Bacteria pathogens drive host colonic epithelial cell promoter hypermethylation of tumor suppressor genes in colorectal cancer

Crosstalk Between the Gut and Brain: Importance of the Fecal Microbiota in Patient With Brain Tumors

Background

Variations in the gut microbiota may affect the metabolism, inflammation and immune response of the host. Microbiota dysbiosis has been extensively investigated in neurological disorders and diseases of the central nervous system (CNS). However, the alterations of the gut microbiota in patients suffering from brain tumors and the associations of the gut microbiota with these diseases remain unknown. Herein, we investigate the alterations of the gut microbiota community in patients with brain tumors and the associations between the two and further explore microbial markers used for the diagnosis of brain tumors.

Methods

In our study, we recruited 158 participants, consisting of 101 brain tumor patients (65 benign and 36 malignant cases) and 57 age- and sex-matched healthy controls (HCs). We characterized the gut microbial community by using 16S rRNA gene amplicon sequencing and investigated its correlations with clinical features.

Results

The results showed remarkably less microbial ecosystem richness and evenness in patients with brain tumors than in HCs. The gut microbiota community structure underwent profound changes in the brain tumor group, including an increase in the abundances of pathogenic bacteria, such as Fusobacteriota and Proteobacteria and a reduction in the abundances of probiotic bacteria, such as Bifidobacterium or Lachnospira. Moreover, our study indicated more significant correlations and clustering of pathogens in the malignant brain tumor group. Furthermore, a biomarker panel was used to discriminate the brain tumor patients from the healthy controls (AUC: 0.77). Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation revealed an accumulation of harmful metabolites and disorders of the basic physiological pathways in the brain tumor group.

Conclusions

Our study revealed that brain tumor patients may possess divergent host-microbe interactions from those of healthy controls, especially in malignant brain tumor patients. In addition, the intestinal flora may be involved in immune responses and metabolism in the microenvironment of brain tumors. All evidence, including the biomarker panel, suggests that the intestinal flora may be a useful diagnostic and predictive tool and an important preventive target for brain tumors.

Alterations in co-abundant bacteriome in colorectal cancer and its persistence after surgery: a pilot study

There is growing interest in the role of gut microbiome in colorectal cancer (CRC), ranging from screening to disease recurrence. Our study aims to identify microbial markers characteristic of CRC and to examine if changes in bacteriome persist after surgery. Forty-nine fecal samples from 25 non-cancer (NC) individuals and 12 CRC patients, before and 6-months after surgery, were collected for analysis by bacterial 16S rRNA gene sequencing. Bacterial richness and diversity were reduced, while pro-carcinogenic bacteria such as Bacteroides fragilis and Odoribacter splanchnicus were increased in CRC patients compared to NC group. These differences were no longer observed after surgery. Comparison between pre-op and post-op CRC showed increased abundance of probiotic bacteria after surgery. Concomitantly, bacteria associated with CRC progression were observed to have increased after surgery, implying persistent dysbiosis. In addition, functional pathway predictions based on the bacterial 16S rRNA gene data showed that various pathways were differentially enriched in CRC compared to NC. Microbiome signatures characteristic of CRC comprise altered bacterial composition. Elements of these dysbiotic signatures persists even after surgery, suggesting possible field-change in remnant non-diseased colon. Future studies should involve a larger sample size with microbiome data collected at multiple time points after surgery to examine if these dysbiotic patterns truly persist and also correlate with disease outcomes.

