Role Of Oral Microbiota Research Articles

Role of Oral Microbiota in Preserving Health and Disease Management

Role of Oral Microbiota in Preserving Health and Disease Management

The role of oral microbiota in the development of oral mucositis in pediatric oncology patients treated with antineoplastic drugs: a systematic review

BackgroundIn the pediatric oncology population, oral mucositis as a consequence of chemotherapy is a highly prevalent complication which strongly affects both the quality of life and treatment possibilities of the patients. Still, the etiopathological mechanisms carrying to its development are not fully understood, although a possible role of oral dysbiosis has been previously investigated with unclear conclusions. The aim of this systematic review was to assess the available evidence on the role of microbiota in the development of oral mucositis.MethodsA systematic literature search was performed following PRISMA guidelines. Three electronic databases were searched up until April 2023 and a following manual search included the reference lists of the included studies and reviews. Studies reporting microbiological and clinical data of pediatric patients treated by antineoplastic drugs were included.ResultsThirteen studies met the inclusion criteria, reporting an average mucositis prevalence of 57,6%. Candida albicans infections were frequently observed in studies performing microbiological analysis on oral lesions, in contrast with the low rate detection of the Herpes simplex viruses. Bacterial species such as coagulase-negative Staphylococci and Streptococcus viridans were detected more frequently on lesion sites. Studies reporting a quantitative analysis of the general flora did not show comparable results. Risk of bias assessment among studies was generally considered high or very high.ConclusionsWhile the specific role of certain microbiological agents, such as Candida albicans, was frequently reported among studies, data regarding the general dynamics of oral microbiota in the development of oral mucositis are lacking in the current literature. Thus, more studies are needed to provide the knowledge required in order to improve protocols for the prevention and treatment of this threatening complication.

Salivary signatures of oral-brain communication in sleep bruxers.

Microbiota and their interaction with hosts have been of great interest in brain research in recent years. However, the role of oral microbiota in mental illness and the underlying mechanism of oral-brain communication remains elusive. Sleep bruxism (SB) is an oral parafunctional activity related to the nervous system and is considered a risk factor for harmful clinical consequences and severe systemic conditions. Exploring the connection between oral microbiota and sleep bruxism may deepen our understanding of the complex relationship between oral-brain axis and provide insights for treatment. In this study, salivary samples were collected from 22 individuals with SB and 21 healthy controls, and metagenomics with metabolomics was performed. Nonparametric Wilcoxon test were applied for the statistical analysis between the two groups. Microbial dysbiosis and altered oral metabolites were found in the SB individuals. The characteristic metabolite N-acetylglucosamine (GlcNAc) (VIP=8.4823, P<0.05) was correlated to a statistically lower Streptococcus mitis level in SB individuals. Salivary IFN-g level and IFN-g/IL-4 ratio were detected with significant changes in a chip assay. Amino acid metabolism pathways were upregulated, and the pathway with the largest number of differentially expressed genes is related to amino-tRNA charging pathway, while the most significantly enriched pathway is related to arginine biosynthesis. Neurotransmitter-associated pathways with glutamatergic and GABAergic synapses and cardiovascular system-related pathways were enriched in the SB group. These results indicate a possible neuroimmune regulatory network of oral-brain communication in SB, which helps explain the mechanism of the oral microbiome with the host in sleep bruxers and provides a reference for early clinical and therapeutic intervention to improve the diagnosis and treatment of SB and similar diseases.

Commensal Oral Microbiota, Disease Severity, and Mortality in Fibrotic Lung Disease.

Rationale: Oral microbiota associate with diseases of the mouth and serve as a source of lung microbiota. However, the role of oral microbiota in lung disease is unknown. Objectives: To determine associations between oral microbiota and disease severity and death in idiopathic pulmonary fibrosis (IPF). Methods: We analyzed 16S rRNA gene and shotgun metagenomic sequencing data of buccal swabs from 511 patients with IPF in the multicenter CleanUP-IPF (Study of Clinical Efficacy of Antimicrobial Therapy Strategy Using Pragmatic Design in IPF) trial. Buccal swabs were collected from usual care and antimicrobial cohorts. Microbiome data were correlated with measures of disease severity using principal component analysis and linear regression models. Associations between the buccal microbiome and mortality were determined using Cox additive models, Kaplan-Meier analysis, and Cox proportional hazards models. Measurements and Main Results: Greater buccal microbial diversity associated with lower FVC at baseline (mean difference, -3.60; 95% confidence interval [CI], -5.92 to -1.29% predicted FVC per 1-unit increment). The buccal proportion of Streptococcus correlated positively with FVC (mean difference, 0.80; 95% CI, 0.16 to 1.43% predicted per 10% increase) (n = 490). Greater microbial diversity was associated with an increased risk of death (hazard ratio, 1.73; 95% CI, 1.03-2.90), whereas a greater proportion of Streptococcus was associated with a reduced risk of death (HR, 0.85; 95% CI, 0.73 to 0.99). The Streptococcus genus was mainly composed of Streptococcus mitis species. Conclusions: Increasing buccal microbial diversity predicts disease severity and death in IPF. The oral commensal S. mitis spp associates with preserved lung function and improved survival.

