection of butyrate against acute leptospirosis mediated by ROS was also proven in vivo. Collectively, our data provide evidence that the butyrate-MCT-HDAC3i-ROS signaling axis is a potential therapeutic target for acute leptospirosis. Our work not only interprets the microbial metabolite signaling involved in transkingdom interactions between the host and gut microbiota but also provides a possible target for developing a prevention strategy for acute leptospirosis.

IMPORTANCE

Leptospirosis is a worldwide zoonotic disease caused by Leptospira. An estimated 1 million people are infected with leptospirosis each year. Studies have shown that healthy gut microbiota can protect the host against leptospirosis but the mechanism is not clear. This work elucidated the mechanism of gut microbiota protecting the host against acute leptospirosis. Here, we find that butyrate, a metabolite of gut microbiota, can improve the survival rate of hamsters with leptospirosis by promoting the bactericidal activity of macrophages. Mechanistically, butyrate upregulates reactive oxygen species (ROS) levels after macrophage infection with Leptospira by inhibiting HDAC3. This work confirms the therapeutic potential of butyrate in preventing acute leptospirosis and provides evidence for the benefits of the macrophage-HDAC3i-ROS axis.

Identification of SIBO Subtypes along with Nutritional Status and Diet as Key Elements of SIBO Therapy

Small intestinal bacterial overgrowth (SIBO) is a pathology of the small intestine and may predispose individuals to various nutritional deficiencies. Little is known about whether specific subtypes of SIBO, such as the hydrogen-dominant (H+), methane-dominant (M+), or hydrogen/methane-dominant (H+/M+), impact nutritional status and dietary intake in SIBO patients. The aim of this study was to investigate possible correlations between biochemical parameters, dietary nutrient intake, and distinct SIBO subtypes. This observational study included 67 patients who were newly diagnosed with SIBO. Biochemical parameters and diet were studied utilizing laboratory tests and food records, respectively. The H+/M+ group was associated with low serum vitamin D (p < 0.001), low serum ferritin (p = 0.001) and low fiber intake (p = 0.001). The M+ group was correlated with high serum folic acid (p = 0.002) and low intakes of fiber (p = 0.001) and lactose (p = 0.002). The H+ group was associated with low lactose intake (p = 0.027). These results suggest that the subtype of SIBO may have varying effects on dietary intake, leading to a range of biochemical deficiencies. Conversely, specific dietary patterns may predispose one to the development of a SIBO subtype. The assessment of nutritional status and diet, along with the diagnosis of SIBO subtypes, are believed to be key components of SIBO therapy.

Food, nutrition, and autism: from soil to fork

Food and nutrition-related factors have the potential to impact development of autism spectrum disorder (ASD) and quality of life for people with ASD, but gaps in evidence exist. On 10 November 2022, Tufts University's Friedman School of Nutrition Science and Policy and Food and Nutrition Innovation Institute hosted a 1-d meeting to explore the evidence and evidence gaps regarding the relationships of food and nutrition with ASD. This meeting report summarizes the presentations and deliberations from the meeting. Topics addressed included prenatal and child dietary intake, the microbiome, obesity, food-related environmental exposures, mechanisms and biological processes linking these factors and ASD, food-related social factors, and data sources for future research. Presentations highlighted evidence for protective associations with prenatal folic acid supplementation and ASD development, increases in risk of ASD with maternal gestational obesity, and the potential for exposure to environmental contaminants in foods and food packaging to influence ASD development. The importance of the maternal and child microbiome in ASD development or ASD-related behaviors in the child was reviewed, as was the role of discrimination in leading to disparities in environmental exposures and psychosocial factors that may influence ASD. The role of child diet and high prevalence of food selectivity in children with ASD and its association with adverse outcomes were also discussed. Priority evidence gaps identified by participants include further clarifying ASD development, including biomarkers and key mechanisms; interactions among psychosocial, social, and biological determinants; interventions addressing diet, supplementation, and the microbiome to prevent and improve quality of life for people with ASD; and mechanisms of action of diet-related factors associated with ASD. Participants developed research proposals to address the priority evidence gaps. The workshop findings serve as a foundation for future prioritization of scientific research to address evidence gaps related to food, nutrition, and ASD.