MIAOME: Human Microbiome Affect The Host Epigenome

Besides the genetic factors having tremendous influences on the regulations of the epigenome, the microenvironmental factors have recently gained extensive attention for their roles in affecting the host epigenome. There are three major types of microenvironmental factors: microbiota-derived metabolites (MDM), microbiota-derived components (MDC) and microbiota-secreted proteins (MSP). These factors can regulate host physiology by modifying host gene expression through the three highly interconnected epigenetic mechanisms (e.g. histone modifications, DNA modifications, and non-coding RNAs). However, no database was available to provide the comprehensive factors of these types. Herein, a database entitled 'Human Microbiome Affect The Host Epigenome (MIAOME)' was constructed. Based on the types of epigenetic modifications confirmed in the literature review, the MIAOME database captures 1068 (63 genus, 281 species, 707 strains, etc.) human microbes, 91 unique microbiota-derived metabolites & components (16 fatty acids, 10 bile acids, 10 phenolic compounds, 10 vitamins, 9 tryptophan metabolites, etc.) derived from 967 microbes; 50 microbes that secreted 40 proteins; 98 microbes that directly influence the host epigenetic modification, and provides 3 classifications of the epigenome, including (1) 4 types of DNA modifications, (2) 20 histone modifications and (3) 490 ncRNAs regulations, involved in 160 human diseases. All in all, MIAOME has compiled the information on the microenvironmental factors influence host epigenome through the scientific literature and biochemical databases, and allows the collective considerations among the different types of factors. It can be freely assessed without login requirement by all users at: http://miaome.idrblab.net/ttd/

Effects of caloric restriction on the gut microbiome are linked with immune senescence

BACKGROUND

Caloric restriction can delay the development of metabolic diseases ranging from insulin resistance to type 2 diabetes and is linked to both changes in the composition and metabolic function of the gut microbiota and immunological consequences. However, the interaction between dietary intake, the microbiome, and the immune system remains poorly described.

RESULTS

We transplanted the gut microbiota from an obese female before (AdLib) and after (CalRes) an 8-week very-low-calorie diet (800 kcal/day) into germ-free mice. We used 16S rRNA sequencing to evaluate taxa with differential abundance between the AdLib- and CalRes-microbiota recipients and single-cell multidimensional mass cytometry to define immune signatures in murine colon, liver, and spleen. Recipients of the CalRes sample exhibited overall higher alpha diversity and restructuring of the gut microbiota with decreased abundance of several microbial taxa (e.g., Clostridium ramosum, Hungatella hathewayi, Alistipi obesi). Transplantation of CalRes-microbiota into mice decreased their body fat accumulation and improved glucose tolerance compared to AdLib-microbiota recipients. Finally, the CalRes-associated microbiota reduced the levels of intestinal effector memory CD8+ T cells, intestinal memory B cells, and hepatic effector memory CD4+ and CD8+ T cells.

CONCLUSION

Caloric restriction shapes the gut microbiome which can improve metabolic health and may induce a shift towards the naïve T and B cell compartment and, thus, delay immune senescence. Understanding the role of the gut microbiome as mediator of beneficial effects of low calorie diets on inflammation and metabolism may enhance the development of new therapeutic treatment options for metabolic diseases.

TRIAL REGISTRATION

NCT01105143 , "Effects of negative energy balance on muscle mass regulation," registered 16 April 2010. Video Abstract.

Colorectal Cancer Screening in Inflammatory Bowel Diseases-Can Characterization of GI Microbiome Signatures Enhance Neoplasia Detection?

Current noninvasive methods for colorectal cancer (CRC) screening are not optimized for persons with inflammatory bowel diseases (IBDs), requiring patients to undergo frequent interval screening via colonoscopy. Although colonoscopy-based screening reduces CRC incidence in IBD patients, rates of interval CRC remain relatively high, highlighting the need for more targeted approaches. In recent years, the discovery of disease-specific microbiome signatures for both IBD and CRC has begun to emerge, suggesting that stool-based biomarker detection using metagenomics and other culture-independent technologies may be useful for personalized, early, noninvasive CRC screening in IBD patients. Here we discuss the utility of the stool microbiome as a noninvasive CRC screening tool. Comparing the performance of multiple microbiome-based CRC classifiers, including several multi-cohort meta-analyses, we find that noninvasive detection of colorectal adenomas and carcinomas from microbial biomarkers is an active area of study with promising early results.

