The Host Microbiota Contributes to Early Protection Against Lung Colonization by Mycobacterium tuberculosis

Perspectives on Microbiome Therapeutics in Infectious Diseases: A Comprehensive Approach Beyond Immunology and Microbiology

Although global life expectancy has increased over the past 20 years due to advancements in managing infectious diseases, one-fifth of people still die from infections. In response to this ongoing threat, significant efforts are underway to develop vaccines and antimicrobial agents. However, pathogens evolve resistance mechanisms, complicating their control. The COVID-19 pandemic has underscored the limitations of focusing solely on the pathogen-killing strategies of immunology and microbiology to address complex, multisystemic infectious diseases. This highlights the urgent need for practical advancements, such as microbiome therapeutics, that address these limitations while complementing traditional approaches. Our review emphasizes key outcomes in the field, including evidence of probiotics reducing disease severity and insights into host-microbiome crosstalk that have informed novel therapeutic strategies. These findings underscore the potential of microbiome-based interventions to promote physiological function alongside existing strategies aimed at enhancing host immune responses and pathogen destruction. This narrative review explores microbiome therapeutics as next-generation treatments for infectious diseases, focusing on the application of probiotics and their role in host-microbiome interactions. While offering a novel perspective grounded in a cooperative defense system, this review also addresses the practical challenges and limitations in translating these advancements into clinical settings.

Assessment of lower respiratory tract microbiota associated with pulmonary tuberculosis in children

BACKGROUND

The respiratory microbiota plays a crucial role in the development of tuberculosis (TB). While existing research has underscored imbalances in the respiratory microbiota of adult patients with TB, information regarding the lower respiratory tract (LRT) microbiota in pediatric patients with TB remains scarce.

METHODS

We employed 16S rRNA gene sequencing technology to investigate the LRT microbial communities of 85 children of different ages with active TB of different severities, 33 children with infectious diseases other than TB, and 48 sex- and age-matched healthy children.

RESULTS

A marked imbalance in the respiratory microbiota was observed in children with TB, highlighted by reduced alpha diversity and a distinct microbial community structure. Comparative analysis indicated that patients with severe TB exhibited lower Neisseria levels than those with non-severe TB (1.01% vs. 3.93%, respectively; p = .02). Streptococcus and Gemella levels were lower in bacteriologically confirmed TB cases compared with clinically diagnosed cases, and higher in healthy children younger than 10 years old than in the older group. Spearman correlation analysis demonstrated significant associations between the microbiota of the LRT and cytokine concentrations in the sputum of children with TB (e.g., an inverse correlation between Veillonella and interleukin-17A).

CONCLUSIONS

TB induced significant dysbiosis in the LRT microbiota of children that was associated with disease severity and the immunological response in the respiratory tract. Our findings may offer a deeper understanding of the role of the respiratory microbiome in TB pathogenesis and progression.

Gut microbiota: a crucial player in the combat against tuberculosis

The mammalian gastrointestinal tract quickly becomes densely populated with foreign microorganisms shortly after birth, thereby establishing a lifelong presence of a microbial community. These commensal gut microbiota serve various functions, such as providing nutrients, processing ingested compounds, maintaining gut homeostasis, and shaping the intestinal structure in the host. Dysbiosis, which is characterized by an imbalance in the microbial community, is closely linked to numerous human ailments and has recently emerged as a key factor in health prognosis. Tuberculosis (TB), a highly contagious and potentially fatal disease, presents a pressing need for improved methods of prevention, diagnosis, and treatment strategies. Thus, we aim to explore the latest developments on how the host's immune defenses, inflammatory responses, metabolic pathways, and nutritional status collectively impact the host's susceptibility to or resilience against Mycobacterium tuberculosis infection. The review addresses how the fluctuations in the gut microbiota not only affect the equilibrium of these physiological processes but also indirectly influence the host's capacity to resist M. tuberculosis. This work highlights the central role of the gut microbiota in the host-microbe interactions and provides novel insights for the advancement of preventative and therapeutic approaches against tuberculosis.

Identification of ferroptosis-related gene signature for tuberculosis diagnosis and therapy efficacy

Diagnosis of tuberculosis remains a challenge when microbiological tests are negative. Immune cell atlas of patients with tuberculosis and healthy controls were established by single-cell transcriptome. Through integrated analysis of scRNA-seq with microarray and bulk RNA sequencing data, a ferroptosis-related gene signature containing ACSL4, CTSB, and TLR4 genes that were associated with tuberculosis disease was identified. Four gene expression datasets from blood samples of patients with tuberculosis, latent tuberculosis infection, and healthy controls were used to assess the diagnostic value of the gene signature. The areas under the ROC curve for the combined gene signature were 1.000, 0.866, 0.912, and 0.786, respectively, in differentiating active tuberculosis from latent infection. During anti-tuberculosis treatment, the expression of the gene signature decreased significantly in cured patients with tuberculosis. In conclusion, the ferroptosis-related gene signature was associated with tuberculosis treatment efficacy and was a promising biomarker for differentiating active tuberculosis from latent infection.

Advances in understanding immune homeostasis in latent tuberculosis infection

Nearly one-fourth of the global population is infected by Mycobacterium tuberculosis (Mtb), and approximately 90%-95% remain asymptomatic as latent tuberculosis infection (LTBI), an estimated 5%-10% of those with latent infections will eventually progress to active tuberculosis (ATB). Although it is widely accepted that LTBI transitioning to ATB results from a disruption of host immune balance and a weakening of protective immune responses, the exact underlying immunological mechanisms that promote this conversion are not well characterized. Thus, it is difficult to accurately predict tuberculosis (TB) progression in advance, leaving the LTBI population as a significant threat to TB prevention and control. This article systematically explores three aspects related to the immunoregulatory mechanisms and translational research about LTBI: (1) the distinct immunocytological characteristics of LTBI and ATB, (2) LTBI diagnostic markers discovery related to host anti-TB immunity and metabolic pathways, and (3) vaccine development focus on LTBI. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology Infectious Diseases > Genetics/Genomics/Epigenetics Immune System Diseases > Genetics/Genomics/Epigenetics.

Synthesis of narrow-spectrum anti-mycobacterial molecules without effect on the diversity of gut microbiota in mice based on the structure of rifampicin

Rifampicin (RIF) is a broad-spectrum antimicrobial agent that is also a first-line drug for treating tuberculosis (TB). Based on the naphthyl ring structure of RIF this study synthesized 16 narrow-spectrum antimicrobial molecules that were specifically anti-Mycobacterium tuberculosis (Mtb). The most potent candidate was 2-((6-hydroxynaphthalen-2-yl) methylene) hydrazine-1-carbothioamide (compound 3c) with minimum inhibitory concentration (MIC) of 1 μg/mL against Mtb. Synergistic anti-Mtb test indicated that none of the combinations of 3c with the major anti-TB drugs are antagonistic. Consistent with RIF, compound 3c induced large amounts of reactive oxygen radicals (ROS) in the cells of Mtb. The killing kinetics of compound 3c and RIF are very similar. Furthermore, molecular docking showed that compound 3c was able to access the RIF binding pocket of the β subunit of Mtb RNA polymerase (RNAP). Experiments in mice showed that compound 3c increased the variety of intestinal flora in mice, while RIF significantly decreased the diversity of intestinal flora in mice. In addition, compound 3c is non-toxic to animal cells with a selection index (SI) much more than 10. The evidence from this study suggests that the further development of 3c could contribute to the development of novel drug for TB treatment.