Gut microbial GABAergic signaling improves stress-associated innate immunity to respiratory viral infection

INTRODUCTION

Epidemiological evidences reveal that populations with psychological stress have an increased likelihood of respiratory viral infection involving influenza A virus (IAV) and SARS-CoV-2.

OBJECTIVES

This study aims to explore the potential correlation between psychological stress and increased susceptibility to respiratory viral infections and how this may contribute to a more severe disease progression.

METHODS

A chronic restraint stress (CRS) mouse model was used to infect IAV and estimate lung inflammation. Alveolar macrophages (AMs) were observed in the numbers, function and metabolic-epigenetic properties. To confirm the central importance of the gut microbiome in stress-exacerbated viral pneumonia, mice were conducted through microbiome depletion and gut microbiome transplantation.

RESULTS

Stress exposure induced a decline in Lactobacillaceae abundance and hence γ-aminobutyric acid (GABA) level in mice. Microbial-derived GABA was released in the peripheral and sensed by AMs via GABAAR, leading to enhanced mitochondrial metabolism and α-ketoglutarate (αKG) generation. The metabolic intermediator in turn served as the cofactor for the epigenetic regulator Tet2 to catalyze DNA hydroxymethylation and promoted the PPARγ-centered gene program underpinning survival, self-renewing, and immunoregulation of AMs. Thus, we uncover an unappreciated GABA/Tet2/PPARγ regulatory circuitry initiated by the gut microbiome to instruct distant immune cells through a metabolic-epigenetic program. Accordingly, reconstitution with GABA-producing probiotics, adoptive transferring of GABA-conditioned AMs, or resumption of pulmonary αKG level remarkably improved AMs homeostasis and alleviated severe pneumonia in stressed mice.

CONCLUSION

Together, our study identifies microbiome-derived tonic signaling tuned by psychological stress to imprint resident immune cells and defensive response in the lungs. Further studies are warranted to translate these findings, basically from murine models, into the individuals with psychiatric stress during respiratory viral infection.

The intestinal microbiota modulates the transcriptional landscape of iNKT cells at steady-state and following antigen exposure

Invariant Natural Killer T (iNKT) cells are unconventional T cells that respond to microbe-derived glycolipid antigens. iNKT cells exert fast innate effector functions that regulate immune responses in a variety of contexts, including during infection, cancer, or inflammation. The roles these unconventional T cells play in intestinal inflammation remain poorly defined and vary based on the disease model and species. Our previous work suggested that the gut microbiota influenced iNKT cell functions during dextran sulfate sodium-induced colitis in mice. This study, shows that iNKT cell homeostasis and response following activation are altered in germ-free mice. Using prenatal fecal transplant in specific pathogen-free mice, we show that the transcriptional signatures of iNKT cells at steady state and following αGC-mediated activation in vivo are modulated by the microbiota. Our data suggest that iNKT cells sense the microbiota at homeostasis independently of their T cell receptors. Finally, iNKT cell transcriptional signatures are different in male and female mice. Collectively, our findings suggest that sex and the intestinal microbiota are important factors that regulate iNKT cell homeostasis and responses. A deeper understanding of microbiota-iNKT cell interactions and the impact of sex could improve the development of iNKT cell-based immunotherapies.

Putting Functional Gastrointestinal Disorders within the Spectrum of Inflammatory Disorders Can Improve Classification and Diagnostics of These Disorders

The spectrum, intensity, and overlap of symptoms between functional gastrointestinal disorders (FGIDs) and other gastrointestinal disorders characterize patients with FGIDs, who are incredibly different in their backgrounds. An additional challenge with regard to the diagnosis of FGID and the applicability of a given treatment is the ongoing expansion of the risk factors believed to be connected to these disorders. Many cytokines and inflammatory cells have been found to cause the continuous existence of a low level of inflammation, which is thought to be a basic pathophysiological process. The idea of the gut-brain axis has been created to offer a basic framework for the complex interactions that occur between the nervous system and the intestinal functions, including the involvement of gut bacteria. In this review paper, we intend to promote the hypothesis that FGIDs should be seen through the perspective of the network of the neuroendocrine, immunological, metabolic, and microbiome pathways. This hypothesis arises from an increased understanding of chronic inflammation as a systemic disorder, that is omnipresent in chronic health conditions. A better understanding of inflammation's role in the pathogenesis of FGIDs can be achieved by clustering markers of inflammation with data indicating symptoms, comorbidities, and psycho-social factors. Finding subclasses among related entities of FGIDs may reduce patient heterogeneity and help clarify the pathophysiology of this disease to allow for better treatment.