Oral Microbiome and Multiple Sclerosis? A Novel Concept!

Human oral microbiota refers to the significant number of microorganisms that exist in the human mouth. It is one of the most intricate microbial populations in the human body. Recent studies have suggested the role of the oral microbiome in diverse nervous system diseases. Consequently, investigating the impact of the oral microbiome in patients with Multiple Sclerosis (MS) could reveal potential associations with the disease. In this review, the role of oral microbiota in MS patients has been addressed. The findings of this study hold promise for future approaches to oral and dental health in patients with Multiple Sclerosis. Also, In the future, oral microbiota may become a new target for uncovering novel approaches to prevent and/or treat MS.

Role of oral microbiota in Alzheimers disease: A systematic review of clinical studies

Alzheimers disease (AD) is one of the most common neurodegenerative diseases in the world, causing dementia among the elderly. Oral microbiome may be associated with AD. This systematic review summarizes the current role of the oral microbiome in the etiology and diagnosis of AD. Articles included were sourced primarily from electronic databases including PubMed, EMBASE, Web of Science, Scopus, and Cochrane Library from January 2011 to August 2022 and in OpenGrey and Google Scholar for grey literature. Relevant studies were selected using a two-stage approach involving the screening of titles and abstracts and full-text evaluation by two authors. Risk of bias was also performed using the Newcastle Ottawa scale (NOS) before qualitative synthesis. 18 studies out of 1079 citations were included in this review. The median NOS rating (IQR) of the reviewed studies was 8 (7.25 9). Most studies suggested that there was an association between oral microbiome and AD. Some claimed that oral microbiome might be the risk factor of AD using disparate approaches. Others also detected antibodies to oral microorganisms among AD patients and observed a significantly different alpha diversity among patients with AD than controls. Although limited by the number of studies, this review found that a change in the oral microbiome may be indicative of AD severity. Oral microbiome may be associated with Alzheimers disease. Some microbial species may be risk factors or aid diagnosis for AD, however more research is still needed to establish their role in AD etiology and noninvasive diagnosis.

The role of oral microbiota in cancer.

Cancer remains a significant global challenge, with an estimated 47% increase in cancer patients from 2020 to 2040. Increasing research has identified microorganism as a risk factor for cancer development. The oral cavity, second only to the colon, harbors more than 700 bacterial species and serves as a crucial microbial habitat. Although numerous epidemiological studies have reported associations between oral microorganisms and major systemic tumors, the relationship between oral microorganisms and cancers remains largely unclear. Current research primarily focuses on respiratory and digestive system tumors due to their anatomical proximity to the oral cavity. The relevant mechanism research mainly involves 47% dominant oral microbial population that can be cultured in vitro. However, further exploration is necessary to elucidate the mechanisms underlying the association between oral microbiota and tumors. This review systematically summarizes the reported correlations between oral microbiota and common cancers while also outlining potential mechanisms that may guide biological tumor treatment.

The Role of Dysbiotic Oral Microbiota in Cardiometabolic Diseases: A Narrative Review.

Over the past decade, there have been significant advancements in the high-flow analysis of "omics," shedding light on the relationship between the microbiota and the host. However, the full recognition of this relationship and its implications in cardiometabolic diseases are still underway, despite advancements in understanding the pathophysiology of these conditions. Cardiometabolic diseases, which include a range of conditions from insulin resistance to cardiovascular disease and type 2 diabetes, continue to be the leading cause of mortality worldwide, with a persistently high morbidity rate. While the link between the intestinal microbiota and cardiometabolic risks has been extensively explored, the role of the oral microbiota, the second-largest microbiota in the human body, and specifically the dysbiosis of this microbiota in causing these complications, remains incompletely defined. This review aims to examine the association between the oral microbiota and cardiometabolic diseases, focusing on the dysbiosis of the oral microbiota, particularly in periodontal disease. Additionally, we will dive into the mechanistic aspects of this dysbiosis that contribute to the development of these complications. Finally, we will discuss potential prevention and treatment strategies, including the use of prebiotics, probiotics, and other interventions.

