Inflammatory Bacteriome and Oral Squamous Cell Carcinoma

Association Between Oral Microbiota and Cigarette Smoking in the Chinese Population

The oral microbiota has been observed to be influenced by cigarette smoking and linked to several human diseases. However, research on the effect of cigarette smoking on the oral microbiota has not been systematically conducted in the Chinese population. We profiled the oral microbiota of 316 healthy subjects in the Chinese population by 16S rRNA gene sequencing. The alpha diversity of oral microbiota was different between never smokers and smokers (P = 0.002). Several bacterial taxa were first reported to be associated with cigarette smoking by LEfSe analysis, including Moryella (q = 1.56E-04), Bulleidia (q = 1.65E-06), and Moraxella (q = 3.52E-02) at the genus level and Rothia dentocariosa (q = 1.55E-02), Prevotella melaninogenica (q = 8.48E-08), Prevotella pallens (q = 4.13E-03), Bulleidia moorei (q = 1.79E-06), Rothia aeria (q = 3.83E-06), Actinobacillus parahaemolyticus (q = 2.28E-04), and Haemophilus parainfluenzae (q = 4.82E-02) at the species level. Two nitrite-producing bacteria that can increase the acidity of the oral cavity, Actinomyces and Veillonella, were also enriched in smokers with FDR-adjusted q-values of 3.62E-06 and 1.10E-06, respectively. Notably, we observed that two acid production-related pathways, amino acid-related enzymes (q = 6.19E-05) and amino sugar and nucleotide sugar metabolism (q = 2.63E-06), were increased in smokers by PICRUSt analysis. Finally, the co-occurrence analysis demonstrated that smoker-enriched bacteria were significantly positively associated with each other and were negatively correlated with the bacteria decreased in smokers. Our results suggested that cigarette smoking may affect oral health by creating a different environment by altering bacterial abundance, connections among oral microbiota, and the microbiota and their metabolic function.

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.

The Oral Microbiome and Cancer

There is mounting evidence that members of the human microbiome are highly associated with a wide variety of cancer types. Among oral cancers, oral squamous cell carcinoma (OSCC) is the most prevalent and most commonly studied, and it is the most common malignancy of the head and neck worldwide. However, there is a void regarding the role that the oral microbiome may play in OSCC. Previous studies have not consistently found a characteristic oral microbiome composition associated with OSCC. Although a direct causality has not been proven, individual members of the oral microbiome are capable of promoting various tumorigenic functions related to cancer development. Two prominent oral pathogens, Porphyromonas gingivalis, and Fusobacterium nucleatum can promote tumor progression in mice. P. gingivalis infection has been associated with oro-digestive cancer, increased oral cancer invasion, and proliferation of oral cancer stem cells. The microbiome can influence the evolution of the disease by directly interacting with the human body and significantly altering the response and toxicity to various forms of cancer therapy. Recent studies have shown an association of certain phylogenetic groups with the immunotherapy treatment outcomes of certain tumors. On the other side of the coin, recently it has been a resurgence in interest on the potential use of bacteria to cure cancer. These kinds of treatments were used in the late nineteenth and early twentieth centuries as the first line of defense against cancer in some hospitals but later displaced by other types of treatments such as radiotherapy. Currently, organisms such as Salmonella typhimurium and Clostridium spp. have been used for targeted strategies as potential vectors to treat cancer. In this review, we briefly summarize our current knowledge of the role of the oral microbiome, focusing on its bacterial fraction, in cancer in general and in OSCC more precisely, and a brief description of the potential use of bacteria to target tumors.

Update and review of the gerodontology prospective for 2020's: Linking the interactions of oral (hypo)-functions to health vs. systemic diseases

New lines of evidence suggest that the oral-systemic medical links and oral hypo-function are progressively transcending beyond the traditional clinical signs and symptoms of oral diseases. Research into the dysbiotic microbiome, host immune/inflammatory regulations and patho-physiologic changes and subsequent adaptations through the oral-systemic measures under ageism points to pathways leading to mastication deficiency, dysphagia, signature brain activities for (neuro)-cognition circuitries, dementia and certain cancers of the digestive system as well. Therefore, the coming era of oral health-linked systemic disorders will likely reshape the future of diagnostics in oral geriatrics, treatment modalities and professional therapies in clinical disciplines. In parallel to these highlights, a recent international symposium was jointly held by the International Association of Gerontology and Geriatrics (IAGG), Japanese Society of Gerodontology (JSG), the representative of USA and Taiwan Academy of Geriatric Dentistry (TAGD) on Oct 25th, 2019. Herein, specific notes are briefly addressed and updated for a summative prospective from this symposium and the recent literature.