Pathogenesis and therapeutic opportunities of gut microbiome dysbiosis in critical illness

For many years, it has been hypothesized that pathological changes to the gut microbiome in critical illness is a driver of infections, organ dysfunction, and other adverse outcomes in the intensive care unit (ICU). The advent of contemporary microbiome methodologies and multi-omics tools have allowed researchers to test this hypothesis by dissecting host-microbe interactions in the gut to better define its contribution to critical illness pathogenesis. Observational studies of patients in ICUs have revealed that gut microbial communities are profoundly altered in critical illness, characterized by markedly reduced alpha diversity, loss of commensal taxa, and expansion of potential pathogens. These key features of ICU gut dysbiosis have been associated with adverse outcomes including life-threatening hospital-acquired (nosocomial) infections. Current research strives to define cellular and molecular mechanisms connecting gut dysbiosis with infections and other outcomes, and to identify opportunities for therapeutic modulation of host-microbe interactions. This review synthesizes evidence from studies of critically ill patients that have informed our understanding of intestinal dysbiosis in the ICU, mechanisms linking dysbiosis to infections and other adverse outcomes, as well as clinical trials of microbiota-modifying therapies. Additionally, we discuss novel avenues for precision microbial therapeutics to combat nosocomial infections and other life-threatening complications of critical illness.

Enterococcus faecium HDRsEf1 Promotes Systemic Th1 Responses and Enhances Resistance to SalmonellaTyphimurium Infection

The gut microbiota is known to regulate the immune system and thereby influence susceptibility to infection. In this study, we observed that the administration of Enterococcus faecium HDRsEf1 (HDRsEf1) led to an improvement in the development of the immune system. This was evidenced by an increase in both the spleen index and the area of spleen white pulp. Specifically, the proportion of T helper (Th) 1 cells and the production of IFN-γ and IL-12 were significantly increased in the spleens of mice treated with HDRsEf1. In agreement with the in vivo results, we found that Th1-related cytokines, including IFN-γ and IL-12p70, were strongly induced in splenocytes treated with HDRsEf1. In addition, Th1 cell activation and high-level secretion of IL-12p70 were also confirmed by coculture of CD4+ T cells with bone marrow-derived dendritic cells treated with HDRsEf1. Moreover, the employment of HDRsEf1 was identified to augment resilience against systemic infection provoked by S. Typhimurium and stimulate the expression of the genes for TNFα and iNOS in the initial stage of infection, signifying that reinforced Th1 cells and IL-12 might activate macrophages for antibacterial safeguards. In summary, our study suggests that HDRsEf1 could act as an effective immunobiotic functional agent, promoting systemic Th1 immunological responses and priming defenses against infection.

Secondary bile acids function through the vitamin D receptor in myeloid progenitors to promote myelopoiesis

Metabolic products of the microbiota can alter hematopoiesis. However, the contribution and site of action of bile acids is poorly understood. Here, we demonstrate that the secondary bile acids, deoxycholic acid (DCA) and lithocholic acid (LCA), increase bone marrow myelopoiesis. Treatment of bone marrow cells with DCA and LCA preferentially expanded immunophenotypic and functional colony-forming unit-granulocyte and macrophage (CFU-GM) granulocyte-monocyte progenitors (GMPs). DCA treatment of sorted hematopoietic stem and progenitor cells (HSPCs) increased CFU-GMs, indicating that direct exposure of HSPCs to DCA sufficed to increase GMPs. The vitamin D receptor (VDR) was required for the DCA-induced increase in CFU-GMs and GMPs. Single-cell RNA sequencing revealed that DCA significantly upregulated genes associated with myeloid differentiation and proliferation in GMPs. The action of DCA on HSPCs to expand GMPs in a VDR-dependent manner suggests microbiome-host interactions could directly affect bone marrow hematopoiesis and potentially the severity of infectious and inflammatory disease.