Novel microbiome signatures for non-invasive diagnosis of adenoma recurrence after colonoscopic polypectomy

BACKGROUND

We previously reported a panel of novel faecal microbiome gene markers for diagnosis of colorectal adenoma and cancer.

AIM

To evaluate whether these markers are useful in detecting adenoma recurrence after polypectomy.

METHODS

Subjects were enrolled in a polyp surveillance study from 2009 to 2019. Stool samples were collected before bowel preparation of index colonoscopy (baseline) and surveillance colonoscopy (follow-up). Fusobacterium nucleatum (Fn), Lachnoclostridium marker (m3), Clostridium hathewayi (Ch) and Bacteroides clarus were quantified in baseline and follow-up samples by quantitative polymerase chain reaction (qPCR) to correlate with adenoma recurrence. Recurrence was defined as new adenomas detected >6 months after polypectomy. Faecal immunochemical test (FIT) was performed for comparison.

RESULTS

A total of 161 baseline and 104 follow-up samples were analysed. Among patients with adenoma recurrence, Fn and m3 increased (both P < 0.05) while Ch were unchanged in follow-up versus baseline samples. Among patients without recurrence, Fn and m3 were unchanged while Ch decreased (P < 0.05) in follow-up versus baseline samples. Logistic regression that included changes of m3, Fn and Ch at follow-up compared with baseline achieved an area under receiver operating characteristic curve (AUROC) of 0.95 (95%CI: 0.84-0.99) with 90.0% sensitivity and 87.0% specificity for detecting recurrent adenoma. Combination of m3, Fn and Ch at follow-up sample achieved AUROC of 0.74 (95%CI: 0.65-0.82) with 81.3% sensitivity and 55.4% specificity for detecting recurrent adenoma. FIT showed limited sensitivity (8.3%) in detecting recurrent adenomas.

CONCLUSION

Our combinations of faecal microbiome gene markers can be potentially useful non-invasive tools for detecting adenoma recurrence.

The role of gut microbiota in patients with benign and malignant brain tumors: a pilot study

Gut microbiota is associated with the growth of various tumors, including malignant gliomas, through the brain-gut axis. Moreover, the gut microbiota in patients with malignant tumors may considerably differ from those with benign tumors. However, the associations of gut microbiota with benign and malignant brain tumors remain unclear. Hence, in order to explore these underlying relationships, patients with benign meningioma (n = 32), malignant glioma (n = 27), and healthy individuals (n = 41) were selected to participate in this study. The results showed that the diversity of the microbial ecosystem in brain tumor patients were less than the healthy controls, while no significant differences were observed between the meningioma and glioma groups. The microbial composition also differed significantly between individuals with brain tumors and healthy participants. In meningioma group, pathogenic bacteria like Enterobacteriaceae were increased, whereas certain carcinogenic bacteria were overrepresented in the glioma group, including Fusobacterium and Akkermansia. Furthermore, benign and malignant brain tumor patients lacked SCFA-producing probiotics. Thus, a microbial biomarker panel including Fusobacterium, Akkermansia, Escherichia/Shigella, Lachnospira, Agathobacter, and Bifidobacterium was established. Diagnostic models confirmed that this panel could distinguish between brain tumor patients and healthy patients. Additionally, gut microbiota can affect the differentiation and proliferation of brain tumors via several metabolic pathways based on annotations from the Kyoto Encyclopedia of Genes and Genomes (KEGG). This is the first study designed to investigate whether gut microbiota differs between benign and malignant brain tumor patients, and our work concluded that intestinal flora is a valuable tool for the diagnosis and treatment of brain tumors.

