Irritable Bowel Syndrome and Oral microbiota

Irritable Bowel Syndrome and Oral microbiota



Irritable bowel syndrome (IBS) is the most commonly diagnosed functional gastrointestinal disorder characterized by chronic abdominal pain and changed bowel habits in the absence of an overtly identifiable cause. 

IBS has gained significant interest in healthcare due to its high occurrence, complex pathophysiology, difficult diagnosis due to a wide range of non-specific symptoms. 

IBS can present with a wide range of both gastrointestinal and extraintestinal symptoms. These include:

(1) chronic abdominal pain with variable intensity and periodic exacerbations; (2) altered bowel habits ranging from diarrhea, constipation, alternating diarrhea and constipation, or normal bowel habits alternating with either diarrhea and/or constipation;

(3) diarrhea characterized by frequent loose stools of small to moderate volume; (4) prolonged constipation with interludes of diarrhea or normal bowel function with often hard, pellet-shaped stools and a sense of incomplete evacuation even when the rectum is empty; (5) extraintestinal symptoms, such as impaired sexual function, dysmenorrhea, dyspareunia, increased urinary frequency and urgency, and fibromyalgia symptoms (Saha L. Irritable bowel syndrome: Pathogenesis, diagnosis, treatment, and evidence-based medicine. World J. Gastroenterol. 2014;20:6759–6773). Diagnosis is based on intestinal syntoms.

Hypersensitivity to certain foods, especially foods that contain high amounts of fructose, plays a role in the pathophysiology.  (Irritable Bowel Syndrome: Clinical Manifestations, Dietary Influences, and Management. Ronald Ikechi et al. Healthcare (Basel). 2017 Jun; 5(2): 21). It is characterized by a decreased in microbial richness (i.e. number of phylotypes in a community) and diversity (i.e., variation in community structure) and differences in the abundance of certain microbes. (The microbiome of the oral mucosa in irritable bowel syndrome. Nicolaas H. Fourie et al. Gut Microbes. 2016 Jul 3;7(4):286-301. Epub 2016 Mar 10).

The prevalence ranges from 10–15% in population-based studies in North America and Europe.

The elevated chronic consumption of high-fructose corn syrup has been linked to various health problems, not only to IBS but also diabetes mellitus, non-alcoholic fatty liver disease, aging and cholesterol.

(Irritable Bowel Syndrome: Clinical Manifestations, Dietary Influences, and Management. Ronald Ikechi et al. Healthcare (Basel). 2017 Jun; 5(2): 21)

Microbiome and IBS.

Oral microbiome, that appears to be stable within an individual over the short- (days) and long term (years), varies less within and between individuals  than the microbiome from other body regions, including the gut.

A comprehensive comparison of microbial communities across different body sites, including the oral cavity and the gut, found that microbial community types of the mouth and the gut were predictive of each other. This association does not suggest that the oral cavity harbors the same bacteria as the colon, but that perturbations in the intestinal or colonic bacterial communities are reflected in oral bacterial communities.

This phenomenon has been further demonstrated in an animal model of colitis. Disease associated perturbations in the oral microbiome could be significant as an indicator or diagnostic of systemic dysbiosis and/or specific pathological conditions or risks. Oral health and variation in the oral microbiome has been associated with several disease conditions, including IBS. Oral microbial perturbations and microbial variation in relations to symptom severity remain largely unexplored.

It remains unclear how the oral microbiota may affect systemic and/or non-oral biology and pathology. Oral microbes are capable of producing toxic and mutagenic metabolites (e.g., alcohol to acetaldehyde) to which the oral and gastrointestinal (GI) tract is exposed. Oral bacteria can colonize distant (GI) sites, or translocate across the epithelial barrier to colonize and infect non-oral systems or organs (e.g. joints and heart). Microbes could also directly modulate host inflammatory and cell signaling pathways as a ligand source.

Patients affected by IBS follow a strict elimination diet that probably also determine changes in gut microbiota with health implications

(Food components and irritable bowel syndrome. Gibson PR, Varney J, Malakar S, Muir JG. Gastroenterology. 2015 May; 148(6):1158-74.e4.)

We don't know yet if oral microbiological changes are caused by intestinal bacterial modification or it depends on external factors like diet modification and/or socioeconomical factors that determine a less oral hygiene. Interpretation of the oral microbiome, as with the gut microbiome, is complicated by a range of anthropogenic confounders (e.g. socio-economic and culturally mediated dietary or hygiene preferences etc.) 

A growing body of research indicates that the oral cavity is a potential source of microbiome information relevant to non-oral conditions. Oral substrates may be a useful minimally invasive source of informations with diagnostic potential. The intra-oral DNA sampling is effected through Buccal swabs. DNA is extracted from Buccal cells and mucus (The microbiome of the oral mucosa in irritable bowel syndrome. Nicolaas H. Fourie et al. Gut Microbes. 2016 Jul 3;7(4):286-301)

Some bacteria in the oral cavity have recently been investigated for their association with IBS (Yoneda et al., 2016). These bacteria can be analyzed as microbial biomarkers. (Ismail et al., 2012; Swidsinski et al., 2009). The dominant genera, Veillonella and Haemophilus, were recommended to largely contribute to dysbiosis of salivary microbiota in IBS patients (Said et al., 2014). Reguarding species evaluation, C. concisus (Ismail et al., 2012; Mahendran et al., 2013) and Mycobacterium avium Paratuberculosis (Bruno and Isabelle, 2015) have been investigated for its role in saliva related dysbiosis in IBS. In a recent review, two frequently used sampling origins are primarily discussed: saliva and subgingival plaques. Sampling Strategies for Three-Dimensional Spatial Community Structures in IBD Microbiota Research (Shaocun Zhang et al).

Further research on the oral microbiota might hold potential clinical and diagnostic utility in the future (Docktor et al., 2012).