Microbiota and Immunity during Respiratory Infections: Lung and Gut Affair

Bacterial and viral respiratory tract infections are the most common infectious diseases, leading to worldwide morbidity and mortality. In the past 10 years, the importance of lung microbiota emerged in the context of pulmonary diseases, although the mechanisms by which it impacts the intestinal environment have not yet been fully identified. On the contrary, gut microbial dysbiosis is associated with disease etiology or/and development in the lung. In this review, we present an overview of the lung microbiome modifications occurring during respiratory infections, namely, reduced community diversity and increased microbial burden, and of the downstream consequences on host-pathogen interaction, inflammatory signals, and cytokines production, in turn affecting the disease progression and outcome. Particularly, we focus on the role of the gut-lung bidirectional communication in shaping inflammation and immunity in this context, resuming both animal and human studies. Moreover, we discuss the challenges and possibilities related to novel microbial-based (probiotics and dietary supplementation) and microbial-targeted therapies (antibacterial monoclonal antibodies and bacteriophages), aimed to remodel the composition of resident microbial communities and restore health. Finally, we propose an outlook of some relevant questions in the field to be answered with future research, which may have translational relevance for the prevention and control of respiratory infections.

Bifidobacteria in disease: from head to toe

Bifidobacteria as a strictly anaerobic gram-positive bacteria, is widely distributed in the intestine, vagina and oral cavity, and is one of the first gut flora to colonize the early stages of life. Intestinal flora is closely related to health, and dysbiosis of intestinal flora, especially Bifidobacteria, has been found in a variety of diseases. Numerous studies have shown that in addition to maintaining intestinal homeostasis, Bifidobacteria may be involved in diseases covering all parts of the body, including the nervous system, respiratory system, genitourinary system and so on. This review collects evidence for the variation of Bifidobacteria in typical diseases among various systems, provides mild and effective therapeutic options for those diseases that are difficult to cure, and moves Bifidobacteria from basic research to further clinical applications.

The Interplay between Mycobacterium tuberculosis and Human Microbiome

Tuberculosis (TB), a respiratory disease caused by Mycobacterium tuberculosis (Mtb), is a significant cause of mortality worldwide. The lung, a breeding ground for Mtb, was once thought to be a sterile environment, but has now been found to host its own profile of microbes. These microbes are critical in the development of the host immune system and can produce metabolites that aid in host defense against various pathogens. Mtb infection as well as antibiotics can shift the microbial profile, causing dysbiosis and dampening the host immune response. Additionally, increasing cases of drug resistant TB have impacted the success rates of the traditional therapies of isoniazid, rifampin, pyrazinamide, and ethambutol. Recent years have produced tremendous research into the human microbiome and its role in contributing to or attenuating disease processes. Potential treatments aimed at altering the gut-lung bacterial axis may offer promising results against drug resistant TB and help mitigate the effects of TB.

Causal relationship between gut microbiota and tuberculosis: a bidirectional two-sample Mendelian randomization analysis

BACKGROUND

Growing evidence from observational studies and clinical trials suggests that the gut microbiota is associated with tuberculosis (TB). However, it is unclear whether any causal relationship exists between them and whether causality is bidirectional.

METHODS

A bidirectional two-sample Mendelian randomization (MR) analysis was performed. The genome-wide association study (GWAS) summary statistics of gut microbiota were obtained from the MiBioGen consortium, while the GWAS summary statistics of TB and its specific phenotypes [respiratory tuberculosis (RTB) and extrapulmonary tuberculosis (EPTB)] were retrieved from the UK Biobank and the FinnGen consortium. And 195 bacterial taxa from phylum to genus were analyzed. Inverse variance weighted (IVW), MR-Egger regression, maximum likelihood (ML), weighted median, and weighted mode methods were applied to the MR analysis. The robustness of causal estimation was tested using the heterogeneity test, horizontal pleiotropy test, and leave-one-out method.

RESULTS

In the UK Biobank database, we found that 11 bacterial taxa had potential causal effects on TB. Three bacterial taxa genus.Akkermansia, family.Verrucomicrobiacea, order.Verrucomicrobiales were validated in the FinnGen database. Based on the results in the FinnGen database, the present study found significant differences in the characteristics of gut microbial distribution between RTB and EPTB. Four bacterial taxa genus.LachnospiraceaeUCG010, genus.Parabacteroides, genus.RuminococcaceaeUCG011, and order.Bacillales were common traits in relation to both RTB and TB, among which order.Bacillales showed a protective effect. Additionally, family.Bacteroidacea and genus.Bacteroides were identified as common traits in relation to both EPTB and TB, positively associating with a higher risk of EPTB. In reverse MR analysis, no causal association was identified. No significant heterogeneity of instrumental variables (IVs) or horizontal pleiotropy was found.

CONCLUSION

Our study supports a one-way causal relationship between gut microbiota and TB, with gut microbiota having a causal effect on TB. The identification of characteristic gut microbiota provides scientific insights for the potential application of the gut microbiota as a preventive, diagnostic, and therapeutic tool for TB.

Gut microbiota composition and diversity before, during, and two months after rifamycin-based tuberculosis preventive therapy

Tuberculosis (TB) preventive therapy (TPT) is an effective strategy to eliminate TB in low-incidence settings. Shorter TPT regimens incorporating the antimicrobial class of rifamycins are designed to improve adherence and completion rates but carry the risk of modifications to the gut microbiota. We enrolled six subjects diagnosed with latent TB infection (LTBI) who accepted to initiate TPT. We also enrolled six healthy volunteers unexposed to the rifamycins. We profiled the gut microbiota using 16S rRNA amplicon sequencing (V1-V2 region) to document the immediate effect of rifamycin-based TPT on the gut microbiota composition and tracked recovery to baseline two months after TPT. Overall, TPT accounted for 17% of the variance in gut microbial community dissimilarity. This rifamycin-based TPT induced dysbiosis was characterized by a depletion of butyrate-producing taxa (Clostridium-XIVa and Roseburia) and expansion of potentially pathogenic taxa within the Firmicutes and Proteobacteria phyla. Recovery of the gut microbial composition was incomplete two months after TPT. Robust clinical studies are necessary to comprehensively catalogue TPT-induced gut microbiota dysbiosis to inform strategies to mitigate potential long-term sequelae of this important TB control intervention.

The Causal Impact of the Gut Microbiota on Respiratory Tuberculosis Susceptibility

INTRODUCTION

Recent cross-sectional research has demonstrated a substantial link between tuberculosis (TB) and gut microbiota. Nevertheless, the causal impact of the gut microbiota on TB susceptibility in humans remains unknown.

METHODS

The Mendelian randomization (MR) method was utilized for investigating the causality between them. The main method used for MR analysis was the inverse variance weighted (IVW) test, with the MR-Egger, weighted median, weighted mode, and simple median methods serving as supplements. And several sensitivity tests were carried out to validate the MR findings.

RESULTS

The IVW outcomes suggested that three bacterial traits exhibited associations with susceptibility to respiratory TB after Bonferroni correction, namely Lachnospiraceae UCG010 (odds ratio [OR] 1.73, 95% confidence interval [CI] 1.17-2.55, P = 0.005), Eubacterium (brachy group) (OR 1.33, 95% CI 1.07-1.65, P = 0.009), and Ruminococcaceae UCG005 (OR 0.71, 95% CI 0.52-0.98, P = 0.034). Sensitivity analyses demonstrated that horizontal pleiotropy and heterogeneity were absent, thereby guaranteeing the reliability of the results.

CONCLUSION

This research sheds light on the causal impact of gut microbiota on respiratory tuberculosis susceptibility, improving our knowledge of therapeutic strategies for managing TB.

Alterations in the intestinal microbiota associated with active tuberculosis and latent tuberculosis infection

Objectives

To study the characteristics of intestinal microbiota at different stages of Mycobacterium tuberculosis infection.

Methods

Fecal samples of 19 active tuberculosis (ATB) patients, 21 latent tuberculosis infection (LTBI) individuals, and 20 healthy controls (HC) were collected. Gut microbiota of all the participants were analyzed by 16S rDNA sequencing. Clinical information of ATB patients was also collected and analyzed.

Results

Both ATB and LTBI groups showed significant decreases in microbial diversity and decline of Clostridia. For ATB patients, bacteria within phylum Proteobacteria increased. While for LTBI individuals, genera Prevotella and Rosburia enriched. The abundance of Faecalibacterium, Clostridia and Gammaproteobacteria has the potential to diagnose ATB, with the area under the curve (AUC) of 0.808, 0.784 and 0.717. And Prevotella and Rosburia has the potential to diagnose LTBI, with the AUC of 0.689 and 0.689. Notably, in ATB patients, the relative abundance of Blautia was negatively correlated with the proportions of peripheral T cells and CD8+T cells. And serum direct bilirubin was positively correlated with Bacteroidales, while negatively correlated with Clostridiales in ATB patients.