Albuca Bracteata Polysaccharides Attenuate AOM/DSS Induced Colon Tumorigenesis via Regulating Oxidative Stress, Inflammation and Gut Microbiota in Mice

Inflammation is an important risk factor in the development of inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC). Accumulating evidence indicates that some phytochemicals have anti-cancer properties. Polysaccharides extracted from Albuca bracteata (AB) have been reported to possess anti-neoplastic activities on colorectal cancer (CRC) models. However, it is still unclear whether they exert therapeutic effects on colorectal cancer. In this study, we investigate the properties of polysaccharides of A. bracteate, named ABP. The average molecular weight of ABP was 18.3 kDa and ABP consisted of glucose, mannose, galactose, xylose, galacturonic acid, glucuronic acid at a molar ratio of 37.8:8:2.5:1.7:1:1. An Azoxymethane/Dextran sodium sulfate (AOM/DSS) induced CAC mouse model was established. The CAC mice treated with ABP showed smaller tumor size and lower tumor incidence than untreated ones. ABP increased anti-inflammatory cytokine IL-10, inhibited secretion of pro-inflammatory cytokines (IL-6, IFN-γ, and TNF-α), mitigated oxidative stress by increasing GSH and decreasing MDA levels, suppressed the activation of STAT3 and expressions of its related genes c-Myc and cyclin D1. Moreover, ABP treatment increased the relative abundance of beneficial bacteria (f_Ruminococcaceae, g_Roseburia, g_Odoribacter, g_Oscillospira, and g_Akkermansia) and the levels of fecal short-chain fatty acid (SCFA) in CAC model mice. In summary, our data suggest that ABP could be a potential therapeutic agent for treating CAC.

Impact of bacterial infection and intestinal microbiome on colorectal cancer development

ABSTRACT

Accumulating evidence suggests that intestinal bacteria play an important role in the pathogenesis of colorectal cancer (CRC). Due to the complexity of the intestinal microbiome, identification of the specific causative microbial agents in CRC remains challenging, and the search for the causative microbial agents is intense. However, whether bacteria or their products can induce inflammation that results in tumorigenesis or directly causes CRC in humans is still not clear. This review will mainly focus on the progress of bacterial infection and CRC, and introduce the microbial contribution to the hallmarks of cancer. This article uses Salmonella and its chronic infection as an example to investigate a single pathogen and its role in the development of CRC, based on laboratory and epidemiological evidence. The bacterial infection leads to an altered intestinal microbiome. The review also discusses the dysfunction of the microbiome and the mechanism of host-microbial interactions, for example, bacterial virulence factors, key signaling pathways in the host, and microbial post-translational modifications in the tumorigenesis. Colonic carcinogenesis involves a progressive accumulation of mutations in a genetically susceptible host leading to cellular autonomy. Moving forward, more human data are needed to confirm the direct roles of bacterial infection in CRC development. Insights into the inhibiting infection will help to prevent cancer and develop strategies to restore the balance between host and microorganisms.

Gut microbiota changes and its potential relations with thyroid carcinoma

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Thyroid cancer patients have reduced richness and diversity of gut microbiota.

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A predictive model of 10 genera could distinguish thyroid cancer patients from healthy controls.

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The loss of the short-chain fatty acid-producing bacteria may promote thyroid carcinoma.

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The functional changes that occur in thyroid cancer patients affect the processing of genetic information.

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A four-genus microbial signature may be able to distinguish thyroid carcinoma patients with metastatic lymphadenopathy from those without metastatic lymphadenopathy.

Introduction

Emerging evidence suggests that the essence of life is the ecological balance of the neural, endocrine, metabolic, microbial, and immune systems. Gut microbiota have been implicated as an important factor affecting thyroid homeostasis.

Objectives

This study aims to explore the relationship between gut microbiota and the development of thyroid carcinoma.

