Oral microbiota and gastric cancer: recent highlights and knowledge gaps.

Gastric cancer is one of the most common malignant tumors worldwide and has a high mortality rate. However, tests for the early screening and diagnosis of gastric cancer are limited and invasive. Certain oral microorganisms are over-expressed in gastric cancer, but there is heterogeneity among different studies. Notably, each oral ecological niche harbors specific microorganisms. Among them, tongue coating, saliva, and dental plaque are important and unique ecological niches in the oral cavity. The colonization environment in different oral niches may be a source of heterogeneity. In this paper, we systematically discuss the latest developments in the field of the oral microbiota and gastric cancer and elucidate the enrichment of microorganisms in the oral ecological niches of the tongue coatings, saliva, and dental plaque in gastric cancer patients. The various potential mechanisms by which the oral microbiota induces gastric cancer (activation of an excessive inflammatory response; promotion of proliferation, migration, invasion, and metastasis; and secretion of carcinogens, leading to imbalance in gastric microbial communities) are explored. In this paper, we also highlight the applications of the rapeutics targeting the oral microbiota in gastric cancer and suggests future research directions related to the relationship between the oral microbiota and gastric cancer.

Preliminary analysis of mucosal and salivary bacterial communities in oral lichen planus.

OBJECTIVE: To characterize the bacterial community from different oral niches (buccal mucosa and saliva) in oral lichen planus (OLP) patients. SUBJECTS AND METHODS: This preliminary study analyzed site-specific (mucosa and saliva) microbial landscape of 20 OLP patients and 10 healthy controls. RESULTS: The microbial diversity was similar between OLP patients and healthy controls in both salivary and mucosal communities. However, the topological properties of co-occurrence networks of salivary and mucosal microbiome were different between healthy controls and OLP patients. SparCC analysis inferred three and five keystone taxa in the salivary and mucosal microbial networks of healthy controls, respectively. However, in the salivary and mucosal bacterial networks of OLP patients, only one hub OTU and three OTUs were identified as keystone taxa, respectively. In addition, analysis of community cohesion revealed that mucosal microbial community in OLP patients had lower stability than that in healthy controls. In final, correlation assay showed that the clinical severity of OLP was positively associated with the relative abundance of Rothia in saliva but negatively associated with that of Porphyromonas on mucosa. CONCLUSIONS: The salivary and mucosal bacterial communities of OLP patients differ in terms of composition, the genera associated with OLP severity, and co-occurrence patterns.

Characteristics of Microbial Distribution in Different Oral Niches of Oral Squamous Cell Carcinoma.

Oral squamous cell carcinoma (OSCC), one of the most common malignant tumors of the head and neck, is closely associated with the presence of oral microbes. However, the microbiomes of different oral niches in OSCC patients and their association with OSCC have not been adequately characterized. In this study, 305 samples were collected from 65 OSCC patients, including tumor tissue, adjacent normal tissue (paracancerous tissue), cancer surface tissue, anatomically matched contralateral normal mucosa, saliva, and tongue coat. 16S ribosomal DNA (16S rDNA) sequencing was used to compare the microbial composition, distribution, and co-occurrence network of different oral niches. The association between the microbiome and the clinical features of OSCC was also characterized. The oral microbiome of OSCC patients showed a regular ecological distribution. Tumor and paracancerous tissues were more microbially diverse than other oral niches. Cancer surface, contralateral normal mucosa, saliva, and tongue coat showed similar microbial compositions, especially the contralateral normal mucosa and saliva. Periodontitis-associated bacteria of the genera Fusobacterium, Prevotella, Porphyromonas, Campylobacter, and Aggregatibacter, and anaerobic bacteria were enriched in tumor samples. The microbiome was highly correlated with tumor clinicopathological features, with several genera (Lautropia, Asteroleplasma, Parvimonas, Peptostreptococcus, Pyramidobacter, Roseburia, and Propionibacterium) demonstrating a relatively high diagnostic power for OSCC metastasis, potentially providing an indicator for the development of OSCC.

Defining Metaniches in the Oral Cavity According to Their Microbial Composition and Cytokine Profile.