Role of oral microbiota in irreversible pulpitis - Current strategies and future perspectives.

Irreversible pulpitis is an inflammation of the tooth pulp caused by an opportunity-driven invasion of the pulp space by oral microbiota typically prevalent in the oral cavity. Microbial organisms are extensively recognised to be the fundamental cause of endodontic infections and treatment failures. Previously, bacterial species responsible for these infections were largely recognised using conventional microbial culture techniques, lending credence to the widely held belief that anaerobic Gram-negative bacteria frequently enter the pulp space and trigger endodontic infections. The advent of novel technologies grants the advantage of detecting and studying microbial populations via an amalgamation of the modern "Omics" techniques and meticulous bioinformatics analysis, additionally detecting the metatranscriptome, metaproteome and metabolome along with the metagenome. Amongst these analytical strategies, metagenomic analyses are essentially pragmatic for investigating the oral microbiome. Metagenomics favor not only assessment of microbial composition in diseased conditions, but also contributes to detection of novel, potentially pathogenic species inclusive of non-viable bacteria. The present review describes current knowledge of root canal microbiome, including its composition and functional attributes, the novel strategies available for detection of microbiome as well as challenges associated and provides some crucial pointers for areas of future research.

Role of Helicobacter pylori in Gastric Carcinoma: A Review.

Gastric cancer (GC) is one of the leading causes of cancer-related deaths globally. Gastritis caused byHelicobacter pylori (H. pylori)is a potent cause of gastrointestinal malignancies. The majority of all humans on the planet haveH. pylori invasionin their stomachs, yet only a few diseased people develop GC. The human gastrointestinal system contains a broad population of microorganisms in addition toH. pylori.H. pyloriheterogeneity has been studied because not allH. pyloridiseases result in cancer. Individuals in the adult age group account for the bulk of gastric carcinoma cases.H. pylorihas various strains, which is beneficial for its survival in host cell epithelium for a longer duration of time. Along withH. pylori, oral microbes have a major role in the pathogenicity of gastric carcinoma. The complex ecology of oral microbiota helps to defend against infections, preserve homeostasis, and regulate the immune system. In contrast, oral microbiota is involved in various mechanisms like anti-apoptotic activity, suppression of the immune system of the host, and initiation of chronic inflammation. These oral microbes are also responsible for the development of mutations. Interactions between the host immune system and bacteria promote the progression of cancer. For this review, various research articles were studied, and information was collected using databases like PubMed and Google Scholar. This review emphasizes on the role ofH. pyloriin gastric carcinoma, its pathogenesis,the role of various virulence factors and risk factors related to it, the role of oral microbiota in gastric carcinoma pathogenesis, diagnostic modalities, treatment options, and preventive measures for gastric carcinoma.

Oral Microbiota Profile in Patients with Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis.

Microbiota has been associated with autoimmune diseases, with nasal Staphylococcus aureus being implicated in the pathogenesis of anti-neutrophil cytoplasmic antibody–associated vasculitis (AAV). Little is known about the role of oral microbiota in AAV. In this study, levels of IgG antibodies to 53 oral bacterial species/subspecies were screened using immunoblotting in plasma/serum in pre-symptomatic AAV-individuals (n = 85), matched controls, and established AAV-patients (n = 78). Saliva microbiota from acute-AAV and controls was sequenced from 16s rDNA amplicons. Information on dental status was extracted from a national register. IgG levels against oral bacteria were lower in established AAV versus pre-AAV and controls. Specifically, pre-AAV samples had, compared to controls, a higher abundance of periodontitis-associated species paralleling more signs of periodontitis in established AAV-patients than controls. Saliva microbiota in acute-AAV showed higher within-sample diversity but fewer detectable amplicon-sequence variants and taxa in their core microbiota than controls. Acute-AAV was not associated with increased abundance of periodontal bacteria but species in, e.g., Arthrospira, Staphylococcus, Lactobacillus, and Scardovia. In conclusion, the IgG profiles against oral bacteria differed between pre-AAV, established AAV, and controls, and microbiota profiles between acute AAV and controls. The IgG shift from a pre-symptomatic stage to established disease cooccurred with treatment of immunosuppression and/or antibiotics.