Conclusions

The specifically changed bacteria are promising markers for ATB and LTBI diagnosis. Some gut bacteria contribute to anti-MTB immunity through interactions with T cells and bilirubin.

Host microbiome in tuberculosis: disease, treatment, and immunity perspectives

Tuberculosis (TB), an airborne pulmonary disease caused by Mycobacterium tuberculosis (M. tb), poses an unprecedented health and economic burden to most of the developing countries. Treatment of TB requires prolonged use of a cocktail of antibiotics, which often manifest several side effects, including stomach upset, nausea, and loss of appetite spurring on treatment non-compliance and the emergence of antibiotic resistant M. tb. The anti-TB treatment regimen causes imbalances in the composition of autochthonous microbiota associated with the human body, which also contributes to major side effects. The microbiota residing in the gastrointestinal tract play an important role in various physiological processes, including resistance against colonization by pathogens, boosting host immunity, and providing key metabolic functions. In TB patients, due to prolonged exposure to anti-tuberculosis drugs, the gut microbiota significantly loses its diversity and several keystone bacterial taxa. This loss may result in a significant reduction in the functional potency of the microbiota, which is a probable reason for poor treatment outcomes. In this review, we discuss the structural and functional changes of the gut microbiota during TB and its treatment. A major focus of the review is oriented to the gut microbial association with micronutrient profiles and immune cell dynamics during TB infection. Furthermore, we summarize the acquisition of anti-microbial resistance in M. tb along with the microbiome-based therapeutics to cure the infections. Understanding the relationship between these components and host susceptibility to TB disease is important to finding potential targets that may be used in TB prevention, progression, and cure.

Exploring the microbiome: Uncovering the link with lung cancer and implications for diagnosis and treatment

Lung cancer is the leading cause of cancer-related deaths worldwide. Tobacco smoking and air pollution are believed to be responsible for more than 90% of lung cancers. Respiratory pathogens are also known to be associated with the initiation and development of lung cancer. Despite the fact that the bacterial biomass in the lungs is lower than that in the intestinal tract, emerging evidence indicates that the lung is colonized by a diverse array of microbes. However, there is limited knowledge regarding the role of dysbiosis of the lung microbiota in the progression of lung cancer. In this review, we summarize the current information about the relationship between the microbiome and lung cancer. The objective is to provide an overview of the core composition of the microbiota in lung cancer as well as the role of specific dysbiosis of the lung microbiota in the progression of lung cancer and treatment of the disease.

The emerging paradigm of Unconventional T cells as a novel therapeutic target for celiac disease

Celiac disease (CD) is an organ-specific autoimmune disorder that occurs in genetically predisposed individuals when exposed to exogenous dietary gluten. This exposure to wheat gluten and related proteins from rye and barley triggers an immune response which leads to the development of enteropathy associated with symptoms of bloating, diarrhea, or malabsorption. The sole current treatment is to follow a gluten-free diet for the rest of one's life. Intestinal barriers are enriched with Unconventional T cells such as iNKT, MAIT, and γδ T cells, which lack or express only a limited range of rearranged antigen receptors. Unconventional T cells play a crucial role in regulating mucosal barrier function and microbial colonization. Unconventional T cell populations are widely represented in diseased conditions, where changes in disease activity related to iNKT and MAIT cell reduction, as well as γδ T cell expansion, are demonstrated. In this review, we discuss the role and potential employment of Unconventional T cells as a therapeutic target in the pathophysiology of celiac disease.

Gut Microbiota and Respiratory Infections: Insights from Mendelian Randomization

The role of the gut microbiota in modulating the risk of respiratory infections has garnered increasing attention. However, conventional clinical trials have faced challenges in establishing the precise relationship between the two. In this study, we conducted a Mendelian randomization analysis with single nucleotide polymorphisms employed as instrumental variables to assess the causal links between the gut microbiota and respiratory infections. Two categories of bacteria, family Lactobacillaceae and genus Family XIII AD3011, were causally associated with the occurrence of upper respiratory tract infections (URTIs). Four categories of gut microbiota existed that were causally associated with lower respiratory tract infections (LRTIs), with order Bacillales and genus Paraprevotella showing a positive association and genus Alistipes and genus Ruminococcaceae UCG009 showing a negative association. The metabolites and metabolic pathways only played a role in the development of LRTIs, with the metabolite deoxycholine acting negatively and menaquinol 8 biosynthesis acting positively. The identification of specific bacterial populations, metabolites, and pathways may provide new clues for mechanism research concerning therapeutic interventions for respiratory infections. Future research should focus on elucidating the potential mechanisms regulating the gut microbiota and developing effective strategies to reduce the incidence of respiratory infections. These findings have the potential to significantly improve global respiratory health.

MUC5AC Genetic Variation Is Associated With Tuberculous Meningitis Cerebral Spinal Fluid Cytokine Responses and Mortality

BACKGROUND

The purpose of this study was to assess if single nucleotide polymorphisms (SNPs) in lung mucins MUC5B and MUC5AC are associated with Mycobacterium tuberculosis outcomes.

METHODS

Independent SNPs in MUC5B and MUC5AC (genotyped by Illumina HumanOmniExpress array) were assessed for associations with tumor necrosis factor (TNF) concentrations (measured by immunoassay) in cerebral spinal fluid (CSF) from tuberculous meningitis (TBM) patients. SNPs associated with CSF TNF concentrations were carried forward for analyses of pulmonary and meningeal tuberculosis susceptibility and TBM mortality.

RESULTS

MUC5AC SNP rs28737416 T allele was associated with lower CSF concentrations of TNF (P = 1.8 × 10-8) and IFN-γ (P = 2.3 × 10-6). In an additive genetic model, rs28737416 T/T genotype was associated with higher susceptibility to TBM (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.03-1.49; P = .02), but not pulmonary tuberculosis (OR, 1.11, 95% CI, .98-1.25; P = .10). TBM mortality was higher among participants with the rs28737416 T/T and T/C genotypes (35/119, 30.4%) versus the C/C genotype (11/89, 12.4%; log-rank P = .005) in a Vietnam discovery cohort (n = 210), an independent Vietnam validation cohort (n = 87; 9/87, 19.1% vs 1/20, 2.5%; log-rank P = .02), and an Indonesia validation cohort (n = 468, 127/287, 44.3% vs 65/181, 35.9%; log-rank P = .06).

CONCLUSIONS

MUC5AC variants may contribute to immune changes that influence TBM outcomes.

Impact of the gut-lung axis on tuberculosis susceptibility and progression

Tuberculosis (TB) has remained at the forefront of the global infectious disease burden for centuries. Concerted global efforts to eliminate TB have been hindered by the complexity of Mycobacterium tuberculosis (Mtb), the emergence of antibiotic resistant Mtb strains and the recent impact of the ongoing pandemic of coronavirus disease 2019 (COVID19). Examination of the immunomodulatory role of gastrointestinal microbiota presents a new direction for TB research. The gut microbiome is well-established as a critical modulator of early immune development and inflammatory responses in humans. Recent studies in animal models have further substantiated the existence of the 'gut-lung axis', where distal gastrointestinal commensals modulate lung immune function. This gut microbiome-lung immune crosstalk is postulated to have an important correlation with the pathophysiology of TB. Further evaluation of this gut immunomodulation in TB may provide a novel avenue for the exploration of therapeutic targets. This mini-review assesses the proposed mechanisms by which the gut-lung axis impacts TB susceptibility and progression. It also examines the impact of current anti-TB therapy on the gut microbiome and the effects of gut dysbiosis on treatment outcomes. Finally, it investigates new therapeutic targets, particularly the use of probiotics in treatment of antibiotic resistant TB and informs future developments in the field.