Increased Expression of SHMT2 Is Associated With Poor Prognosis and Advanced Pathological Grade in Oral Squamous Cell Carcinoma

This study focused on the expression of mitochondrial serine hydroxymethyltransferase (SHMT2) in oral squamous cell carcinoma (OSCC) and its correlation with clinical traits and the prognosis of OSCC patients. Immunochemical staining and Western blotting were used to quantify the expression of SHMT2 and related immune markers in OSCC. Using OSCC microarrays and The Cancer Genome Atlas (TCGA) database, we evaluated the association between SHMT2 and various clinical traits. We found that increased expression of SHMT2 was detected in OSCC and correlated with advanced pathological grade and recurrence of OSCC. By a multivariate Cox proportional hazard model, high expression of SHMT2 was shown to indicate a negative prognosis. In addition, in the OSCC microenvironment, increasing the expression of SHMT2 was associated with high expression levels of programmed cell death-ligand 1 (PD-L1), CKLF-like MARVEL transmembrane domain containing 6 (CMTM6), V-type immunoglobulin domain-containing suppressor (VISTA), B7-H4, Slug, and CD317. In the future, more effort will be required to investigate the role of SHMT2 in the OSCC microenvironment.

The Human Microbiome in Relation to Cancer Risk: A Systematic Review of Epidemiologic Studies

The microbiome has been hypothesized to play a role in cancer development. Because of the diversity of published data, an overview of available epidemiologic evidence linking the microbiome with cancer is now needed. We conducted a systematic review using a tailored search strategy in Medline and EMBASE databases to identify and summarize the current epidemiologic literature on the relationship between the microbiome and different cancer outcomes published until December 2019. We identified 124 eligible articles. The large diversity of parameters used to describe microbial composition made it impossible to harmonize the different studies in a way that would allow meta-analysis, therefore only a qualitative description of results could be performed. Fifty studies reported differences in the gut microbiome between patients with colorectal cancer and various control groups. The most consistent findings were for Fusobacterium, Porphyromonas, and Peptostreptococcus being significantly enriched in fecal and mucosal samples from patients with colorectal cancer. For the oral microbiome, significantly increased and decreased abundance was reported for Fusobacterium and Streptococcus, respectively, in patients with oral cancer compared with controls. Overall, although there was a large amount of evidence for some of these alterations, most require validation in high-quality, preferably prospective, epidemiologic studies.

Role of Oral Bacteria in the Development of Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is an invasive epithelial neoplasm that is influenced by various risk factors, with a low survival rate and an increasing death rate. In the past few years, with the verification of the close relationship between different types of cancers and the microbiome, research has focused on the compositional changes of oral bacteria and their role in OSCC. Generally, oral bacteria can participate in OSCC development by promoting cell proliferation and angiogenesis, influencing normal apoptosis, facilitating invasion and metastasis, and assisting cancer stem cells. The study findings on the association between oral bacteria and OSCC may provide new insight into methods for early diagnosis and treatment development.

Involvement of Fusobacterium Species in Oral Cancer Progression: A Literature Review Including Other Types of Cancer

Chronic inflammation caused by infections has been suggested to be one of the most important cause of cancers. It has recently been shown that there is correlation between intestinal bacteria and cancer development including metastasis. As over 700 bacterial species exist in an oral cavity, it has been concerning that bacterial infection may cause oral cancer. However, the role of bacteria regarding tumorigenesis of oral cancer remains unclear. Several papers have shown that Fusobacterium species deriving the oral cavities, especially, play a crucial role for the development of colorectal and esophageal cancer. F. nucleatum is a well-known oral bacterium involved in formation of typical dental plaque on human teeth and causing periodontal diseases. The greatest characteristic of F. nucleatum is its ability to adhere to various bacteria and host cells. Interestingly, F. nucleatum is frequently detected in oral cancer tissues. Moreover, detection of F. nucleatum is correlated with the clinical stage of oral cancer. Although the detailed mechanism is still unclear, Fusobacterium species have been suggested to be associated with cell adhesion, tumorigenesis, epithelial-to-mesenchymal transition, inflammasomes, cell cycle, etc. in oral cancer. In this review, we introduce the reports focused on the association of Fusobacterium species with cancer development and progression including oral, esophageal, and colon cancers.

Association or Causation? Exploring the Oral Microbiome and Cancer Links

Several epidemiological investigations have found associations between poor oral health and different types of cancer, including colorectal, lung, pancreatic, and oral malignancies. The oral health parameters underlying these relationships include deficient oral hygiene, gingival bleeding, and bone and tooth loss. These parameters are related to periodontal diseases, which are directly and indirectly mediated by oral bacteria. Given the increased accessibility of microbial sequencing platforms, many recent studies have investigated the link between the oral microbiome and these cancers. Overall, it seems that oral dysbiotic states can contribute to tumorigenesis in the oral cavity as well as in distant body sites. Further, it appears that certain oral bacterial species can contribute to carcinogenesis, in particular, Fusobacterium nucleatum and Porphyromonas gingivalis, based on results from epidemiological as well as mechanistic studies. Yet, the strength of the findings from these investigations is hampered by the heterogeneity of the methods used to measure oral diseases, the treatment of confounding factors, the study design, the platforms employed for microbial analysis, and types of samples analyzed. Despite these limitations, there is an overall indication that the presence of oral dysbiosis that leads to oral diseases may directly and/or indirectly contribute to carcinogenesis. Proper methodological standardized approaches should be implemented in future epidemiological studies as well as in the mechanistic investigations carried out to explore these results.