Role of Oral Microbiota in Carcinogenesis: A Short Review.

A strong and healthy microbiome is responsible for homeostasis between the host and microbiota which is necessary to achieve the normal functioning of the body. Dysbiosis provokes prevalence of pathogenic microbes, leading to alterations in gene expression profiles and metabolic processes. This in turn results in anomalous immune responses of the host. Dysbiosis may be associated with a wide variety of diseases like irritable bowel syndrome, coeliac disease, allergic conditions, bronchitis, asthma, heart diseases and oncogenesis. Presently, the links between oral microbial consortia and their functions, not only in the preservation of homeostasis but also pathogenesis of several malignancies have gained much awareness from the scientific community. The primary intent of this review is to highlight the dynamic role of oral microbiome in oncogenesis and its progression through various mechanisms. A literature search was conducted using multiple databases comprising of PubMed, Scopus, Google Scholar, and Cochrane electronic databases with keywords including microbiome, microbiota, carcinogenesis, tumorigenesis, and immunosuppression. Current and the past literature has pointed out the role of microorganisms in oncogenesis. It may be put forth that both the commensal and pathogenic strains of oral microbiome play an undeniably conspicuous role in carcinogenesis at different body sites.

Alterations of oral microbiota in Chinese children with viral encephalitis and/or viral meningitis.

The role of oral microbiota in viral encephalitis and/or viral meningitis (VEVM) remains unclear. In this hospital-based, frequency-matched study, children with clinically diagnosed VEVM (n = 68) and those with other diseases (controls, n = 68) were recruited. Their oral swab samples were collected and the oral microbiota was profiled using 16S rRNA gene sequencing. The oral microbiota of children with VEVM exhibited different beta diversity metrics (unweighted UniFrac distance: P < 0.001, R2 = 0.025, Bray-curtis dissimilarity: P = 0.045, R2 = 0.011, and Jaccard dissimilarity: P < 0.001, R2 = 0.017) and higher relative abundances of taxa identified by Linear discriminant analysis (LDA) with effect size (Enterococcus, Pedobacter, Massilia, Prevotella_9, Psychrobacter, Butyricimonas, Bradyrhizobium, etc., LDA scores > 2.0) when compared with the control group. The higher pathway abundance of steroid hormone biosynthesis predicted by oral microbiota was suggested to be linked to VEVM (q = 0.020). Further, a model based on oral microbial traits showed good predictive performance for VEVM with an area under the receiver operating characteristic curve of 0.920 (95% confidence interval: 0.834–1.000). Similar results were also obtained between children with etiologically diagnosed VEVM (n = 43) and controls (n = 68). Our preliminary study identified VEVM-specific oral microbial traits among children, which can be effective in the diagnosis of VEVM.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s12275-022-1560-y.

Oral Osteomicrobiology: The Role of Oral Microbiota in Alveolar Bone Homeostasis.

Osteomicrobiology is a new research field in which the aim is to explore the role of microbiota in bone homeostasis. The alveolar bone is that part of the maxilla and mandible that supports the teeth. It is now evident that naturally occurring alveolar bone loss is considerably stunted in germ-free mice compared with specific-pathogen-free mice. Recently, the roles of oral microbiota in modulating host defense systems and alveolar bone homeostasis have attracted increasing attention. Moreover, the mechanistic understanding of oral microbiota in mediating alveolar bone remodeling processes is undergoing rapid progress due to the advancement in technology. In this review, to provide insight into the role of oral microbiota in alveolar bone homeostasis, we introduced the term “oral osteomicrobiology.” We discussed regulation of alveolar bone development and bone loss by oral microbiota under physiological and pathological conditions. We also focused on the signaling pathways involved in oral osteomicrobiology and discussed the bridging role of osteoimmunity and influencing factors in this process. Finally, the critical techniques for osteomicrobiological investigations were introduced.

Periodontitis as a Risk Factor for Breast Cancer - What We Know Till Date?