Methods

Stool samples were collected from 90 thyroid carcinoma patients (TCs) and 90 healthy controls (HCs). Microbiota were analyzed using 16S ribosomal RNA gene sequencing. A cross-sectional study of an exploratory cohort of 60 TCs and 60 HCs was conducted. The gut microbiota signature of TCs was established by LEfSe, stepwise logistic regression, lasso regression, and random forest model analysis. An independent cohort of 30 TCs and 30 HCs was used to validate the findings. Functional prediction was achieved using Tax4Fun and PICRUSt2. TC patients were subsequently divided into subgroups to analyze the relationship between microbiota and metastatic lymphadenopathy.

Results

In the exploratory cohorts, TCs had reduced richness and diversity of gut microbiota compared to HCs. No significant difference was found between TCs and HCs on the phylum level, though 70% of TCs had increased levels of Proteobacteria-types based on dominant microbiota typing. A prediction model of 10 genera generated with LEfSe analysis and lasso regression distinguished TCs from HCs with areas under the curves of 0.809 and 0.746 in the exploration and validation cohorts respectively. Functional prediction suggested that the microbial changes observed in TCs resulted in a decline in aminoacyl-tRNA biosynthesis, homologous recombination, mismatch repair, DNA replication, and nucleotide excision repair. A four-genus microbial signature was able to distinguish TC patients with metastatic lymphadenopathy from those without metastatic lymphadenopathy.

Conclusion

Our study shows that thyroid carcinoma patients demonstrate significant changes in gut microbiota, which will help delineate the relationship between gut microbiota and TC pathogenesis.

Strategies for the treatment of colorectal cancer caused by gut microbiota

Colorectal cancer (CRC), also named as colon and rectal or bowel cancer, is one of the leading neoplasia diagnosed in the world. Genetic sequencing studies of microorganisms from the intestinal microbiota of patients with CRC revealed that changes in its composition occur with the development of the disease, which can play a fundamental role in its development, being mediated by the production of metabolites and toxins that damage enterocytes. Some microorganisms are frequently reported in the literature as the main agents of this process, such as the bacteria Fusobacterium nucleatum, Escherichia coli and Bacteroides fragilis. Thus, understanding the mechanisms and function of each microorganism in CRC is essential for the development of treatment tools that focus on the gut microbiota. This review verifies current research aimed at evaluating the microorganisms present in the microbiota that can influence the development of CRC, as well as possible forms of treatment that can prevent the initiation and/or spread of this disease. Due to the incidence of CRC, alternatives have been launched considering factors beyond those already known in the disease development, such as diet, fecal microbiota transplantation, use of probiotics and antibiotics, which have been widely studied for this purpose. However, despite being promising, the studies that focus on the development of new therapeutic approaches targeting the microorganisms that cause CRC still need to be improved and better developed, involving new techniques to elucidate the effectiveness and safety of these new methods.

Patients With Common Variable Immunodeficiency (CVID) Show Higher Gut Bacterial Diversity and Levels of Low-Abundance Genes Than the Healthy Housemates

Common variable immunodeficiency (CVID) is a clinically and genetically heterogeneous disorder with inadequate antibody responses and low levels of immunoglobulins including IgA that is involved in the maintenance of the intestinal homeostasis. In this study, we analyzed the taxonomical and functional metagenome of the fecal microbiota and stool metabolome in a cohort of six CVID patients without gastroenterological symptomatology and their healthy housemates. The fecal microbiome of CVID patients contained higher numbers of bacterial species and altered abundance of thirty-four species. Hungatella hathewayi was frequent in CVID microbiome and absent in controls. Moreover, the CVID metagenome was enriched for low-abundance genes likely encoding nonessential functions, such as bacterial motility and metabolism of aromatic compounds. Metabolomics revealed dysregulation in several metabolic pathways, mostly associated with decreased levels of adenosine in CVID patients. Identified features have been consistently associated with CVID diagnosis across the patients with various immunological characteristics, length of treatment, and age. Taken together, this initial study revealed expansion of bacterial diversity in the host immunodeficient conditions and suggested several bacterial species and metabolites, which have potential to be diagnostic and/or prognostic CVID markers in the future.