Dysbiosis of salivary microbiome and cytokines influence oral squamous cell carcinoma through inflammation

Advanced combinatorial treatments of surgery, chemotherapy, and radiotherapy do not have any effect on the enhancement of a 5-year survival rate of oral squamous cell carcinoma (OSCC). The discovery of early diagnostic non-invasive biomarkers is required to improve the survival rate of OSCC patients. Recently, it has been reported that oral microbiome has a significant contribution to the development of OSCC. Oral microbiome induces inflammatory response through the production of cytokines and chemokines that enhances tumor cell proliferation and survival. The study aims to develop saliva-based oral microbiome and cytokine biomarker panel that screen OSCC patients based on the level of the microbiome and cytokine differences. We compared the oral microbiome signatures and cytokine level in the saliva of OSCC patients and healthy individuals by 16S rRNA gene sequencing targeting the V3/V4 region using the MiSeq platform and cytokine assay, respectively. The higher abundance of Prevotella melaninogenica, Fusobacterium sp., Veillonella parvula, Porphyromonas endodontalis, Prevotella pallens, Dialister, Streptococcus anginosus, Prevotella nigrescens, Campylobacter ureolyticus, Prevotella nanceiensis, Peptostreptococcus anaerobius and significant elevation of IL-8, IL-6, TNF-α, GM-CSF, and IFN-γ in the saliva of patients having OSCC. Oncobacteria such as S. anginosus, V. parvula, P. endodontalis, and P. anaerobius may contribute to the development of OSCC by increasing inflammation via increased expression of inflammatory cytokines such as IL-6, IL-8, TNF-α, IFN-γ, and GM-CSF. These oncobacteria and cytokines panels could potentially be used as a non-invasive biomarker in clinical practice for more efficient screening and early detection of OSCC patients.

Oral microbiota alteration associated with oral cancer and areca chewing

Oral cancer is among most common neoplasm of oral cavity; in many cases, it develops at the site of premalignant lesion. Areca nut has been identified as a carcinogen, which was proved to promote the inflammation level and contributes to oral malignancy. Chewing areca nut is the main cause of the premalignant disease oral submucous fibrosis (OSF). Bacterial alterations were suggested to be assonated with oral cancer progression. Therefore, the present study was carried out to determine the changes of microbiota in the mucosa along stage of development of oral cancer with areca nut chewing. 162 participants, reporting to department of oral medical center, were enrolled into the study which includes 45 patients each of OSF, 42 of oral cancer, 29 healthy controls (HC) with areca nut chewing, and 46 healthy controls (HC) never chewing areca nut. Oral swabbing of tongue dorsum, buccal mucosa, and gingiva was evaluated by MiSeq platform of the V3-V4 region of the 16S rRNA gene. These data revealed microbial changes that may mirror oral cancer progression and reflect clinical preconditions such as areca nut chewing. Consequently, revealing microbial changes in patients with oral squamous cell carcinomas and the premalignant disease oral submucous fibrosis (OSF) with areca nut chewing might improve our understanding of the pathobiology of the disease and help in the design of novel diagnostic and treatment strategies.

Tongue microbiome of smokeless tobacco users

Background

The possibility that smokeless tobacco may contribute to oral carcinogenesis by influencing the oral microbiome has not been explored. This preliminary cross-sectional study sought to assess the effect of using shammah, a form of smokeless tobacco prevalent in Arabia, on the tongue microbiome. Tongue scarping samples were obtained from 29 shammah users (SU; 27.34 ± 6.9 years) and 23 shammah non-users (SNU; 27.7 ± 7.19 years) and analyzed with 16S rRNA gene sequencing (V1-V3). Species-level taxonomy assignment of the high-quality, merged reads was obtained using a previously described BLASTn-based algorithm. Downstream analyses were performed with QIIME, LEfSe, and R.

Results

A total of 178 species, belonging to 62 genera and 8 phyla were identified. Genera Streptococcus, Leptotrichia, Actinomyces, Veillonella, Haemophilus, Prevotella and Neisseria accounted for more than 60% of the average microbiome. There were no differences between the two groups in species richness and alpha-diversity, but PCoA showed significant separation (P = 0.015, ANOSIM). LEfSe analysis identified 22 species to be differentially abundant between the SU and SNU. However, only 7 species maintained a false discovery rate of ≤0.2 and could cluster the two groups separately: Rothia mucilaginosa, Streptococcus sp. oral taxon 66, Actinomyces meyeri, Streptococcus vestibularis Streptococcus sanguinis and a potentially novel Veillonella species in association with SU, and Oribacterium asaccharolyticum with SNU.

Conclusion

These preliminary results indicate that shammah use induces tongue microbiome changes including enrichment of several species with high acetaldehyde production potential, which warrants further investigation.

High-throughput nucleotide sequencing for bacteriome studies in oral squamous cell carcinoma: a systematic review

PURPOSE

Dysbiosis has been identified in oral squamous cell carcinoma (OSCC). The aim of this study was to carry out a systematic review of an electronic research that was carried out on articles published between January 2008 and September 2018.

METHODS

Eight studies were selected after applying the inclusion and exclusion criteria.

