From Mouth to Gut: Microbial Relationships and Human Health

From MicrobeWiki, the student-edited microbiology resource
Jump to navigationJump to search

Introduction

By Olivia Gumz

With billions of bacteria and microorganisms occupying different areas throughout the human body, the microbiome is a highly complex environment. The oral cavity and the gastrointestinal (GI) tract contain two of the most diverse and inhabited microbial populations[1] [2]. Historically, the research examines both of these areas separately, but more recent data shows that the gut and mouth microbiome have a complex interrelationship now known as the oral gut microbiome axis[3] [4].

Error creating thumbnail: Unable to save thumbnail to destination
This electron microscopy image depicts Fusobacterium nucleatum (F. nucleatum). Photo credit: [1]

This axis brings up many new possibilities for prevention, diagnosis, and therapy and has many implications for comprehending the underlying causes and mechanisms for many gastrointestinal disorders [5] [6] [7]. As the entrance to the digestive tract, the oral cavity is constantly exposed to outside stimuli like food, air, and viruses. Oral microorganisms are transported into the GI tract via saliva, which is produced in significant quantities every day [8]. A growing body of research indicates that many bacteria, including Fusobacterium nucleatum, Porphyromonas gingivilas, and Prevotella, all withstand gastric movement and colonize the gut, particularly in antibiotic disruption. Previously, it was thought that the acidic gastric environment neutralized the majority of these microbes [9] [10] [2] [11]. By encouraging chronic inflammation, changing the integrity of the epithelial barrier, and influencing host immunological responses, these bacteria might be involved in GI diseases [12] [13]. Its pathogenic potential has been highlighted by studies that have connected oral microbiome dysbiosis to the development of gastrointestinal cancers and the worsening of IBD [14] [4] [15]. Given that changes in the mouth microbiota frequently precede or reflect dysbiosis in the gut, the oral gut axis provides encouraging information for non-invasive diagnostic methods [16] [8]. Importantly, this microbiome axis reflects wider inequalities in access to nutrition, dental care, and sanitation—all of which affect microbial balance and the risk of system disease—and so intersects with public health [17] [18] [19]. In underprivileged communities, where oral disorders are common and often go untreated, these concerns are especially pertinent [20]. The principles of microbial transmission through the oral-gut axis, the role translocated bacteria play in the development of GI diseases, public health issues, and potential avenues for clinical study and treatment—including therapies that target the microbiome—are all covered on this wiki page.

The Oral-Gut Microbiome Axis

The mouth cavity and gastrointestinal system are linked through what we call the oral-gut microbial axis, although both areas are physically sectioned from each other. This axis depicts a dynamic microbial continuum that connects systemic gastrointestinal function and mouth health. The ongoing movement of microbes from the mouth to the gut, which is influenced by a number of environmental, behavioral, and physiological factors, is essential to this relationship [8] [3].

Error creating thumbnail: File missing
This image depicts the role of oral microbiomes in gut disease . Photo credit: [[13]]

Microbial Transfer Mechanisms

Adults consume around 500 to 1,500 milliliters of saliva every day, with each milliliter containing roughly 10⁸ bacterial cells. This process aids in the passive movement of oral microorganisms into the intestines [8] [11]. Although gastric acidity was typically thought to eliminate these bacteria, many endure during transit—particularly when pH increases due to medications (e.g., proton pump inhibitors), health conditions, or age-related alterations [20] [2]. Furthermore, periodontal disease and poor oral hygiene raise the microbial burden and encourage biofilms to separate from mucosal and dental surfaces. These dislodged clusters may seed or disturb the local microbiome in the gut after passing through the esophagus undamaged [16] [4]. Inflammation of the oral cavity also increases microbial permeability and encourages the spread of bacteria and corresponding metabolites throughout the body [13].

Similar Microbial Taxa in the Gut and Oral Niches

Several species are common to both the gut and the oral cavity, despite the fact that all microbiomes’ have site-specific characteristics. These include Fusobacterium nucleatum, Veilonella, Streptococcus, and Prevotella [2] [19]. These taxa’s persistence in both settings point to either an active oral-to-gut migration or a shared ancestor. A harmful migratory hypothesis showed that higher concentrations of Porphyromonas gingivalis and oral Fusobacterium nucleatum are associated with increasing presence in colorectal tissue [14]. The fecal and salivary microbiomes of individuals with inflammatory bowel disease (IBD) exhibit overlapping signatures, such as increased Fusobacterium nucleatum and Prevotella, which suggests that microbial compartmentalization is disrupted [9] [5].