Pro-biomics: Omics Technologies To Unravel the Role of Probiotics in Health and Disease

The comprehensive characterization of probiotic action has flourished during the past few decades, alongside the evolution of high-throughput, multiomics platforms. The integration of these platforms into probiotic animal and human studies has provided valuable insights into the holistic effects of probiotic supplementation on intestinal and extraintestinal diseases. Indeed, these methodologies have informed about global molecular changes induced in the host and residing commensals at multiple levels, providing a bulk of metagenomic, transcriptomic, proteomic, and metabolomic data. The meaningful interpretation of generated data remains a challenge; however, the maturation of the field of systems biology and artificial intelligence has supported analysis of results. In this review article, we present current literature on the use of multiomics approaches in probiotic studies, we discuss current trends in probiotic research, and examine the possibility of tailor-made probiotic supplementation. Lastly, we delve deeper into newer technologies that have been developed in the last few years, such as single-cell multiomics analyses, and provide future directions for the maximization of probiotic efficacy.

Pectin supplement significantly enhanced the anti-PD-1 efficacy in tumor-bearing mice humanized with gut microbiota from patients with colorectal cancer

Background: Anti-PD-1-based immunotherapy has emerged as a promising therapy for several cancers. However, it only benefits a small subset of colorectal cancer (CRC) patients. Mounting data supports the pivotal role of gut microbiota in shaping immune system. Pectin, a widely consumed soluble fiber, has been reported to ameliorate the imbalance of gut microbiota. Therefore, we aimed to explore the effect and the underlying mechanisms of pectin in improving anti-PD-1 mAb efficacy. Methods: The C57BL/6 mice were treated with a broad-spectrum antibiotic (ATB) cocktail to depleted endogenous gut microbiota and subsequently humanized with feces from healthy controls or newly diagnosed CRC patients. The antitumor efficacies of anti-PD-1 mAb combined with or without pectin were assessed using these mice. Flow cytometry and immunohistochemistry (IHC) were conducted to investigate the tumor immune microenvironment after treatment. The gut microbiota profiles and short-chain fatty acids (SCFAs) levels were determined by 16S ribosomal RNA (16S rRNA) gene sequencing and gas chromatography-mass spectrometry (GC-MS), respectively. The effect of gut microbiota on anti-PD-1 mAb efficacy after pectin supplement was further tested by fecal microbiota transplantation (FMT). Results: The anti-PD-1 mAb efficacy was largely impaired in the mice humanized with feces from newly diagnosed CRC patients compared to those from healthy controls. However, pectin significantly enhanced the anti-PD-1 mAb efficacy in the tumor-bearing mice humanized with CRC patient gut microbiota. Flow cytometry and IHC analysis revealed increased T cell infiltration and activation in the tumor microenvironment of mice treated with anti-PD-1 mAb plus pectin. In vivo depletion of CD8⁺ T cells diminished the anti-tumor effect of anti-PD-1 mAb combined with pectin. 16S rRNA gene sequencing showed that pectin significantly increased gut microbial diversity and beneficially regulated microbial composition. In addition, we identified unique bacterial modules that were significantly enriched in the anti-PD-1 mAb + pectin group, which composed of butyrate-producing bacteria indicative of good response to immunotherapy. Meanwhile, GC-MS showed that pectin altered the level of SCFA butyrate. Furthermore, butyrate, a main product of dietary fiber in gut microbial fermentation, was found to be sufficient to promote T cells infiltration and thus enhance the efficacy of anti-PD-1 mAb. In addition, FMT demonstrated the effects of pectin were dependent on gut microbiota. Importantly, the beneficial effects of pectin were confirmed in the mice humanized with gut microbiota from patient with resistance to anti-PD-1 mAb. Conclusion: Pectin facilitated the anti-PD-1 mAb efficacy in CRC via regulating the T cell infiltration in the tumor microenvironment, which was potentially mediated by the metabolite butyrate.