RESULTS

All articles targeted the hypervariable regions of the 16S rRNA gene. At the phylum level, it was found reduction of Bacteroidetes (2/8 studies) and increase of Firmicutes (2/8 studies). At the genus level, Rothia increased (1/8 studies) and decreased (2/8 studies) in tumor samples, and Streptococcus also was found increased (3/8 studies) and reduced (3/8 studies). Fusobacterium only increased in OSCC samples (3/8 studies). At species level, an increase in F. nucleatum subsp. polymorphum was more associated to OSCC (2/8 studies) than with controls, as was P. aeruginosa (3/8 studies).

CONCLUSION

In summary, the results corroborated dysbiosis in OSCC patients, with enrichment of microbial taxa that are associated with inflammation and production of acetaldehyde. However, variations of study design and sample size were observed among the studies, as well as a shortage of more detailed analyses of possible correlations between risk habits and OSCC. This lack of more detailed analysis may be the cause of the inconsistencies in regard of the alterations reported for certain genera and species. In conclusion, there is an association between OSCC and oral microbiota dysbiosis, but its role in oral carcinogenesis needs to be clarified in more detail.

Characterization of the Esophageal Microbiota and Prediction of the Metabolic Pathways Involved in Esophageal Cancer

Esophageal microbiota plays important roles in esophageal cancer. Esophagectomy, as the most important therapeutic way, contributes to changes of esophageal microbiome. However, there are few studies examining the esophageal microbiome and the metabolic changes before and after esophagectomy. The present study characterized the esophageal microbiome of 17 patients with esophageal squamous cell carcinoma (ESCC), 11 patients with esophagogastric junction (EGJ) cancer, 15 patients at 9–12 months after radical esophagectomy and 16 healthy controls (HC). 16S ribosomal RNA gene sequencing was used to evaluate the microbiome and predict the metabolic pathways. Our results showed that the microbial diversity was significantly lower in ESCC, EGJ and post-ESCC groups than that in the HC group. The abundance of Fusobacteria was higher (7.01 vs. 1.12%, P = 0.039) and the abundance of Actinobacteria (1.61 vs. 4.04%) was lower in the ESCC group than that in the HC group. We found significant differences in the abundance of Bacteroidetes (20.45 vs. 9.86%, P = 0.026), Fusobacteria (7.01 vs. 1.66%, P = 0.030) between ESCC and post-ESCC groups. The results of microbial composition analysis and PICRUSt demonstrated significant differences between ESCC and HC groups. The β diversity and PICRUSt suggested that the microbial composition and metabolic pathways were similar to HC group after esophagectomy. The monitoring of the esophagus microbiota may be an essential method to predict the recurrence of tumor.

Composition and function of oral microbiota between gingival squamous cell carcinoma and periodontitis

OBJECTIVES

Previous studies have proved that periodontitis is an independent risk factor of oral squamous cell carcinoma (OSCC) epidemiologically. Along with the important role of microbiota in the cancer process and the specific anatomical position, our study explored the microbial composition and functions in periodontitis and gingival squamous cell carcinoma (GSCC).

MATERIALS AND METHODS

GSCC patients (n = 10), matched periodontitis patients (n = 15), and healthy individuals (n = 15) were recruited. Saliva, subgingival plaque, tongue dorsum, buccal mucosa, cancerous tissue, and paracancerous tissue samples were collected. 16S rDNA amplicon sequencing and functional prediction were applied for the taxonomic analysis.

RESULTS

Periodontal pathogens occupied 46% in GSCC. Besides, the mutual operational taxonomy unites (OTU) generated from the subgingival plaque occupied 38.36% and 44.13% from saliva. Fusobacterium, Peptostreptococcus, and Prevotella were more abundant in cancerous tissues, while Streptococcus, Neisseria, and Haemophilus were more enriched in saliva or soft mucosa. PCoA exhibited similar cluster between tongue dorsum and saliva in GSCC. GSCC showed lower richness than periodontitis. In saliva and subgingival plaque, Atopobium was more prevalent in GSCC than periodontitis and controls in descending order. Lipopolysaccharide (LPS) biosynthesis increased in subgingival plaque of GSCC compared with the other two groups.

CONCLUSION

Periodontal pathogens were abundant in GSCC. Cancerous tissues harbor enriched periodontal pathogens while saliva or soft mucosa harbored more periodontal health related bacteria. A high level of Atopobium in saliva and LPS biosynthesis have the potential for increasing the risk of suffering from GSCC in individuals with periodontitis, which needs more evidence to clarify it.