Axis-Influencing Factors

The integrity and influence with the oral-gut microbiome axis are modulated by a number of internal and environmental variables. Nutrition is important; diets that are poor in fiber and rich in fat can promote the growth of pathobionts while decreasing beneficial contaminants [15]. By decreasing colonization resistance, antibiotic use reduces microbial diversity and enhances oral-gut transmission [1] [17]. Systemic inflammation and chronic stress can also change mucosal immune reactions and enhance microbial permeability [21] [13].

Oral Bacteria in Conditions of Gut Disease

Fusobacterium nucleatum is arguably the best-known instance of an oral-gut microbial crossover. This species was once thought to be a harmless oral commensal, but it has since been linked to colorectal carcinogenesis, where it alters immune evasion and tumor microenvironments [14] [6]. Gut biopsies from individuals with IBD and liver illness have also revealed the presence of Porphyromonas gingivalis and Prevotella, which are frequently detected in periodontitis [9] [4].

GI Diseases Linked to Oral Microbiota

Error creating thumbnail: File missing
This image displays the many species of microbes seen in a healthy gut and in IBD . Photo credit: [[9]]

Inflammatory Bowel Disease (IBD)

IBD, or inflammatory bowel disease, consists of two chronic conditions: Ulcerative colitis and Crohn’s disease. There have been many recent experiments emphasizing the role oral microorganisms play, but it has been linked in the past to gut dysbiosis and gene susceptibility. In their fecal samples, patients with IBD frequently show higher concentrations of oral-origin bacteria such as Veillonella, Camplylobacter concisus, and Fusobacterium nucleatum [9] [12]. By compromising intestinal epithelial strength and triggering pro-inflammatory immune pathways, these microorganisms mechanistically contribute to IBD. For example, Fusobacterium nucleatum can activate TLR4-mediated NF-kB signaling, which results in the synthesis of cytokines that are essential to the pathophysiology of IBD, including TNF-⍺ and IL-6 [12] [7]. Furthermore, a reciprocal association between intestinal flares and oral inflammation is suggested by the changed salivary microbiomes in IBD patients [16] [20]. According to a number of studies, periodontal disease or poor dental hygiene may make IBD exacerbations more common by promoting oral-to-gut microbial translocation, particularly in people with compromised intestinal or stomach barriers [4] [13]. The significance of dental hygiene as a potential modifiable risk factor for IBD management is highlighted by this mounting research.

Error creating thumbnail: File missing
This table shows the bacteria within the oral-gut microbiome axis for colon diseases . Photo credit: [[6]]


Colorectal Cancer

The high concentration of oral microbes in tumor tissues has made colorectal cancer a focus of study on the mouth-gut microbiome. Specifically, Fusobacterium nucleatum has been found in colorectal cancers on multiple occasions and has been associated with poorer clinical results [14] [6]. A wider oral-gut microbial axis may be at work, as evidenced by the detection of additional oral bacteria in cancerous colon tissues, including P.gingivalis and Treponema dentocola [10]. These bacteria affect carcinogenesis through a variety of methods. By binding to E-cadherin and activating β-catenin signaling, Fusobacterium nucleatum's FadA adhesin attaches to and enters colonic epithelial cells, increasing tumor formation and cell proliferation [12]. By attracting immune cells that infiltrate tumors and preventing T-cell mediated immune responses, it also alters the tumor microenvironment, allowing cancer cells to evade immune detection [3]. It’s interesting to note that mouth and stomach dysbiosis frequently coexist in CRC (colorectal cancer) patients, indicating that the disease process may start up within the digestive tract [5] [8]. These results emphasize how oral microbiota profiles may be used as non-invasive indicators for the prognosis and screening of colorectal cancer.