Association Between Gut Microbiome and Frailty in the Older Adult Population in Korea

Frailty is a common geriatric syndrome associated with the risk of adverse health outcomes. Recently, 2 key pathophysiological characteristics of frailty, altered energy metabolism and dysregulated immunity, have been reported to be associated with gut microbiome dysbiosis, indicating that the gut microbiome plays a role in frailty. However, few studies have directly examined the relationship between the gut microbiome and frailty. Here, we investigated the association of frailty measures with the gut microbiome using 16S rRNA gene sequencing data obtained from the fecal samples of 176 Korean older adults. Overall frailty was scored using the Korean Frailty Index (FI). Grip strength and Geriatric Depression Scale (GDS) scores were used as physical and mental frailty measures, respectively. In contrast to age, metabolic, and inflammatory biomarkers, the frailty measures were associated with interindividual variations in microbial composition (false discovery rate [FDR] < 0.2). Both FI and GDS scores were negatively associated with microbial diversity (FDR < 0.2). Frailty measures showed distinct associations with specific microbial taxa and metabolic functions. Particularly, the Bacteroides enterotype was found only in subjects categorized in the frail group. Moreover, we observed that the abundance of beneficial taxa, such as Prevotella copri and Coprococcus eutactus, was reduced in frailer individuals, whereas that of detrimental taxa, such as Bacteroides fragilis and Clostridium hathewayi, was increased (FDR < 0.2). Our findings suggest that the gut microbiome can be used an indicator of an increased risk of frailty or a target for improving health in frail older adults.

Harnessing Tissue Engineering Tools to Interrogate Host-Microbiota Crosstalk in Cancer

Recent studies have begun to highlight the diverse and tumor-specific microbiomes across multiple cancer types. We believe this work raises the important question of whether the classical "Hallmarks of Cancer" should be expanded to include tumor microbiomes. To answer this question, the causal relationships and co-evolution of these microbiotic tumor ecosystems must be better understood. Because host-microbe interactions should be studied in a physiologically relevant context, animal models have been preferred. Yet these models are often poor mimics of human tumors and are difficult to interrogate at high spatiotemporal resolution. We believe that in vitro tissue engineered platforms could provide a powerful alternative approach that combines the high-resolution of in vitro studies with a high degree of physiological relevance. This review will focus on tissue engineered approaches to study host-microbe interactions and to establish their role as an emerging hallmark of cancer with potential as a therapeutic target.

Anaerobic bacterial communities associated with oral carcinoma: Intratumoral, surface-biofilm and salivary microbiota

It was estimated that more than 700 bacterial species inhabit the oral cavity of healthy humans. Anaerobes comprise a significant fraction of the oral bacteriome and play an important role in the formation of multi-species biofilms attached to various anatomical sites. Bacterial biofilms are also associated with pathologic laesions of the oral cavity, including oral squamous cell carcinoma (OSCC), and distinct oral taxa could also be detected within the tumors, i.e. in deep biopsy samples. These observations suggested that certain oral bacteria or oral bacterial communities may play a causative role in oral carcinogenesis, in addition to the well characterized risk factors of oral cancer. Alternatively, it was also proposed that a subset of oral bacteria may have a growth advantage in the unique microenvironment of OSCC. Recently, a series of studies analysed the OSCC-associated bacterial communities using metataxonomic, metagenomic and metatranscriptomic approaches. This review outlines the major differences between the community structure of microbiota in tumor biopsy, surface-biofilm and salivary or oral wash samples collected from OSCC patients, compared to corresponding samples from control persons. A special emphasis is given to the anaerobic bacteria Fusobacterium nucleatum and Fusobacterium periodonticum that were characterised repeatedly as "OSCC-associated" in independent studies. Predicted microbial functions and relevant in vivo experimental models of oral carcinogenesis will also be summarized.