Systemic cytokines inhibition with Imp7 siRNA nanoparticle ameliorates gut injury in a mouse model of ventilator-induced lung injury

Mechanical ventilation (MV) may negatively affect the lungs and cause the release of inflammatory mediators, resulting in extra-pulmonary organ dysfunction. Studies have revealed systemically elevated levels of proinflammatory cytokines in animal models of ventilator-induced lung injury (VILI); however, whether these cytokines have an effect on gut injury and the mechanisms involved remain unknown. In this study, VILI was generated in mice with high tidal volume mechanical ventilation (20 ml/kg). Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 concentrations in serum and gut measured by ELISA showed significant elevation in the VILI mice. Significant increases in gut injury and PANoptosis were observed in the VILI mice, which were positively correlated with the serum levels of TNF-α, IL-1β, and IL-6. The VILI mice displayed intestinal barrier defects, decreased expressions of occludin and zonula occludin-1 (ZO-1), and increased expression of claudin-2 and the activation of myosin light chain (MLC). Importantly, intratracheal administration of Imp7 siRNA nanoparticle effectively inhibited cytokines production and protected mice from VILI-induced gut injury. These data provide evidence of systemic cytokines contributing to gut injury following VILI and highlight the possibility of targeting cytokines inhibition via Imp7 siRNA nanoparticle as a potential therapeutic intervention for alleviating gut injury following VILI.

Conditioning of the immune system by the microbiome

The human intestinal microbiome has coevolved with its host to establish a stable homeostatic relationship with hallmark features of mutualistic symbioses, yet the mechanistic underpinnings of host-microbiome interactions are incompletely understood. Thus, it is an opportune time to conceive a common framework for microbiome-mediated regulation of immune function. We propose the term conditioned immunity to describe the multifaceted mechanisms by which the microbiome modulates immunity. In this regard, microbial colonization is a conditioning exposure that has durable effects on immune function through the action of secondary metabolites, foreign molecular patterns, and antigens. Here, we discuss how spatial niches impact host exposure to microbial products at the level of dose and timing, which elicit diverse conditioned responses.

Docosahexaenoic Acid Promotes Cd Excretion by Restoring the Abundance of Parabacteroides in Cd-Exposed Mice

As a common harmful pollutant, cadmium (Cd) can easily enter the human body through the food chain, posing a major threat to human health. Gut microbiota play a key role in Cd absorption. Docosahexaenoic acid (DHA) is thought to have a potential role in the treatment of Cd poisoning. This study investigated the therapeutic effect and mechanism of DHA in Cd-exposed mice from the perspective of the gut microbiota. The results showed that DHA significantly increased the Cd content in feces and decreased the Cd accumulation in the organs of mice. The gut microbiota results showed that DHA significantly restored the abundance of Parabacteroides in the gut microbiota of Cd-exposed mice. Parabacteroides distasonis (P. distasonis), a representative strain of the Parabacteroides, also showed Cd- and toxicity-reduction capabilities. P. distasonis significantly restored the gut damage caused by Cd exposure. At the same time, P. distasonis reduced the Cd content in the liver, spleen, lung, kidneys, gut, and blood to varying degrees and significantly increased the Cd content in feces. The succinic acid produced by P. distasonis plays an important role in promoting Cd excretion in Cd-exposed mice. Therefore, these results suggest that P. distasonis may have a potential role in DHA-mediated Cd excretion in Cd-exposed mice.

Vascular traffic control of neutrophil recruitment to the liver by microbiota-endothelium crosstalk

During bloodstream infections, neutrophils home to the liver as part of an intravascular immune response to eradicate blood-borne pathogens, but the mechanisms regulating this crucial response are unknown. Using in vivo imaging of neutrophil trafficking in germ-free and gnotobiotic mice, we demonstrate that the intestinal microbiota guides neutrophil homing to the liver in response to infection mediated by the microbial metabolite D-lactate. Commensal-derived D-lactate augments neutrophil adhesion in the liver independent of granulopoiesis in bone marrow or neutrophil maturation and activation in blood. Instead, gut-to-liver D-lactate signaling primes liver endothelial cells to upregulate adhesion molecule expression in response to infection and promote neutrophil adherence. Targeted correction of microbiota D-lactate production in a model of antibiotic-induced dysbiosis restores neutrophil homing to the liver and reduces bacteremia in a model of Staphylococcus aureus infection. These findings reveal long-distance traffic control of neutrophil recruitment to the liver by microbiota-endothelium crosstalk.