The human oral microbiota consists of over 700 widespread taxa colonizing the oral cavity in several anatomically diverse oral niches. Lately, sequencing of the 16S rRNA genes has become an acknowledged, culture-independent method to characterize the oral microbiota. However, only a small amount of data are available concerning microbial differences between oral niches in periodontal health and disease. In the context of periodontitis, the cytokine expression in the gingival crevicular fluid has been studied in detail, whereas little is known about the cytokine profile in hard and soft tissue biofilms. In order to characterize oral niches in periodontal health, the oral microbiota and cytokine pattern were analyzed at seven different sites (plaque (P), gingival crevicular fluid (GCF), saliva (S), tongue (T), hard palate (HP), cheek (C) and sublingual area (U)) of 20 young adults using next-generation sequencing and multiplex immunoassays. Site-specific microbial compositions were detected, which clustered into three distinct metaniches ("P-GCF", "S-T-HP" and "C-U") and were associated with niche-/metaniche-specific cytokine profiles. Our findings allow the definition of distinct metaniches according to their microbial composition, partly reflected by their cytokine profile, and provide new insights into microenvironmental similarities between anatomical diverse oral niches.

Bacterial viability in oral biofilm after tooth brushing with amine fluoride or sodium fluoride.

OBJECTIVE: The aim of this study was to investigate the effects of sodium fluoride (NaF) and amine fluoride (AmF) on bacterial viability in the oral cavity. MATERIAL AND METHODS: Healthy subjects brushed their teeth with either fluoride free toothpaste, NaF- or AmF-containing toothpaste. Biofilm smears from different locations were collected before and immediately and 30 and 120 min after tooth brushing. The smears were stained with live/dead bacterial staining, and the number of the respective bacteria was counted. The data were statistically analyzed by comparing the numbers of bacteria before and after the application of no fluoride, NaF and AmF. RESULTS: The highest numbers of bacteria were found in the tongue biofilm, followed by the palatal and cheek biofilm. The lowest numbers were found in the mouth floor biofilm. After the application of AmF, no changes in the numbers of bacteria were found in the biofilms, except for the cheek, where they were reduced. After the application of NaF, the number of bacteria decreased significantly in all biofilms. After 120 min, bacterial regrowth was complete. CONCLUSIONS: AmF has only little effect on the bacterial viability of oral biofilms. NaF application reduces the number of living bacteria in the oral biofilms. This effect lasts not longer than 120 min.

What is the influence of tonsillectomy on the level of periodontal pathogens on the tongue dorsum and in periodontal pockets.

BACKGROUND: For periodontal treatment, the full mouth disinfection approach suggests disinfection of oral soft tissues, such as tongue and tonsils concomitant to scaling and root planning since patients might benefit from treatment of these oral niches either. Periodontopathogenes in tonsillar tissue support this hypothesis. This prospective controlled clinical study investigated the change in the oral flora of patients who underwent tonsillectomy. Pockets were tested for eleven bacterial species before and six weeks after the surgical intervention. METHODS: Fifty generally healthy adults were included in this study. The test group consisted of 25 patients with tonsillectomy. The control group included 25 patients with otorhinolarynologic surgery without involvement of the oral cavity. Clinical parameters such as probing pocket depth, bleeding-on-probing index and plaque index were registered the evening before surgery. Also bacterial samples from the gingival sulcus and dorsum linguae were taken, and an additional sample from the removed tonsils in the test group. Six weeks after the intervention microbial samples of pockets and tongue were taken again. Data were tested for significant differences using Wilcoxon rank and Whitney-u-test. RESULTS: No relevant intra- or intergroup differences were found for the change of the eleven investigated species. CONCLUSION: Based on the results of the present study, tonsillectomy does not seem to have an immediate relevant effect on the bacterial flora of tongue or periodontium. This study design was approved by the ethical committee of Zurich (KEK-ZH-Nr.2013-0419). TRIAL REGISTRATION: The trial was retrospectively registered in the German Clinical Trials Register ( DRK00014077 ) on February 20, 2018.

Stem cells from oral niches: a review.

AIM: Stem cell research in recent years have been considered the most advanced sort of medical-scientific research and early results have aroused great expectations. Also in dentistry many studies were performed with the final aim of obtaining new bone and new teeth. In this work we describe the state of the art in dental science stem cell research. METHODS: We have performed a web-based research on MEDLINE within (www.pubmed.gov). We have used "stem cells from human exfoliated deciduous teeth" (24 paper found), "periodontal ligament stem cells" (32 paper found), "stem cell apical papilla" (16 paper found), "dental pulp stem cells" (136 paper found) as keywords for research. For each keyword we have performed a complete review focusing on knowledge upgrade. RESULTS: For each topic was created a selection of papers in chronological order of publication date so to give a timetable of the development of the research for each niche. CONCLUSION: Research about stem cell from oral niches began in 2000 and every year papers publicated were more than the precedent. This review analysed about 180 articles most of which in the last 5 years. Dentla pulp from adult as from deciduous teeth seems to be the most valuable font of stem cells due to the pluripotential type of cells.