Liver Disease (Cirrhosis and NAFLD)

Because the liver receives a large amount of blood flow from the stomach through the portal vein, it is especially susceptible to microbial products produced from the gut. The liver can become inflamed by oral bacteria that move to the gut, particularly in cases of dysbiosis or a leaky gut. Cirrhosis and non-alcoholic fatty liver disease (NAFLD) are two conditions where this phenomenon is relevant [22] [23]. According to studies, patients with liver illness had higher levels of Fusobacterium nucleatum and P. gingivalis in their feces, which suggests that oral-gut microbial traffic plays a role in hepatic pathology [5] [13]. By activating Kupffer cells and stimulating toll-like receptors, these bacteria can cause hepatic inflammation, which can result in fibrogenesis and the production of cytokines [4] [7]. The expansion of oral bacteria in cirrhosis is associated with hepatic encephalopathy and systemic endotoxemia. Survival and colonization of the gut or oral microorganisms may be facilitated by impaired salivary flow and decreased gastric acidity, which are frequent in cirrhotic patients [9] [18]. In order to manage chronic liver disease, oral care and periodontal therapy have been suggested as supplementary approaches [20].

Public Health Relevance

Error creating thumbnail: File missing
This table shows the effect of a high fat diet on microbes in the intestines . Photo credit: [[15]]

Beyond clinical pathology, the mouth-gut microbial axis has wider public health consequences. Despite mounting evidence that links oral microbial dysbiosis to systemic diseases, particularly gastrointestinal problems, oral health is frequently disregarded in public health policy [9] [20]. Financial limitations, restricted access to dental treatment, and ignorance are some of the common obstacles marginalized groups encounter when it comes to oral healthcare. Through the oral gut axis, these differences increase sensitivity to systemic illnesses by causing abnormalities in the oral microbiota [19] [13]. Because of salivary diagnostics, the oral-gut axis presents a viable avenue for early illness identification. Saliva contains oral microbes linked to gastrointestinal disorders, including the ones previously mentioned above. This provides a convenient and non-invasive method for screening at the population level [14] [12] [8]. In low-resource environments where endoscopies or colonoscopies aren’t practical, these instruments are extremely helpful. The oral and intestinal microbiomes are also shaped by nutritional disparity. In food deserts and underprivileged areas, diets high in refined sugars and poor in fiber encourage the growth of harmful bacteria in the gut and the mouth [17] [15]. Therefore, enhancing microbial balance and lowering the burden of disease are two advantages of public health initiatives that support improved nutrition. Additionally, microbial ecosystems are disrupted, and underprivileged populations are disproportionately affected by antibiotic abuse and environmental exposures. Antibiotic overuse can cause gut and mouth dysbiosis, which compromises mucosal immunity and promotes inflammation and microbial translocation [22] [6]. Integrated public health approaches that connect systemic disease prevention, oral health, and microbiome science are needed to address these issues. The significance of interdisciplinary cooperation in healthcare policy is further highlighted by the oral-gut axis. A more comprehensive strategy for illness prevention and health equity may be promoted by initiatives that combine dental with gastrointestinal, community health services, and nutrition [18] [23]. Lastly, finding microbiome education and public outreach might increase knowledge of the connections between nutrition, dental hygiene, and systemic health, enabling people and communities to take charge of their own health [16] [10].

Research Implications and Future Directions

Future studies that connect fundamental discoveries with clinical and public health aspects are necessary, given the increasing awareness of the oral-gut microbiome axis. Utilizing this axis to enhance therapeutic interventions, health policy, and diagnostics is the goal of several exciting new directions. The field of microbiome-based diagnostics is one of the most fascinating. Microbial indicators for gastrointestinal disorders can be found in stool and saliva, which are rich, non-invasive biospecimens. Given their prior associations with inflammatory bowel illness and colorectal cancer, oral infections such as P. gingivalis and Fusobacterium nucleatum may be useful in early diagnosis [14] [6]. Establishing these microbial signatures in a variety of populations and integrating them into standard screening procedures should be the main goals of future research. Further, probiotics and prebiotics that target the gut and oral flora present encouraging treatment options. The gut has been the focus of the majority of probiotic research; however, oral-targeted probiotics, such as those that support beneficial bacteria or inhibit harmful ones, may minimize downstream GI effects and reduce microbial dysbiosis at their source [20] [5]. It may be advantageous to implement interventions that promote microbial resilience in both settings. Advanced studies involving microbial gene expression (metagenomics) are crucial to comprehend the roles of microbiota. Beyond taxonomy, these techniques allow researchers to examine the metabolic pathways and virulence factors that might be an influence on disease. Research using this metatranscriptomics to study oral-gut interactions may uncover new therapeutic targets by illuminating the molecular conversations between host tissues and microbial populations [12] [3]. Policy actions are crucial on a larger scale. Current gaps between dentistry and medical practices should be closed by more explicitly integrating oral health into general healthcare systems, such as routine screening for oral microbes as part of GI-related risk assessments [13]. Microbial imbalances that lead to inequities in chronic disease can also be lessened by public health policies that prioritize access to wholesome food, clean water, and oral hygiene [17] [19]. Lastly, multidisciplinary cooperation will be essential. More thorough models of care and research are anticipated as dentists, public health specialists, microbiologists, and GI specialists come together. Early diagnosis and more successful treatments may result from programs that teach medical professionals from a variety of professions to understand the connection between gastrointestinal and dental health [10] [23].