Commensal Oral Rothia mucilaginosa Produces Enterobactin, a Metal-Chelating Siderophore

Next-generation sequencing studies of saliva and dental plaque from subjects in both healthy and diseased states have identified bacteria belonging to the Rothia genus as ubiquitous members of the oral microbiota. To gain a deeper understanding of molecular mechanisms underlying the chemical ecology of this unexplored group, we applied a genome mining approach that targets functionally important biosynthetic gene clusters (BGCs). All 45 genomes that were mined, representing Rothia mucilaginosa, Rothia dentocariosa, and Rothia aeria, harbored a catechol-siderophore-like BGC. To explore siderophore production further, we grew the previously characterized R. mucilaginosa ATCC 25296 in liquid cultures, amended with glycerol, which led to the identification of the archetype siderophore enterobactin by using tandem liquid chromatography-mass spectrometry (LC-MS/MS), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance (NMR) spectroscopy. Normally attributed to pathogenic gut bacteria, R. mucilaginosa is the first commensal oral bacterium found to produce enterobactin. Cocultivation studies including R. mucilaginosa or purified enterobactin revealed that enterobactin reduced growth of certain strains of cariogenic Streptococcus mutans and pathogenic strains of Staphylococcus aureus Commensal oral bacteria were either unaffected, reduced in growth, or induced to grow adjacent to enterobactin-producing R. mucilaginosa or the pure compound. Taken together with Rothia's known capacity to ferment a variety of carbohydrates and amino acids, our findings of enterobactin production add an additional level of explanation to R. mucilaginosa's prevalence in the oral cavity. Enterobactin is the strongest Fe(III) binding siderophore known, and its role in oral health requires further investigation.IMPORTANCE The communication language of the human oral microbiota is vastly underexplored. However, a few studies have shown that specialized small molecules encoded by BGCs have critical roles such as in colonization resistance against pathogens and quorum sensing. Here, by using a genome mining approach in combination with compound screening of growth cultures, we identified that the commensal oral community member R. mucilaginosa harbors a catecholate-siderophore BGC, which is responsible for the biosynthesis of enterobactin. The iron-scavenging role of enterobactin is known to have positive effects on the host's iron pool and negative effects on host immune function; however, its role in oral health remains unexplored. R. mucilaginosa was previously identified as an abundant community member in cystic fibrosis, where bacterial iron cycling plays a major role in virulence development. With respect to iron's broad biological importance, iron-chelating enterobactin may explain R. mucilaginosa's colonization success in both health and disease.

Acetaldehyde production by Rothia mucilaginosa isolates from patients with oral leukoplakia

Rothia mucilaginosa has been found at high abundance on oral leukoplakia (OLK). The ability of clinical isolates to produce acetaldehyde (ACH) from ethanol has not been investigated. The objective of the current study was to determine the capacity of R. mucilaginosa isolates recovered from OLK to generate ACH. Analysis of R. mucilaginosa genomes (n = 70) shows that this species does not normally encode acetaldehyde dehydrogenase (ALDH) required for detoxification of ACH. The predicted OLK metagenome also exhibited reduced ALDH coding capacity. We analysed ACH production in 8 isolates of R. mucilaginosa and showed that this species is capable of generating ACH in the presence of ethanol. The levels of ACH produced (mean = 53 µM) were comparable to those produced by Neisseria mucosa and Candida albicans in parallel assays. These levels were demonstrated to induce oxidative stress in cultured oral keratinocytes. This study shows that R. mucilaginosa can generate ACH from ethanol in vitro at levels which can induce oxidative stress. This organism likely contributes to oral ACH levels following alcohol consumption and the significance of the increased abundance of R. mucilaginosa in patients with potentially malignant disorders requires further investigation.

From Beyond the Pale to the Pale Riders: The Emerging Association of Bacteria with Oral Cancer

Oral cancer, predominantly oral squamous cell carcinoma (OSCC), is the eighth-most common cancer worldwide, with a 5-y survival rate <50%. There are numerous risk factors for oral cancer, among which periodontal disease is gaining increasing recognition. The creation of a sustained dysbiotic proinflammatory environment by periodontal bacteria may serve to functionally link periodontal disease and oral cancer. Moreover, traditional periodontal pathogens, such as Porphyromonas gingivalis, Fusobacterium nucleatum, and Treponema denticola, are among the species most frequently identified as being enriched in OSCC, and they possess a number of oncogenic properties. These organisms share the ability to attach and invade oral epithelial cells, and from there each undergoes its own unique molecular dialogue with the host epithelium, which ultimately converges on acquired phenotypes associated with cancer, including inhibition of apoptosis, increased proliferation, and activation of epithelial-to-mesenchymal transition leading to increased migration of epithelial cells. Additionally, emerging properties of structured bacterial communities may increase oncogenic potential, and consortia of P. gingivalis and F. nucleatum are synergistically pathogenic within in vivo oral cancer models. Interestingly, however, some species of oral streptococci can antagonize the phenotypes induced by P. gingivalis, indicating functionally specialized roles for bacteria in oncogenic communities. Transcriptomic data support the concept that functional, rather than compositional, properties of oral bacterial communities have more relevance to cancer development. Collectively, the evidence is consistent with a modified polymicrobial synergy and dysbiosis model for bacterial involvement in OSCC, with driver mutations generating a conducive microenvironment on the epithelial boundary, which becomes further dysbiotic by the synergistic action of bacterial communities.

Detection of Fusobacterium in oral and head and neck cancer samples: A systematic review and meta-analysis

AIMS

This systematic review aimed to analyse: a) the presence and the abundance of Fusobacterium; b) the Fusobacterium species most often found, and c) the most common methods used for their identification in oral/head and neck cancer samples.