The gut and lung microbiota in pulmonary tuberculosis: susceptibility, function, and new insights into treatment

INTRODUCTION

Tuberculosis (TB) is a chronic infectious disease caused by mycobacterium tuberculosis (Mtb) that poses a major threat to human health.

AREAS COVERED

Herein, we aim to review the alteration of the microbiota in gut and respiratory during TB development, the potential function and mechanisms of microbiota in the pathogenesis of Mtb infection, and the impact of antibiotic treatment on the microbiota. In addition, we discuss the potential new paradigm for the use of microbiota-based treatments such as probiotics and prebiotics in the treatment of TB.

EXPERT OPINION

Studies have shown that trillions of micro-organisms live in the human gut and respiratory tract, acting as gatekeepers in maintaining immune homeostasis and respiratory physiology and playing a beneficial or hostile role in the development of TB. Anti-TB antibiotics may cause microecological imbalances in the gut and respiratory tract, and microbiome-based therapeutics may be a promising strategy for TB treatment. Appropriate probiotics and prebiotics supplementation, along with antimycobacterial treatment, will improve the therapeutic effect of TB treatment and protect the gut and respiratory microbiota from dysbiosis.

Characteristics of the intestinal microflora in children receiving anti-tuberculosis therapy

The progress in investigating microbiome in children and adolescents as well as its impact on maintaining health is considered one of the most significant achievements of modern medicine. In children with various diseases, the qualitative and quantitative indicators of the intestinal microflora change, which causes the development of dysbiosis. The assessing changes in intestinal microflora in children during treatment with anti- tuberculosis drugs has retained its importance and relevance due to insufficient data in the field, which requires a more detailed understanding of this problem. The presented article assesses the state of gut microbial biocenosis in children receiving anti-tuberculosis treatment. The purpose of the study: to study the microbial landscape of the colonic contents in children receiving anti-tuberculosis therapy. Materials and methods. The study included 24 children with verified tuberculosis of the respiratory organs receiving treatment in a 24-hour hospital of the Kuzbass Clinical Phthisiopulmonological Medical Center named after I.F. Kopylova. The study of intestinal microflora was carried out by a quantitative bacteriological method. The material of the study was feces collected in a sterile disposable container, which was delivered to the Department of Microbiology, Immunology and Virology of the Federal State Budgetary Educational Institution of the Russian Ministry of Health. Results. Dysbiosis with predominance of microecological disorders of II (41.7%) and III (37.3%) degrees was detected in all children receiving anti-tuberculosis therapy. The microbial landscape of the intestine was characterized by a decrease in the quantitative content of representatives of the obligate flora Bifidobacterium spp. in 66.7% of children and Lactobacillus spp. in 45.8%, an increase in the number of facultative microorganisms: E. coli lac+ and Citrobacter freundii in 12.5%. Maintaining a full-fledged and active intestinal normobiota is possible by ensuring its dynamic control in children with tuberculosis during treatment. The results of studying the characteristics of the microbiota suggest that patients need probiotic therapy during the treatment of tuberculosis. Conclusion. Microecological disorders in children with tuberculosis therapy were characterized by a decrease in the quantitative content of representatives of obligate flora and an increase in the number of facultative microorganisms. Also in the material, various types of fungi of the genus Candida were identified.

Role of gut microbiota in infectious and inflammatory diseases

Thousands of microorganisms compose the human gut microbiota, fighting pathogens in infectious diseases and inhibiting or inducing inflammation in different immunological contexts. The gut microbiome is a dynamic and complex ecosystem that helps in the proliferation, growth, and differentiation of epithelial and immune cells to maintain intestinal homeostasis. Disorders that cause alteration of this microbiota lead to an imbalance in the host’s immune regulation. Growing evidence supports that the gut microbial community is associated with the development and progression of different infectious and inflammatory diseases. Therefore, understanding the interaction between intestinal microbiota and the modulation of the host’s immune system is fundamental to understanding the mechanisms involved in different pathologies, as well as for the search of new treatments. Here we review the main gut bacteria capable of impacting the immune response in different pathologies and we discuss the mechanisms by which this interaction between the immune system and the microbiota can alter disease outcomes.

Mycobacterium potentiates protection from colorectal cancer by gut microbial alterations

Not only are many Mycobacteria pathogens, but they can act as strong non-specific immunopotentiators, generating beneficial effects on the pathogenesis of some diseases. However, there has been no direct evidence of the effect of mycobacterial species on colorectal cancer (CRC). Herein, we showed that there may be a meaningful inverse correlation between the incidence of tuberculosis and CRC based on global statistics and that heat-killed Mycobacterial tuberculosis and live Mycobacterium bovis (Bacillus Calmette-Guérin strain) could ameliorate CRC development. In particular, using a faecal microbiota transplantation and a comparison between separate housing and cohousing, we demonstrated that the gut microbiota is involved in the protective effects. The microbial alterations can be elucidated by the modulation of antimicrobial activities including those of the Reg3 family genes. Furthermore, interleukin-22 production by T helper cells contributed to the anti-inflammatory activity of Mycobacteria. Our results revealed a novel role of Mycobacteria involving gut microbial alterations in dampening inflammation-associated CRC and an immunological mechanism underlying the interaction between microbes and host immunity.

An Archetypical Model for Engrafting Bacteroides fragilis into Conventional Mice Following Reproducible Antibiotic Conditioning of the Gut Microbiota

Bacteroides fragilis is a commonly investigated commensal bacterium for its protective role in host diseases. Here, we aimed to develop a reproducible antibiotic-based model for conditioning the gut microbiota and engrafting B. fragilis into a conventional murine host. Initially, we selected different combinations of antibiotics, including metronidazole, imipenem, and clindamycin, and investigated their efficacy in depleting the mouse Bacteroides population. We performed 16S rRNA sequencing of DNA isolated from fecal samples at different time points. The α-diversity was similar in mice treated with metronidazole (MET) and differed only at weeks 1 (p = 0.001) and 3 (p = 0.009) during metronidazole/imipenem (MI) treatment. Bacteroides compositions, during the MET and MI exposures, were similar to the pre-antibiotic exposure states. Clindamycin supplementation added to MET or MI regimens eliminated the Bacteroides population. We next repeated metronidazole/clindamycin (MC) treatment in two additional independent experiments, followed by a B. fragilis transplant. MC consistently and reproducibly eliminated the Bacteroides population. The depleted Bacteroides did not recover in a convalescence period of six weeks post-MC treatment. Finally, B. fragilis was enriched for ten days following engraftment into Bacteroides-depleted mice. Our model has potential use in gut microbiota studies that selectively investigate Bacteroides' role in diseases of interest.

Impact of tuberculosis disease on human gut microbiota: a systematic review

INTRODUCTION

This systematic review evaluates the gut microbiota (GM) status in tuberculosis (TB) patients compared to healthy volunteers due to the disease or its treatment.

AREAS COVERED

We conducted a systematic review of all articles published in PubMed, Web of Science, and Embase that assessed the impact of TB disease and anti-tubercular therapy (ATT) on GM from inception till January 2022 (Protocol registration number in PROSPERO: CRD42021261884). Regarding the microbial diversity indices and taxonomy, we found a significant difference in GM status between the TB and healthy control (HC) groups. We found an overabundance of Phylum Proteobacteria and depletion of some short-chain fatty acid-producing bacteria genera like Bifidobacteria, Roseburia, and Ruminococcus in the TB group. We found that ATT exacerbates the degree of dysbiosis caused by Mycobacteria tuberculosis disease.

EXPERT OPINION

The modulation of GM in TB patients in clinical practice may serve as a promising target to reverse the dysbiosis caused. Moreover, this can optimistically change the TB treatment outcome. We expect that appropriate probiotic supplementation with antimycobacterial treatment during tuberculosis disease will help stabilize the GM throughout the treatment phase and protect the GM from dysbiosis.

Effects of second-line anti-tuberculosis drugs on the intestinal microbiota of patients with rifampicin-resistant tuberculosis

Objective

To determine the effects of second-line anti-tuberculosis (TB) drugs on the composition and functions of intestinal microbiota in patients with rifampicin-resistant TB (RR-TB).