A healthy microbiome is important for human health because it exhibits a variety of functions in the human body wherein the microbiome dysbiosis can lead to a variety of diseases, including cancer. Recent advances in technology and cost reduction of sequencing have made it possible and much easier for researchers to investigate the role of the microbiome in carcinogenesis. Furthermore, modulation of microflora may serve as an effective adjunct to conventional anticancer therapy that is very important to improve the patient's quality of life. Additionally, microbiome biomarkers can also be used as a diagnostic tool for cancer. So far the association between oral microbial consortia and their interactions with the host in maintaining the human health and the pathogenesis of multiple cancers has gained much popularity in the scientific research community. While the interactions of oral microflora are better established in cancer- like gastric cancer, it is far less understood in others like breast cancer. Therefore, this review briefly outlines the current information on the role of oral microbiota in breast cancer with emphasis on the mechanisms of oral microflora induced carcinogenesis and discusses the emerging role of periodontitis as a risk factor for breast cancer. Clinical relevance; Periodontitis is a very common disease that is characterized by chronic polymicrobial infection and inflammation of gingiva. It might be associated as a risk factor for breast cancer. If this association is validated in large cohort studies, it would serve as a non-invasive biomarker for breast cancer.

Infective Endocarditis: A Focus on Oral Microbiota.

Infective endocarditis (IE) is an inflammatory disease usually caused by bacteria entering the bloodstream and settling in the heart lining valves or blood vessels. Despite modern antimicrobial and surgical treatments, IE continues to cause substantial morbidity and mortality. Thus, primary prevention and enhanced diagnosis remain the most important strategies to fight this disease. In this regard, it is worth noting that for over 50 years, oral microbiota has been considered one of the significant risk factors for IE. Indeed, among the disparate recommendations from the American heart association and the European Society of Cardiology, there are good oral hygiene and prophylaxis for high-risk patients undergoing dental procedures. Thus, significant interest has grown in the role of oral microbiota and it continues to be a subject of research interest, especially if we consider that antimicrobial treatments can generate drug-resistant mutant bacteria, becoming a severe social problem. This review will describe the current knowledge about the relationship between oral microbiota, dental procedures, and IE. Further, it will discuss current methods used to prevent IE cases that originate from oral pathogens and how these should be focused on improving oral hygiene, which remains the significant persuasible way to prevent bacteremia and systemic disorders.

Multiple Brain Abscesses of Odontogenic Origin. May Oral Microbiota Affect Their Development? A Review of the Current Literature

In the last few years, the role of oral microbiota in the setting of oral diseases such as caries, periodontal disease, oral cancer and systemic infections, including rheumatoid arthritis, cardiovascular disease and brain abscess (BA), has attracted the attention of physicians and researchers. Approximately 5–7% of all BAs have an odontogenic origin, representing an important pathological systemic condition with a high morbidity and mortality. A systematic search of two databases (Pubmed and Ovid EMBASE) was performed for studies published up to 5 January 2021, reporting multiple BAs attributed to an odontogenic origin. According to PRISMA guidelines, we included a total of 16 papers reporting multiple BAs due to odontogenic infections. The aim of this review is to investigate the treatment modality and the clinical outcome of patients with multiple BAs due to odontogenic infections, as well as to identify the most common pathogens involved in this pathological status and their role, in the oral microbiota, in the onset of oral infections. A multidisciplinary approach is essential in the management of multiple BAs. Further studies are required to understand better the role of microbiota in the development of multiple BAs.

Neoadjuvant immunotherapy in resectable head and neck cancer: oral cavity carcinoma as a potential research model.

Squamous cell carcinoma of oral cavity (OCSCC) accounts for approximately 25% of cases of head and neck squamous cell carcinoma (HNSCC). Tobacco and alcohol consumption are the main risk factors for both cancers. Surgical resection, combined with adjuvant radiotherapy or radiochemotherapy in patients with high risk of relapse, is the key element in management in the initial stages. However, despite the availability of aggressive multidisciplinary treatments, advanced resectable OCSCC carries poor prognosis; only half of the patients are disease-free 5 years after the surgery. Immunotherapy based on the use of immune checkpoint inhibitors has been proven to be effective in a wide variety of tumours, including recurrent and metastatic HNSCC. These positive results resulted in investigations into its effectiveness in earlier stages of the disease with OCSCC emerging as an interesting research model because of the accessible location of the tumours. This article reviews the potential advantages of emerging immunotherapeutic agents [mainly monoclonal antibodies against programmed cell death-1 (PD-1) immune checkpoint inhibitors] as neoadjuvant treatment for OCSCC at locoregional stages as well as the ongoing clinical trials, challenges in evaluating tumour response, and possible predictive biomarkers of response with highlights regarding the role of oral microbiota as modulators of immune response. The efficacy and safety of anti-PD-1 drugs in these patients have been proven in preliminary trials. If there is a decrease in the relapse rate and an improvement in the overall survival after surgical resection in ongoing trials, preoperative immunotherapy may be established as a treatment option for patients with early stages of the disease.