DESIGN

A protocol was registered on PROSPERO database. This review was conducted following PRISMA guidelines. Literature search was performed on five electronic biomedical databases, namely Pubmed, Scopus, Web of Science, Embase, and Cochrane from their start dates to 30 August 2018. Two reviewers independently assessed the eligibility for inclusion; extracted the data; and evaluated the risk of bias.

RESULTS

From 118 unique abstract records, 88 full-text articles were assessed for eligibility. According to inclusion and exclusion criteria, 17 publications were included in this review. Meta-analysis showed an increased prevalence of 6 % (95 % CI, 3-9) of Fusobacterium in tumour lesions than in non-tumour lesions (Fusobacterium prevalence of 16 % in tumour lesions and of 10 % in non-tumour lesions), and a 2.93 higher chance of Fusobacterium being present in tumour lesions (95 % CI, 1.47-5.81). The most common detection methods were based on molecular evidence (64.70 %) (95 % CI, 37.7-84.7). F. nucleatum was the most prevalent species (47.06 %) (95 % CI, 23.5-72).

CONCLUSION

In conclusion, Fusobacterium is present and in higher abundance in oral/head and neck cancer samples when compared to non-cancer samples, suggesting that Fusobacterium may contribute to oral/head and neck cancer development.

The Oral Microbiota May Have Influence on Oral Cancer

The oral microbiota plays an important role in the human microbiome and human health, and imbalances between microbes and their hosts can lead to oral and systemic diseases and chronic inflammation, which is usually caused by bacteria and contributes to cancer. There may be a relationship between oral bacteria and oral squamous cell carcinoma (OSCC); however, this relationship has not been thoroughly characterized. Therefore, in this study, we compared the microbiota compositions between tumor sites and opposite normal tissues in buccal mucosal of 50 patients with OSCC using the 16S rDNA sequencing. Richness and diversity of bacteria were significantly higher in tumor sites than in the control tissues. Cancer tissues were enriched in six families (Prevotellaceae, Fusobacteriaceae, Flavobacteriaceae, Lachnospiraceae, Peptostreptococcaceae, and Campylobacteraceae) and 13 genera, including Fusobacterium, Alloprevotella and Porphyromonas. At the species level, the abundances of Fusobacterium nucleatum, Prevotella intermedia, Aggregatibacter segnis, Capnocytophaga leadbetteri, Peptostreptococcus stomatis, and another five species were significantly increased, suggesting a potential association between these bacteria and OSCC. Furthermore, the functional prediction revealed that genes involved in bacterial chemotaxis, flagellar assembly and lipopolysaccharide (LPS) biosynthesis which are associated with various pathological processes, were significantly increased in the OSCC group. Overall, oral bacterial profiles showed significant difference between cancer sites and normal tissue of OSCC patients, which might be onsidered diagnostic markers and treatment targets. Our study has been registered in the Chinese clinical trial registry (ChiCTR1900025253, http://www.chictr.org.cn/index.aspx).

The Oral Microbiome and Cancer

There is mounting evidence that members of the human microbiome are highly associated with a wide variety of cancer types. Among oral cancers, oral squamous cell carcinoma (OSCC) is the most prevalent and most commonly studied, and it is the most common malignancy of the head and neck worldwide. However, there is a void regarding the role that the oral microbiome may play in OSCC. Previous studies have not consistently found a characteristic oral microbiome composition associated with OSCC. Although a direct causality has not been proven, individual members of the oral microbiome are capable of promoting various tumorigenic functions related to cancer development. Two prominent oral pathogens, Porphyromonas gingivalis, and Fusobacterium nucleatum can promote tumor progression in mice. P. gingivalis infection has been associated with oro-digestive cancer, increased oral cancer invasion, and proliferation of oral cancer stem cells. The microbiome can influence the evolution of the disease by directly interacting with the human body and significantly altering the response and toxicity to various forms of cancer therapy. Recent studies have shown an association of certain phylogenetic groups with the immunotherapy treatment outcomes of certain tumors. On the other side of the coin, recently it has been a resurgence in interest on the potential use of bacteria to cure cancer. These kinds of treatments were used in the late nineteenth and early twentieth centuries as the first line of defense against cancer in some hospitals but later displaced by other types of treatments such as radiotherapy. Currently, organisms such as Salmonella typhimurium and Clostridium spp. have been used for targeted strategies as potential vectors to treat cancer. In this review, we briefly summarize our current knowledge of the role of the oral microbiome, focusing on its bacterial fraction, in cancer in general and in OSCC more precisely, and a brief description of the potential use of bacteria to target tumors.