Methods

In this cross-sectional study, stool samples and relevant clinical information were collected from patients with RR-TB admitted to the Drug-resistant Specialty Department at Hunan Chest Hospital (Hunan Institute For Tuberculosis Control). The composition and functions of intestinal microbiota were analyzed using metagenomic sequencing and bioinformatics methods.

Results

Altered structural composition of the intestinal microbiota was found when patients from the control, intensive phase treatment, and continuation phase treatment groups were compared (P<0.05). Second-line anti-TB treatment resulted in a decrease in the relative abundance of species, such as Prevotella copri, compared with control treatment. However, the relative abundance of Escherichia coli, Salmonella enterica, and 11 other conditionally pathogenic species increased significantly in the intensive phase treatment group. Based on differential functional analysis, some metabolism-related functions, such as the biosynthesises of phenylalanine, tyrosine, and tryptophan, were significantly inhibited during second-line anti-TB drug treatment, while other functions, such as phenylalanine metabolism, were significantly promoted during the intensive phase of treatment.

Conclusion

Second-line anti-TB drug treatment caused changes in the structural composition of the intestinal microbiota in patients with RR-TB. In particular, this treatment induced a significant increase in the relative abundance of 11 conditionally pathogenic species, including Escherichia coli. Functional analysis revealed significantly decreased biosynthesises of phenylalanine, tyrosine, and tryptophan and significantly increased phenylalanine metabolism.

Bacteriomes in lesions of pulmonary tuberculosis and its association with status of Mycobacterium tuberculosis excretion

BACKGROUND

Bacteria in lung play an important role in sustaining lung health. Understanding the characteristics of bacteriomes in lesions of pulmonary tuberculosis (TB) patients, who excrete Mycobacterium tuberculosis (MTB), is important for TB prevention and effective treatment.  METHODS: In this study, bacteriomes in lesions from TB patients excreting bacteria (TB-E) and those from TB patients not excreting bacteria (TB-NE) with matched normal lung tissues (NT) were compared by 16S rRNA sequencing. Bacterial MetaCyc functions in TB lesions were also predicted by PICRUSt2 tool.

RESULTS

Alpha diversity of bacteria, including Chao 1 and Shannon indexes, for TB-E was significantly higher than those in TB-NE and NT; while for TB-NE group, Chao 1 index was higher than that in NT group. Predominant phyla in TB lesions and NT were Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes, but analysis of similarity (ANOSIM, p < 0.001) revealed significantly different bacterial compositions among TB-E, TB-NE and NT samples. As for bacteriomes in TB lesions, a strong association (ANOSIM, p < 0.001) was observed with the status of MTB excretion. Indicator genera identified in TB-E and TB-NE demonstrated distinctive micro-ecological environments of TB lesions from patients with different clinical manifestations. Co-occurrence analysis revealed a densely-linked bacterial community in TB-NE compared to that in TB-E. MetaCyc functions responsible for menaquinone synthesis and chorismate metabolism that could potentially impact the persistent-state and nutrient metabolism of MTB were enriched in TB-E samples. While in TB-NE samples, enrichment of bacterial MetaCyc function responsible for heme b synthesis might contribute to TB pathology through ferroptosis.

CONCLUSION

Bacteriomes and their MetaCyc functions in TB lesions are elucidated, and they are associated with status of MTB excretion among pulmonary TB patients. These results serve as a basis for designing novel strategies for preventing and treating pulmonary TB disease.

The Relevance of Host Gut Microbiome Signature Alterations on de novo Fatty Acids Synthesis in Patients with Multi-Drug Resistant Tuberculosis

Background

Tuberculosis (TB) is still the single pathogen infectious disease with the largest number of deaths worldwide. The relationship that intestinal microbiota disorder and de novo fatty acid synthesis metabolism have with disease progression in multi-drug resistant TB (MDR-TB) has not yet been fully studied.

Objective

To investigate the effects of long periods of MDR-TB, pre-extensively drug-resistant TB (pre-XDR-TB), or rifampicin-resistant TB (RR-TB) on gut microbiome dysbiosis and advanced disease.

Methods

The sample was chosen between March 2019 and September 2019 in Wenzhou Central Hospital and comprised 11 patients with pre-XDR-TB, 23 patients with RR-TB, and 28 patients with MDR-TB. Healthy individuals were chosen as the control group (CK group). An overnight fast blood sample was drawn via venipuncture into tubes without anticoagulant. For analysis, 300 mg of faeces from patients from the same group was mixed and analysed using DNA extraction, NGS sequencing, and bioinformatics. A QIAamp Fecal DNA Mini Kit was used to isolate the DNA. The extracted DNA was stored at -20°C.

Results

Advanced TB was concurrent with an elevated level of the proportions of acetyl-CoA carboxylase (ACC1) to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and fatty acid synthase (FASN) to GAPDH in de novo fatty acids synthesis, and Eubacterium, Faecalibacterium, Roseburia, and Ruminococcus were increased significantly in RR-TB patients compared to healthy individuals, whereas their abundance in the pre-XDR-TB and MDR-TB groups showed little change in comparison with the control group. Proteobacteria levels were greatly increased in the RR-TB and MDR-TB patient groups but not in the patients with pre-XDR-TB or the healthy subjects. The pre-XDR-TB group exhibited alterations of the intestinal microbiome: coliform flora showed the highest abundance of Verrucomicrobiales, Enterobacteriales, Bifidobacteriales and Lactobacillales. De novo fatty acids synthesis was enhanced in patients and was associated with the gut microbiome dysbiosis induced by the antimicrobials, with Bacteroidetes, Bacteroidales, and Bacteroidaceae displaying the most important correlations on a phylum, order, and family level, respectively.

Conclusion

The progression to advanced TB was observed to be a result of the interaction between multiple interrelated pathways, with gut-lung crosstalk potentially playing a role in patients with drug-resistant TB.

Immunometabolism of Immune Cells in Mucosal Environment Drives Effector Responses against Mycobacterium tuberculosis

Tuberculosis remains a major threat to global public health, with more than 1.5 million deaths recorded in 2020. Improved interventions against tuberculosis are urgently needed, but there are still gaps in our knowledge of the host-pathogen interaction that need to be filled, especially at the site of infection. With a long history of infection in humans, Mycobacterium tuberculosis (Mtb) has evolved to be able to exploit the microenvironment of the infection site to survive and grow. The immune cells are not only reliant on immune signalling to mount an effective response to Mtb invasion but can also be orchestrated by their metabolic state. Cellular metabolism was often overlooked in the past but growing evidence of its importance in the functions of immune cells suggests that it can no longer be ignored. This review aims to gain a better understanding of mucosal immunometabolism of resident effector cells, such as alveolar macrophages and mucosal-associated invariant T cells (MAIT cells), in response to Mtb infection and how Mtb manipulates them for its survival and growth, which could address our knowledge gaps while opening up new questions, and potentially be applied for future vaccination and therapeutic strategies.

Emerging frontiers of antibiotics use and their impacts on the human gut microbiome

Antibiotics, the primary drugs used to cure bacterial diseases, are increasingly becoming ineffective due to the emergence of multiple drug resistance (MDR) leading to recurrence of previously sensitive pathogens. Human gut microbiome (GM), known to play an important role in various physiological processes, consists of pool of diverse microbes. Indiscriminate use of antibiotics during the life span of an individual may lead to development of resistant microbes e.g. Vibrio, Acinetobacter, Escherichia, Klebsiella, Clostridia, etc. in the human GM. Transmission of antibiotic resistant genes (ARGs) between pathogenic and commensal bacteria occurs more frequently in microbiome communities wherein bacteria communicate and exchange cellular constituents both among themselves and with the host. Additionally, co-factors like 'early vs. late' exposure, type of antibiotics and duration of treatment modulate the adverse effects of antibiotics on GM maturation. Furthermore, factors like mode of birth, ethnicity, malnutrition, demography, diet, lifestyle, etc., which influence GM composition, can also indirectly alter the host response to antibiotics. Currently, advanced 'omics' and culturomics approaches are revealing novel avenues to study the interplay between antibiotics and the microbiome and to identify resistant genes in these bacterial communities. Here, we discuss the recent developments that have given insights into the effects of antibiotics on the homeostatic balance of the gut microbiome and thus on human health.