Conclusion

Fundamental to these findings is the realization that microbial health must be viewed in a comprehensive manner. Because of the tight relationship, the oral and gut microbiomes impact not only localized inflammation and the course of disease, but also overall health outcomes. Having coordinated models that recognize oral health as an essential component of overall health is crucial. This research has ramifications for everyday living and public health in addition to medicine. A more comprehensive approach to lowering the burden of disease includes more emphasis on microbiome-friendly diet, better access to dental care, and public policies that promote microbial diversity and hygiene. As we proceed, utilizing microbiome science to create healthier communities will require cooperative research and policy change.

References

  1. ↑ 1.0 1.1 [Barko, P. C., McMichael, M. A., Swanson, K. S., & Williams, D. A. (2018). The gastrointestinal microbiome: a review. Journal of Veterinary Internal Medicine, 32(1), 9-25.]
  2. ↑ 2.0 2.1 2.2 2.3 [Maki, K. A., Kazmi, N., Barb, J. J., & Ames, N. (2021). The Oral and Gut Bacterial Microbiomes: Similarities, Differences, and Connections. Biological research for nursing, 23(1), 7–20. https://doi.org/10.1177/1099800420941606]
  3. ↑ 3.0 3.1 3.2 3.3 [Kunath, B. J., De Rudder, C., Laczny, C. C., Letellier, E., & Wilmes, P. (2024). The oral–gut microbiome axis in health and disease. Nature Revie18][1ws Microbiology, 22(12), 791-805.]
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 [Lam, G. A., Albarrak, H., McColl, C. J., Pizarro, A., Sanaka, H., Gomez-Nguyen, A., ... & Paes Batista da Silva, A. (2023). The oral-gut axis: periodontal diseases and gastrointestinal disorders. Inflammatory bowel diseases, 29(7), 1153-1164.]
  5. ↑ 5.0 5.1 5.2 5.3 5.4 [Elzayat, H., Mesto, G., & Al-Marzooq, F. (2023). Unraveling the impact of gut and oral microbiome on gut health in inflammatory bowel diseases. Nutrients, 15(15), 3377.]
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 [Park, S. Y., Hwang, B. O., Lim, M., Ok, S. H., Lee, S. K., Chun, K. S., Park, K. K., Hu, Y., Chung, W. Y., & Song, N. Y. (2021). Oral-Gut Microbiome Axis in Gastrointestinal Disease and Cancer. Cancers, 13(9), 2124. https://doi.org/10.3390/cancers13092124]
  7. ↑ 7.0 7.1 7.2 [Wang, A., Zhai, Z., Ding, Y., Wei, J., Wei, Z., & Cao, H. (2024). The oral-gut microbiome axis in inflammatory bowel disease: from inside to insight. Frontiers in Immunology, 15, 1430001.]
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 [Kodukula, K., Faller, D.V., Harpp, D.N., Kanara, I., Pernokas, J., Pernokas, M., Powers, W.R., Soukos, N.S., Steliou, K. and Moos, W.H., 2017. Gut microbiota and salivary diagnostics: the mouth is salivating to tell us something. BioResearch open access, 6(1), pp.123-132.]
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 [Abdelbary, M. M., Hatting, M., Bott, A., Dahlhausen, A., Keller, D., Trautwein, C., & Conrads, G. (2022). The oral-gut axis: Salivary and fecal microbiome dysbiosis in patients with inflammatory bowel disease. Frontiers in Cellular and Infection Microbiology, 12, 1010853.]
  10. ↑ 10.0 10.1 10.2 10.3 [Liu, S., Wang, S., Zhang, N., & Li, P. (2024). The oral microbiome and oral and upper gastrointestinal diseases. Journal of Oral Microbiology, 16(1), 2355823.]