Fusobacterium nucleatum Caused DNA Damage and Promoted Cell Proliferation by the Ku70/p53 Pathway in Oral Cancer Cells

Bacterial infection influences genomic stability and integrity by causing DNA damage, which increases the possibility of tumor initiation and development. We aimed to investigate whether Fusobacterium nucleatum, one of the periodontal pathogens, promoted oral squamous cell carcinoma (OSCC) by causing DNA double-strand break (DSB). Tca8113 tongue squamous cell carcinoma cells were infected with F. nucleatum. The expression of γH2AX was detected by western blots and immunofluorescence. The proliferation and cell cycle alterations were tested by CCK8 and flow cytometry, respectively. The expression levels of Ku70, p53, and p27 were evaluated by quantitative real-time polymerase chain reaction and western blots. A plasmid was used for the overexpression of Ku70 to verify the possible relationship between Ku70 and p53. We confirmed the presence of DSBs in the response to F. nucleatum by detecting the expression of γH2AX. The cell proliferation ability was increased with an accelerated cell cycle while the expression of p27 was decreased. Meanwhile, the expression of Ku70 and wild p53 was downregulated. When Ku70 was overexpressed, the expression of wild p53 in response to F. nucleatum infection was upregulated and cell proliferation was accordingly inhibited. We concluded that F. nucleatum infection promoted the proliferation ability of Tca8113 by causing DNA damage via the Ku70/p53 pathway.

CD103+ T and Dendritic Cells Indicate a Favorable Prognosis in Oral Cancer

T cells and dendritic cells (DCs) that are positive for the tissue-resident marker CD103 play a vital role in antitumor immunity. In this study, multiplexed immunohistochemistry was applied to stain CD103 and the T-cell marker CD8 as well as the DC marker CD11c on formalin-fixed, paraffin-embedded oral squamous cell carcinoma (OSCC) tissues. Then, the density of CD103⁺CD8⁺ and CD103⁺CD11c⁺ tumor-infiltrating lymphocytes (TILs) in the intratumoral and stromal regions was calculated, and the correlation of CD103⁺CD8⁺ TIL and CD103⁺CD11c⁺ TIL density with OSCC patient prognosis was analyzed. The results revealed that CD103⁺CD8⁺ TILs and CD103⁺CD11c⁺ TILs were abundant in the stromal region and that increased stromal CD103⁺CD8⁺ TIL and intratumoral CD103⁺CD11c⁺ TIL density indicated a favorable prognosis. Moreover, we freshly isolated TILs from OSCC samples and performed flow cytometry to verify that CD103⁺CD8⁺ TILs display a tissue-resident memory T-cell (Trm) phenotype, and we discriminated CD103⁺CD11c⁺ TILs from tumor-associated macrophages.

The Oral Mouse Microbiome Promotes Tumorigenesis in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is the most common malignancy of the head and neck worldwide. Dysbiosis of the microbiome has increasingly been linked to the development of different kinds of cancer. Applying 16S rRNA gene sequence analysis and metatranscriptomic analyses, we characterized the longitudinal changes in the profiles and the function of the oral microbiome in a 4-nitroquinoline-1-oxide (4-NQO)-induced model of OSCC in gnotobiotic mice. We characterized the dynamics of the oral microbiome in this model using two different microbiome inocula: one from healthy mice and the other from mice bearing a 4-NQO-induced tumor. Mice colonized with different oral microbiomes and exposed to 4-NQO had increased tumor numbers and sizes compared to controls exposed to 4-NQO but lacking a microbiome. We observed an overall increase in diversity in the tumorigenic samples compared to that in the nontumor group not exposed to 4-NQO. Despite the variability in community dynamics, specific patterns emerged during the progression of the disease. In the two groups that were inoculated with the OSCC-associated microbiome, we observed opposite profiles of abundance in Parabacteroides and Corynebacterium While the percentage of Parabacteroides bacteria decreased in the control group, it increased in the OSCC group, and the opposite was observed for Corynebacterium The metatranscriptomic analysis revealed overexpression of the same metabolic signatures associated with OSCC regardless of the community profile. These included nitrogen transport, response to stress, interspecies interactions, Wnt pathway modulation, and amino acid and lipid biosynthesis. Thus, these results seem to suggest that certain collective physiological activities are critical for microbiome-mediated OSCC progression.IMPORTANCE There is growing evidence that changes in the microbiome are associated with carcinogenesis. To date, no consistent oral microbiome composition associated with OSCC has been identified. Longitudinal and functional studies like the study presented here should yield a better understanding of the role that the oral microbiome plays in OSCC. Our findings, obtained using a germ-free mouse model, indicate that the presence of different oral microbiomes enhances tumorigenesis and increases the final number of tumors in mice. By studying community-wide expression profiles, we found that regardless of the phylogenetic composition of the microbiome, the same metabolic activities were consistently associated with OSCC. Therefore, due to the functional redundancy of the microbiome, the critical element in explaining the contribution of the microbiota in OSCC is the collective physiological activity of the community, thus accounting for the previous inability to identify a consensus community profile or etiologic agents for OSCC.