Gut dysbacteriosis attenuates resistance to Mycobacterium bovis infection by decreasing Cyclooxygenase 2 to inhibit endoplasmic reticulum stress

AbstractThe role of gut microbiota has been described as an important influencer of the immune system. Gut-lung axis is critical in the prevention of mycobacterium infection, but the specific mechanism by which dysbiosis affects tuberculosis have not been reported. In this study, we attempted to provide more information on how the gut-lung axis contributes to Mycobacterium bovis (M. bovis) infection. Mice pre-treated with broad-spectrum antibiotics cocktail (Abx) to induce gut dysbiosis. Interestingly, dysbiosis of microbes showed a significant increase in the bacterial burden in lungs, and inhibited the level of COX-2. After fecal transplantation, cyclooxygenase 2（COX-2） expression was restored and the inflammatory lesion in the lung was reduced. Further research found that the deficiency of COX-2 inhibited endoplasmic reticulum stress (ER-stress). This mechanism was completed by COX-2 interaction with BIP. Moreover, we found a positive feedback mechanism by which blocking ER-stress could reduce COX-2 levels via the NF-κB pathway. Taken together, we reveal for the first time gut dysbacteriosis exacerbates M. bovis disease by limiting COX-2 /ER-stress pathway. The finding strengthens the foundation of gut microbiota-targeted therapy for tuberculosis treatment.

Spatial bacterial subpopulations of a human lung lobe and their potential impact on the progression of pulmonary tuberculosis

Better understanding the spatial variation in resident pulmonary bacteria can help to link the disease severity of pulmonary tuberculosis (TB) with lung bacteriomes. This study aimed to investigate bacterial compositions in subniches of a lung lobe from pulmonary TB patient with two separate visible lesions. There were no significant differences between the bacterial compositions in normal tissue and TB lesions, but the bacterial compositions of the two TB lesions differed significantly (P = 0.009). Interestingly, 52 OTUs (relative abundance >1%) that specifically inhabiting certain lung niches were observed and they were affiliated with five phyla. Specific OTUs affiliated with Firmicutes mainly inhabited normal tissues. The dominant phylum in the lung subniches was Proteobacteria, with a relative abundance between 67.03% and 99.99%. Ralstonia, Achromobacter, and Pseudomonas were the most abundant genera, collectively accounting for 34.02% of total bacterial species. A total of 667 of the 700 bacterial connections in a co-correlation network of 145 OTUs (Operational Taxonomic Unit) were positive, indicating a cooperative relationship between bacterial members. Using PICRUSt tool, we do predict bacterial MetaCyc functions responsible for lipid synthesis and heme biosynthesis across the lung lobe that are essential for generation of caseous necrosis and TB disease pathology. MetaCyc pathways responsible for the degradation of aromatic biogenic amines, sulfur oxidation, and denitrification were all related to M.tb growth status, and they were significantly enriched in the lesion with necrosis than that with inflammation. These results open a new insight for us to comprehend the spatial profile of bacteriomes in a pulmonary TB human lung lobe, and shed light on the design of future diagnosis and treatment for pulmonary TB disease.

The Microbiome as Part of the Contemporary View of Tuberculosis Disease

The study of the microbiome has changed our overall perspective on health and disease. Although studies of the lung microbiome have lagged behind those on the gastrointestinal microbiome, there is now evidence that the lung microbiome is a rich, dynamic ecosystem. Tuberculosis is one of the oldest human diseases, it is primarily a respiratory infectious disease caused by strains from the Mycobacterium tuberculosis Complex. Even today, during the COVID-19 pandemic, it remains one of the principal causes of morbidity and mortality worldwide. Tuberculosis disease manifests itself as a dynamic spectrum that ranges from asymptomatic latent infection to life-threatening active disease. The review aims to provide an overview of the microbiome in the tuberculosis setting, both in patients’ and animal models. We discuss the relevance of the microbiome and its dysbiosis, and how, probably through its interaction with the immune system, it is a significant factor in tuberculosis’s susceptibility, establishment, and severity.

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

Despite compartmentalization within the lumen of the gastrointestinal tract, the gut microbiota has a far-reaching influence on immune cell development and function throughout the body. This long-distance relationship is crucial for immune homeostasis, including effective host defense against invading pathogens that cause systemic infections. Herein, we review new insights into how commensal microbes that are spatially restricted to the gut lumen can engage in long-distance relationships with innate and adaptive immune cells at systemic sites to fortify host defenses against infections. In addition, we explore the consequences of intestinal dysbiosis on impaired host defense and immune-mediated pathology during infections, including emerging evidence linking dysbiosis with aberrant systemic inflammation and immune-mediated organ damage in sepsis. As such, therapeutic modification of the gut microbiota is an emerging target for interventions to prevent and/or treat systemic infections and sepsis by harnessing the long-distance relationships between gut microbes and systemic immunity.

Host innate and adaptive immunity shapes the gut microbiota biogeography

The gut microbiota has a fundamental role in the development and the maturation of the host immune system. Both innate and adaptive immune cells have critical functions in microbial pathogen containment and clearance, but the regulation of the commensal microbiome ecosystem in the gastrointestinal tract by these major immune cell populations is incompletely defined. We investigated the role of specific innate and adaptive immune cell in the regulation of the microbiota in the intestinal tract biogeographically. Dendritic cells, macrophages, CD4+ T-cells, CD8+ T-cells, and B-cells were depleted using monoclonal antibodies and clodronate liposomes, and the microbial communities was determined by 16S rRNA gene sequencing. With specific immune cell depletion, distinct microbiota changes were observed. In general, immune cell depleted mice had higher microbiota richness and evenness at all gut anatomical sites. At each gut segment, samples from immune cell-depleted animals clustered away from the Isotype/Liposome control mice. This was especially dramatic for small intestinal microbiota. Specifically, Enterobacteriaceae, Bacteroides acidifaciens and Mucispirillum schaedleri were highly enriched in the mucosa and lumen of the small intestine in immune cell-deficient animals. Further, the mucosal microbiota had higher microbiota evenness compared to luminal microbiota at all gut segments, and the UniFrac distance between B cell depleted and isotype control mice was the largest in duodenum followed by ileum and colon. Taken together, our data suggest that innate and adaptive immune cells specifically contribute to the regulation of the gut microbiota's biogeographical distribution along the gastrointestinal tract, and microbiota in duodenum mucosa are more responsive to host immune changes compared to other anatomical sites. This article is protected by copyright. All rights reserved.

Human gut bacterial metabolism drives Th17 activation and colitis

Bacterial activation of T helper 17 (Th17) cells exacerbates mouse models of autoimmunity, but how human-associated bacteria impact Th17-driven disease remains elusive. We show that human gut Actinobacterium Eggerthella lenta induces intestinal Th17 activation by lifting inhibition of the Th17 transcription factor Rorγt through cell- and antigen-independent mechanisms. E. lenta is enriched in inflammatory bowel disease (IBD) patients and worsens colitis in a Rorc-dependent manner in mice. Th17 activation varies across E. lenta strains, which is attributable to the cardiac glycoside reductase 2 (Cgr2) enzyme. Cgr2 is sufficient to induce interleukin (IL)-17a, a major Th17 cytokine. cgr2+ E. lenta deplete putative steroidal glycosides in pure culture; related compounds are negatively associated with human IBD severity. Finally, leveraging the sensitivity of Cgr2 to dietary arginine, we prevented E. lenta-induced intestinal inflammation in mice. Together, these results support a role for human gut bacterial metabolism in driving Th17-dependent autoimmunity.