  11. ↑ 11.0 11.1 [Xia, M., Lei, L., Zhao, L. et al. The dynamic oral–gastric microbial axis connects oral and gastric health: current evidence and disputes. npj Biofilms Microbiomes 11, 1 (2025). https://doi.org/10.1038/s41522-024-00623-4]
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 [Kitamoto, S., Nagao-Kitamoto, H., Hein, R., Schmidt, T. M., & Kamada, N. (2020). The bacterial connection between the oral cavity and gut diseases. Journal of dental research, 99(9), 1021-1029.]
  13. ↑ 13.0 13.1 13.2 13.3 13.4 13.5 13.6 13.7 [Yamazaki, K., & Kamada, N. (2024). Exploring the oral-gut linkage: Interrelationship between oral and systemic diseases. Mucosal immunology, 17(1), 147-153.]
  14. ↑ 14.0 14.1 14.2 14.3 14.4 14.5 [Ahn, J., Chen, C. Y., & Hayes, R. B. (2012). Oral microbiome and oral and gastrointestinal cancer risk. Cancer Causes & Control, 23, 399-404.]
  15. ↑ 15.0 15.1 15.2 15.3 [Tong, Y., Gao, H., Qi, Q., Liu, X., Li, J., Gao, J., ... & Wang, C. (2021). High-fat diet, gut microbiome, and gastrointestinal cancer. Theranostics, 11(12), 5889]
  16. ↑ 16.0 16.1 16.2 16.3 [Contaldo, M., Fusco, A., Stiuso, P., Lama, S., Gravina, A. G., Itro, A., ... & Donnarumma, G. (2021). Oral microbiota and salivary levels of oral pathogens in gastro-intestinal diseases: current knowledge and exploratory study. Microorganisms, 9(5), 1064.]
  17. ↑ 17.0 17.1 17.2 17.3 [Huang, K., Wu, L., & Yang, Y. (2021). Gut microbiota: An emerging biological diagnostic and treatment approach for gastrointestinal diseases. JGH Open: an Open Access Journal of Gastroenterology and Hepatology, 5(9), 973.]
  18. ↑ 18.0 18.1 18.2 [Khor, B., Snow, M., Herrman, E., Ray, N., Mansukhani, K., Patel, K. A., ... & Machida, C. A. (2021). Interconnections between the oral and gut microbiomes: reversal of microbial dysbiosis and the balance between systemic health and disease. Microorganisms, 9(3), 496.]
  19. ↑ 19.0 19.1 19.2 19.3 [Singh, H., Torralba, M. G., Moncera, K. J., DiLello, L., Petrini, J., Nelson, K. E., & Pieper, R. (2019). Gastrointestinal and oral microbiome signatures associated with healthy aging. Geroscience, 41(6), 907-921.]
  20. ↑ 20.0 20.1 20.2 20.3 20.4 20.5 [Elghannam, M. T., Hassanien, M. H., Ameen, Y. A., Turky, E. A., ELattar, G. M., ELRay, A. A., & ELTalkawy, M. D. (2024). Oral microbiome dysbiosis and gastrointestinal diseases: a narrative review. Egyptian Liver Journal, 14(1), 32.]
  21. ↑ [Nagao-Kitamoto, H., Kitamoto, S., Kuffa, P., & Kamada, N. (2016). Pathogenic role of the gut microbiota in gastrointestinal diseases. Intestinal research, 14(2), 127-138.]
  22. ↑ 22.0 22.1 [Gorkiewicz, G., & Moschen, A. (2018). Gut microbiome: a new player in gastrointestinal disease. Virchows Archiv, 472(1), 159-172.]
  23. ↑ 23.0 23.1 23.2 [Tan, X., Wang, Y., & Gong, T. (2023). The interplay between oral microbiota, gut microbiota and systematic diseases. Journal of Oral Microbiology, 15(1), 2213112.]



Authored by Olivia Gumz for BIOL 238 Microbiology, taught by Joan Slonczewski,at Kenyon College,2025

Retrieved from "https://microbewiki.kenyon.edu/index.php?title=From_Mouth_to_Gut:_Microbial_Relationships_and_Human_Health&oldid=175530"