Metabolic property of acetaldehyde production from ethanol and glucose by oral Streptococcus and Neisseria

Acetaldehyde is known to be carcinogenic and produced by oral bacteria. Thus, bacterial acetaldehyde production might contribute to oral cancer. Therefore, we examined bacterial acetaldehyde production from ethanol and glucose under various conditions mimicking the oral cavity and clarified the metabolic pathways responsible for bacterial acetaldehyde production. Streptococcus mitis, S. salivarius, S. mutans, Neisseria mucosa and N. sicca were used. The bacterial metabolism was conducted at pH 5.0–8.0 under aerobic and anaerobic conditions. The production of acetaldehyde and organic acids was measured with gas chromatography and HPLC, respectively. Bacterial enzymes were also assessed. All of the bacteria except for S. mutans exhibited their greatest acetaldehyde production from ethanol at neutral to alkaline pH under aerobic conditions. S. mutans demonstrated the greatest acetaldehyde from glucose under anaerobic conditions, although the level was much lower than that from ethanol. Alcohol dehydrogenase and NADH oxidase were detected in all of the bacteria. This study revealed that oral indigenous bacteria, Streptococcus and Neisseria can produce acetaldehyde, and that such acetaldehyde production is affected by environmental conditions. It was suggested that alcohol dehydrogenase and NADH oxidase are involved in ethanol-derived acetaldehyde production and that the branched-pathway from pyruvate is involved in glucose-derived acetaldehyde production.

Compositional and Functional Analysis of the Microbiome in Tissue and Saliva of Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is affected by the interaction between oral pathogen and holobionts, or the combination of the host and its microbial communities. Studies have indicated the structure and feature of the microbiome in OSCC tissue and saliva, the relationships between microbiota and OSCC sites, stages remain unclear. In the present study, OSCC tissue (T), saliva (S) and mouthwash (W) samples were collected from the same subjects and carried out the microbiome study by 16S sequencing. The results showed the T group was significantly different from the S and W groups with the character of lower richness and diversity. Proteobacteria were most enriched in the T group at the phylum level, while Firmicutes were predominant in groups S and W. At the genus level, the predominant taxa of group T were Acinetobacter and Fusobacterium, and for group S and W, the predominant taxa were Streptococcus and Prevotella. The genera related to late stage tumors were Acinetobacter and Fusobacterium, suggesting microbiota may be implicated in OSCC developing. Both compositional and functional analyses indicated that microbes in tumor tissue were potential indicator for the initiation and development of OSCC.

Culture-independent studies on bacterial dysbiosis in oral and oropharyngeal squamous cell carcinoma: A systematic review

Imbalance within the resident bacterial community (dysbiosis), rather than the presence and activity of a single organism, has been proposed to be associated with, and to influence, the development and progression of various diseases; however, the existence and significance of dysbiosis in oral/oropharyngeal cancer is yet to be clearly established. A systematic search (conducted on 25/01/2018 and updated on 25/05/2018) was performed on three databases (Pubmed, Web of Science & Scopus) to identify studies employing culture-independent methods which investigated the bacterial community in oral/oropharyngeal cancer patients compared to control subjects. Of the 1546 texts screened, only fifteen publications met the pre-determined selection criteria. Data extracted from 731 cases and 809 controls overall, could not identify consistent enrichment of any particular taxon in oral/oropharyngeal cancers, although common taxa could be identified between studies. Six studies reported the enrichment of Fusobacteria in cancer at different taxonomic levels whereas four studies reported an increase in Parvimonas. Changes in microbial diversity remained inconclusive, with four studies showing a higher diversity in controls, three studies showing a higher diversity in tumors and three additional studies showing no difference between tumors and controls. Even though most studies identified a component of dysbiosis in oral/oropharyngeal cancer, methodological and analytical variations prevented a standardized summary, which highlights the necessity for studies of superior quality and magnitude employing standardized methodology and reporting. Indeed an holistic metagenomic approach is likely to be more meaningful, as is understanding of the overall metabolome, rather than a mere enumeration of the organisms present.

Role of Oral Microbiome Signatures in Diagnosis and Prognosis of Oral Cancer

Despite advancement in cancer treatment, oral cancer has a poor prognosis and is often detected at late stage. To overcome these challenges, investigators should search for early diagnostic and prognostic biomarkers. More than 700 bacterial species reside in the oral cavity. The oral microbiome population varies by saliva and different habitats of oral cavity. Tobacco, alcohol, and betel nut, which are causative factors of oral cancer, may alter the oral microbiome composition. Both pathogenic and commensal strains of bacteria have significantly contributed to oral cancer. Numerous bacterial species in the oral cavity are involved in chronic inflammation that lead to development of oral carcinogenesis. Bacterial products and its metabolic by-products may induce permanent genetic alterations in epithelial cells of the host that drive proliferation and/or survival of epithelial cells. Porphyromonas gingivalis and Fusobacterium nucleatum induce production of inflammatory cytokines, cell proliferation, and inhibition of apoptosis, cellular invasion, and migration thorough host cell genomic alterations. Recent advancement in metagenomic technologies may be useful in identifying oral cancer-related microbiome, their genomes, virulence properties, and their interaction with host immunity. It is very important to address which bacterial species is responsible for driving oral carcinogenesis. Alteration in the oral commensal microbial communities have potential application as a diagnostic tool to predict oral squamous cell carcinoma. Clinicians should be aware that the protective properties of the resident microflora are beneficial to define treatment strategies. To develop highly precise and effective therapeutic approaches, identification of specific oral microbiomes may be required. In this review, we narrate the role of microbiome in the progression of oral cancer and its role as an early diagnostic and prognostic biomarker for oral cancer.