Role of the gut microbiota in airway immunity and host defense against respiratory infections

Colonization of the intestine with commensal bacteria is known to play a major role in the maintenance of human health. An altered gut microbiome is associated with various ensuing diseases including respiratory diseases. Here, we summarize current knowledge on the impact of the gut microbiota on airway immunity with a focus on consequences for the host defense against respiratory infections. Specific gut commensal microbiota compositions and functions are depicted that mediate protection against respiratory infections with bacterial and viral pathogens. Lastly, we highlight factors that have imprinting effects on the establishment of the gut microbiota early in life and are potentially relevant in the context of respiratory infections. Deepening our understanding of these relationships will allow to exploit the knowledge on how gut microbiome maturation needs to be modulated to ensure lifelong enhanced resistance towards respiratory infections.

The Role of Gut and Lung Microbiota in Susceptibility to Tuberculosis

Tuberculosis is one of the most common infectious diseases and infectious causes of death worldwide. Over the last decades, significant research effort has been directed towards defining the understanding of the pathogenesis of tuberculosis to improve diagnosis and therapeutic options. Emerging scientific evidence indicates a possible role of the human microbiota in the pathophysiology of tuberculosis, response to therapy, clinical outcomes, and post-treatment outcomes. Although human studies on the role of the microbiota in tuberculosis are limited, published data in recent years, both from experimental and clinical studies, suggest that a better understanding of the gut-lung microbiome axis and microbiome-immune crosstalk could shed light on the specific pathogenetic mechanisms of Mycobacterium tuberculosis infection and identify new therapeutic targets. In this review, we address the current knowledge of the host immune responses against Mycobacterium tuberculosis infection, the emerging evidence on how gut and lung microbiota can modulate susceptibility to tuberculosis, the available studies on the possible use of probiotic-antibiotic combination therapy for the treatment of tuberculosis, and the knowledge gaps and future research priorities in this field.

Differential Diagnosis of Latent Tuberculosis Infection and Active Tuberculosis: A Key to a Successful Tuberculosis Control Strategy

As an ancient infectious disease, tuberculosis (TB) is still the leading cause of death from a single infectious agent worldwide. Latent TB infection (LTBI) has been recognized as the largest source of new TB cases and is one of the biggest obstacles to achieving the aim of the End TB Strategy. The latest data indicate that a considerable percentage of the population with LTBI and the lack of differential diagnosis between LTBI and active TB (aTB) may be potential reasons for the high TB morbidity and mortality in countries with high TB burdens. The tuberculin skin test (TST) has been used to diagnose TB for > 100 years, but it fails to distinguish patients with LTBI from those with aTB and people who have received Bacillus Calmette–Guérin vaccination. To overcome the limitations of TST, several new skin tests and interferon-gamma release assays have been developed, such as the Diaskintest, C-Tb skin test, EC-Test, and T-cell spot of the TB assay, QuantiFERON-TB Gold In-Tube, QuantiFERON-TB Gold-Plus, LIAISON QuantiFERON-TB Gold Plus test, and LIOFeron TB/LTBI. However, these methods cannot distinguish LTBI from aTB. To investigate the reasons why all these methods cannot distinguish LTBI from aTB, we have explained the concept and definition of LTBI and expounded on the immunological mechanism of LTBI in this review. In addition, we have outlined the research status, future directions, and challenges of LTBI differential diagnosis, including novel biomarkers derived from Mycobacterium tuberculosis and hosts, new models and algorithms, omics technologies, and microbiota.

The immunology of sepsis

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to an infection. This recently implemented definition does not capture the heterogeneity or the underlying pathophysiology of the syndrome, which is characterized by concurrent unbalanced hyperinflammation and immune suppression. Here, we review current knowledge of aberrant immune responses during sepsis and recent initiatives to stratify patients with sepsis into subgroups that are more alike from a clinical and/or pathobiological perspective, which could be key for identification of patients who are more likely to benefit from specific immune interventions.

Interrupting the Conversation: Implications for Crosstalk Between Viral and Bacterial Infections in the Asthmatic Airway

Asthma is a heterogeneous, chronic respiratory disease affecting 300 million people and is thought to be driven by different inflammatory endotypes influenced by a myriad of genetic and environmental factors. The complexity of asthma has rendered it challenging to develop preventative and disease modifying therapies and it remains an unmet clinical need. Whilst many factors have been implicated in asthma pathogenesis and exacerbations, evidence indicates a prominent role for respiratory viruses. However, advances in culture-independent detection methods and extensive microbial profiling of the lung, have also demonstrated a role for respiratory bacteria in asthma. In particular, airway colonization by the Proteobacteria species Nontypeable Haemophilus influenzae (NTHi) and Moraxella catarrhalis (Mcat) is associated with increased risk of developing recurrent wheeze and asthma in early life, poor clinical outcomes in established adult asthma and the development of more severe inflammatory phenotypes. Furthermore, emerging evidence indicates that bacterial-viral interactions may influence exacerbation risk and disease severity, highlighting the need to consider the impact chronic airway colonization by respiratory bacteria has on influencing host responses to viral infection. In this review, we first outline the currently understood role of viral and bacterial infections in precipitating asthma exacerbations and discuss the underappreciated potential impact of bacteria-virus crosstalk in modulating host responses. We discuss the mechanisms by which early life infection may predispose to asthma development. Finally, we consider how infection and persistent airway colonization may drive different asthma phenotypes, with a view to identifying pathophysiological mechanisms that may prove tractable to new treatment modalities.

Emerging cellular and molecular interactions between the lung microbiota and lung diseases

With the discovery of the lung microbiota, its study in both pulmonary health and disease has become a vibrant area of emerging research interest. Thus far, most studies have described the lung microbiota composition in lung disease quite well, and some of these studies indicated alterations in lung microbial communities related to the onset and development of lung disease and vice versa. However, the underlying mechanisms, particularly the cellular and molecular links, are still largely unknown. In this review, we highlight the current progress in the complex cellular and molecular mechanisms by which the lung microbiome interacts with immune homeostasis and pulmonary disease pathogenesis to advance our understanding of the elaborate function of the lung microbiota in lung disease. We hope that this work can attract more attention to this still-young yet very promising field to facilitate the identification of new therapeutic targets and provide more innovative therapies. Additional accurate standard-based methodologies and technological breakthroughs are critical to propel the field forward to ultimately achieve the goal of maintaining respiratory health.

THE INTESTINAL COMMENSAL, Bacteroides fragilis, MODULATES HOST RESPONSES TO VIRAL INFECTION AND THERAPY: LESSONS FOR EXPLORATION DURING Mycobacterium tuberculosis INFECTION

The gut microbiota has emerged as a critical player in host health. Bacteroides fragilis is a prominent member of the gut microbiota within the phyla Bacteroidetes. This commensal bacterium produces unique capsular polysaccharides processed by antigen-presenting cells and activates CD4⁺ T cells to secrete inflammatory cytokines. Indeed, due to their immunomodulatory functions, B. fragilis and its capsular polysaccharide-A (PSA) are arguably the most explored single commensal microbiota/symbiotic factor. B. fragilis/PSA has been shown to protect against colitis, encephalomyelitis, colorectal cancer, pulmonary inflammation, and asthma. Here, we review (1) recent data on the immunomodulatory role of B. fragilis/PSA during viral infections and therapy, (2) B. fragilis PSA's dual ability to mediate pro-and anti-inflammatory processes, and the potential for exploring this unique characteristic during intracellular bacterial infections such as with Mycobacterium tuberculosis (3) discuss the protective roles of single commensal-derived probiotic species including B. fragilis in lung inflammation and respiratory infections that may provide essential cues for possible exploration of microbiota based/augmented therapies in tuberculosis (TB). Available data on the relationship between B. fragilis/PSA, the immune system, and disease suggest clinical relevance for developing B. fragilis into a next-generation probiotic or, possibly, the engineering of PSA into a potent carbohydrate-based vaccine.