The Intersection between Oral Microbiota, Host Gene Methylation and Patient Outcomes in Head and Neck Squamous Cell Carcinoma.

Simple SummaryRecently, there has been increased recognition of an association between the bacterial microbiome and cancer. In this study, we characterized the non-HPV head and neck squamous cell carcinoma (HNSCC) microbiome. We found a significant enrichment of Fusobacterium, depletion of Streptococcus, and the microbial signatures of twelve bacterial genera distinguishing HNSCC. With increased Fusobacterium—in particular, F. nucleatum—in our HNSCC cohort and its known association with prognosis in colorectal cancers (CRC), we sought to further characterize the association between clinical outcomes and F. nucleatum, and the host interaction with F. nucleatum. We identified a higher abundance of F. nucleatum in non-smokers and an improved survival, in contrast to CRC. An integrative analysis also identified that the enrichment of F. nucleatum was associated with host gene promoter methylation, suggesting that the bacterial mircobiome status may have a potential role as a prognostic biomarker and be involved in the pathogenesis of HNSCC.The role of oral microbiota in head and neck squamous cell carcinoma (HNSCC) is poorly understood. Here we sought to evaluate the association of the bacterial microbiome with host gene methylation and patient outcomes, and to explore its potential as a biomarker for early detection or intervention. Here we performed 16S rRNA gene amplicon sequencing in sixty-eight HNSCC patients across both tissue and oral rinse samples to identify oral bacteria with differential abundance between HNSCC and controls. A subset of thirty-one pairs of HNSCC tumor tissues and the adjacent normal tissues were characterized for host gene methylation profile using bisulfite capture sequencing. We observed significant enrichments of Fusobacterium and Peptostreptococcus in HNSCC tumor tissues when compared to the adjacent normal tissues, and in HNSCC oral rinses when compared to healthy subjects, while ten other bacterial genera were largely depleted. These HNSCC-related bacteria were discriminative for HNSCC and controls with area under the receiver operating curves (AUCs) of 0.84 and 0.86 in tissue and oral rinse samples, respectively. Moreover, Fusobacterium nucleatum abundance in HNSCC cases was strongly associated with non-smokers, lower tumor stage, lower rate of recurrence, and improved disease-specific survival. An integrative analysis identified that enrichment of F. nucleatum was associated with host gene promoter methylation, including hypermethylation of tumor suppressor genes LXN and SMARCA2, for which gene expressions were downregulated in the HNSCC cohort from The Cancer Genome Atlas. In conclusion, we identified a taxonomically defined microbial consortium associated with HNSCC that may have clinical potential regarding biomarkers for early detection or intervention. Host–microbe interactions between F. nucleatum enrichment and clinical outcomes or host gene methylation imply a potential role of F. nucleatum as a pro-inflammatory driver in initiating HNSCC without traditional risk factors, which warrants further investigation for the underlying mechanisms.

The Role of Oral Microbiota in Intra-Oral Halitosis.

Halitosis is a common ailment concerning 15% to 60% of the human population. Halitosis can be divided into extra-oral halitosis (EOH) and intra-oral halitosis (IOH). The IOH is formed by volatile compounds, which are produced mainly by anaerobic bacteria. To these odorous substances belong volatile sulfur compounds (VSCs), aromatic compounds, amines, short-chain fatty or organic acids, alcohols, aliphatic compounds, aldehydes, and ketones. The most important VSCs are hydrogen sulfide, dimethyl sulfide, dimethyl disulfide, and methyl mercaptan. VSCs can be toxic for human cells even at low concentrations. The oral bacteria most related to halitosis are Actinomyces spp., Bacteroides spp., Dialister spp., Eubacterium spp., Fusobacterium spp., Leptotrichia spp., Peptostreptococcus spp., Porphyromonas spp., Prevotella spp., Selenomonas spp., Solobacterium spp., Tannerella forsythia, and Veillonella spp. Most bacteria that cause halitosis are responsible for periodontitis, but they can also affect the development of oral and digestive tract cancers. Malodorous agents responsible for carcinogenesis are hydrogen sulfide and acetaldehyde.