Altered gut microbiota composition in children and their caregivers infected with the SARS-CoV-2 Omicron variant

BACKGROUND

Gut microbiota alterations have been implicated in the pathogenesis of coronavirus disease 2019 (COVID-19). This study aimed to explore gut microbiota changes in a prospective cohort of COVID-19 children and their asymptomatic caregivers infected with the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) Omicron variant.

METHODS

A total of 186 participants, including 59 COVID-19 children, 50 asymptomatic adult caregivers, 52 healthy children (HC), and 25 healthy adults (HA), were recruited between 15 April and 31 May 2022. The gut microbiota composition was determined by 16S rRNA gene sequencing in fecal samples collected from the participants. Gut microbiota functional profiling was performed by using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) software.

RESULTS

The gut microbiota analysis of beta diversity revealed that the fecal microbial community of COVID-19 children remained far distantly related to HC. The relative abundances of the phyla Actinobacteria and Firmicutes were decreased, whereas Bacteroidetes, Proteobacteria, and Verrucomicrobiota were increased in COVID-19 children. Feces from COVID-19 children exhibited notably lower abundances of the genera Blautia, Bifidobacterium, Fusicatenibacter, Streptococcus, and Romboutsia and higher abundances of the genera Prevotella, Lachnoclostridium, Escherichia-Shigella, and Bacteroides than those from HC. The enterotype distributions of COVID-19 children were characterized by a high prevalence of enterotype Bacteroides. Similar changes in gut microbiota compositions were observed in asymptomatic caregivers. Furthermore, the microbial metabolic activities of KEGG (Kyoto Encyclopedia of Genes and Genomes) and COG (cluster of orthologous groups of proteins) pathways were perturbed in feces from subjects infected with the SARS-CoV-2 Omicron variant.

CONCLUSION

Our data reveal altered gut microbiota compositions in both COVID-19 children and their asymptomatic caregivers infected with the SARS-CoV-2 Omicron variant, which further implicates the critical role of gut microbiota in COVID-19 pathogenesis.

Necrotizing enterocolitis, gut microbes, and sepsis

Necrotizing enterocolitis (NEC) is a devastating disease in premature infants and the leading cause of death and disability from gastrointestinal disease in this vulnerable population. Although the pathophysiology of NEC remains incompletely understood, current thinking indicates that the disease develops in response to dietary and bacterial factors in the setting of a vulnerable host. As NEC progresses, intestinal perforation can result in serious infection with the development of overwhelming sepsis. In seeking to understand the mechanisms by which bacterial signaling on the intestinal epithelium can lead to NEC, we have shown that the gram-negative bacterial receptor toll-like receptor 4 is a critical regulator of NEC development, a finding that has been confirmed by many other groups. This review article provides recent findings on the interaction of microbial signaling, the immature immune system, intestinal ischemia, and systemic inflammation in the pathogenesis of NEC and the development of sepsis. We will also review promising therapeutic approaches that show efficacy in pre-clinical studies.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

Threonine Facilitates Cd Excretion by Increasing the Abundance of Gut Escherichia coli in Cd-Exposed Mice

Cadmium (Cd) can easily enter the body through the food chain and threaten health since Cd pollution is prevalent in the environment. Gut microbiota is necessary for the reduction of metal ions. To reduce Cd-induced harmful impacts and Cd accumulation in the body, we investigated the effect of amino acids on gut microbiota and Cd excretion in (fecal Cd) Cd-exposed mice. The screening of 20 amino acids showed that threonine (Thr) effectively increased fecal Cd, and reduced Cd-induced intestinal structural damage. The abundance of Escherichia-Shigella genus and KF843036_g significantly increased after the oral administration of Thr. As the type species of the Escherichia-Shigella genus, Escherichia coli exhibited high similarity to KF843036_g species and significantly decreased Cd-induced gut damage. Cd contents in the liver, kidney, and gut of Cd-exposed mice were also significantly (p < 0.05) decreased after E. coli treatment, while the contents in the feces were increased. The results demonstrated the potential roles that gut E. coli might play in Thr-mediated Cd excretion in Cd-exposed mice. The findings may provide important data for better understanding the molecular biological mechanism of Thr in reducing Cd accumulation in the body.