A Pulmonary Lactobacillus murinus Strain Induces Th17 and RORγt+ Regulatory T Cells and Reduces Lung Inflammation in Tuberculosis

The lungs harbor multiple resident microbial communities, otherwise known as the microbiota. There is an emerging interest in deciphering whether the pulmonary microbiota modulate local immunity, and whether this knowledge could shed light on mechanisms operating in the response to respiratory pathogens. In this study, we investigate the capacity of a pulmonary Lactobacillus strain to modulate the lung T cell compartment and assess its prophylactic potential upon infection with Mycobacterium tuberculosis, the etiological agent of tuberculosis. In naive mice, we report that a Lactobacillus murinus (Lagilactobacillus murinus) strain (CNCM I-5314) increases the presence of lung Th17 cells and of a regulatory T cell (Treg) subset known as RORγt⁺ Tregs. In particular, intranasal but not intragastric administration of CNCM I-5314 increases the expansion of these lung leukocytes, suggesting a local rather than systemic effect. Resident Th17 and RORγt⁺ Tregs display an immunosuppressive phenotype that is accentuated by CNCM I-5314. Despite the well-known ability of M. tuberculosis to modulate lung immunity, the immunomodulatory effect by CNCM I-5314 is dominant, as Th17 and RORγt⁺ Tregs are still highly increased in the lung at 42-d postinfection. Importantly, CNCM I-5314 administration in M. tuberculosis-infected mice results in reduction of pulmonary inflammation, without increasing M. tuberculosis burden. Collectively, our findings provide evidence for an immunomodulatory capacity of CNCM I-5314 at steady state and in a model of chronic inflammation in which it can display a protective role, suggesting that L. murinus strains found in the lung may shape local T cells in mice and, perhaps, in humans.

The role of microbiota in respiratory health and diseases, particularly in tuberculosis

Trillions of beneficial and hostile microorganisms live in the human respiratory and gastrointestinal tracts, which act as gatekeepers in maintaining human health, i.e., protecting the body from pathogens by colonizing mucosal surfaces with microbiota-derived antimicrobial metabolites such as short-chain fatty acids or host-derived cytokines and chemokines. It is widely accepted that the microbiome interacts with each other and with the host in a mutually beneficial relationship. Microbiota in the respiratory tract may also play a crucial role in immune homeostasis, maturation, and maintenance of respiratory physiology. Anti-TB antibiotics may cause dysbiosis in the lung and intestinal microbiota, affecting colonization resistance and making the host more susceptible to Mycobacterium tuberculosis (M. tuberculosis) infection. This review discusses recent advances in our understanding of the lung microbiota composition, the lungs and intestinal microbiota related to respiratory health and diseases, microbiome sequencing and analysis, the bloodstream, and the lymphatic system that underpin the gut-lung axis in M. tuberculosis-infected humans and animals. We also discuss the gut-lung axis interactions with the immune system, the role of the microbiome in TB pathogenesis, and the impact of anti-TB antibiotic therapy on the microbiota in animals, humans, and drug-resistant TB individuals.

The microbiome and rodent models of immune mediated diseases

Over the last six decades production of laboratory rodents have been refined with the aim of eliminating all pathogens, which could influence research results. This has, however, also created rodents with little diversity in their microbiota. Until 10 years ago the impact of the microbiota on the outcome of rodent studies was ignored, but today it is clear that the phenotype of rodent models differs essentially in relation to the environment of origin, i.e. different breeders or different rooms. In this review, we outline the mechanisms behind gut bacterial impact on rodent models of immune mediated diseases, and how differences in environment of origin leads to phenotypic model differences within research areas such as infectious diseases and vaccine development, the metabolic syndrome, gut immunity and inflammation, autoimmunity and allergy. Finally, we sum up some tools to handle this impact to increase reproducibility and translatability of rodent models.

Protective effects of gut microbiota and gut microbiota-derived acetate on chicken colibacillosis induced by avian pathogenic Escherichia coli

Chicken colibacillosis is caused by avian pathogenic Escherichia coli (APEC), and results in huge economic losses to the poultry industry. With the investigation of the gut-lung axis, more studies have demonstrated the important role of gut microbiota in lung inflammation. The precise role of the gut microbiota in chickens-associated colibacillosis, however, is unknown. Thus, this study assessed the function of the gut microbiota in the chicken defense against APEC infection. Chicken gut microbiota was depleted by drinking water with a mixture of antibiotics (Abx), and subsequently, a model of colibacillosis was established by the intranasal perfusion of APEC. The results showed that gut microbiota protects the chicken challenge by APEC from aggravated lung histopathologic injury, up-regulated pro-inflammatory cytokine production, and increased bacterial load in lung tissues compared with controls. In addition, the air-blood barrier permeability was significantly increased in gut microbiota-depleted chickens compared to the control chickens after challenge with APEC. Furthermore, feeding acetate significantly inhibited the lung inflammatory response and the reduced air-blood permeability induced by APEC infection. The expression of free fatty acid receptor 2 (FFAR2), a receptor for acetate, was also increased in the lung after treatment with acetate. In conclusion, depletion of the gut microbiota resulted in increased susceptibility of chickens to APEC challenge, and gut microbiota derived acetate acted as a protective mediator during the APEC challenge. Novel therapeutic targets that focus on the gut microbiota may be effective in controlling colibacillosis in poultry.

Pulmonary and intestinal microbiota dynamics during Gram-negative pneumonia-derived sepsis

Background

The gut microbiome plays a protective role in the host defense against pneumonia. The composition of the lung microbiota has been shown to be predictive of clinical outcome in critically ill patients. However, the dynamics of the lung and gut microbiota composition over time during severe pneumonia remains ill defined. We used a mouse model of pneumonia-derived sepsis caused by Klebsiella pneumoniae in order to follow the pathogen burden as well as the composition of the lung, tongue and fecal microbiota from local infection towards systemic spread.

Results

Already at 6 h post-inoculation with K. pneumoniae, marked changes in the lung microbiota were seen. The alpha diversity of the lung microbiota did not change throughout the infection, whereas the beta diversity did. A shift between the prominent lung microbiota members of Streptococcus and Klebsiella was seen from 12 h onwards and was most pronounced at 18 h post-inoculation (PI) which was also reflected in the release of pro-inflammatory cytokines indicating severe pulmonary inflammation. Around 18 h PI, K. pneumoniae bacteremia was observed together with a systemic inflammatory response. The composition of the tongue microbiota was not affected during infection, even at 18–30 h PI when K. pneumoniae had become the dominant bacterium in the lung. Moreover, we observed differences in the gut microbiota during pulmonary infection. The gut microbiota contributed to the lung microbiota at 12 h PI, however, this decreased at a later stage of the infection.

Conclusions

At 18 h PI, K. pneumoniae was the dominant member in the lung microbiota. The lung microbiota profiles were significantly explained by the lung K. pneumoniae bacterial counts and Klebsiella and Streptococcus were correlating with the measured cytokine levels in the lung and/or blood. The oral microbiota in mice, however, was not influenced by the severity of murine pneumonia, whereas the gut microbiota was affected. This study is of significance for future studies investigating the role of the lung microbiota during pneumonia and sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-021-00398-4.

Obesity-Induced Dysbiosis Exacerbates IFN-γ Production and Pulmonary Inflammation in the Mycobacterium tuberculosis Infection

The microbiota of the gut-lung axis affects local and far-reaching immune responses and might also trigger chronic and inflammatory diseases. We hypothesized that gut dysbiosis induced by obesity, which coexists in countries with a high tuberculosis burden, aggravates the host susceptibility and the pulmonary damage tolerance. To assess our hypothesis, we used a model of high-fat diet (HFD)-induced obesity, followed by infection of C57BL/6 mice with Mycobacterium tuberculosis. We showed that obesity increased the susceptibility, the pulmonary inflammation and IFN-γ levels in M. tuberculosis-infected mice. During the comorbidity obesity and tuberculosis, there is an increase of Bacteroidetes and Firmicutes in the lungs, and an increase of Firmicutes and butyrate in the feces. Depletion of gut microbiota by antibiotic treatment in the obese infected mice reduced the frequencies of CD4+IFN-γ+IL-17- cells and IFN-γ levels in the lungs, associated with an increase of Lactobacillus. Our findings reinforce the role of the gut-lung axis in chronic infections and suggest that the gut microbiota modulation may be a potential host-directed therapy as an adjuvant to treat TB in the context of IFN-γ-mediated immunopathology.