.png)
History of the Human Microbiome
The human microbiome is the collection of all the microorganisms living in association with the human body [1] including distinct communities of bacteria, fungi, viruses, archaea, protists, and other microorganisms whose compositions are dependent on various factors such as location and/or environmental influence [8].
The study of the human microbiome began with Antonie van Leewenhoek, the “father of microbiology”, in the 1680s [7]. So, although the discussion of the microbiome may seem new, it has actually been around since the very beginning of microbiological studies. The new emphasis on the study of the human microbiome now focuses more on the use of powerful molecular techniques to gain insight into differences [7] that exist within the microbiome and to better understand changes that take place throughout the body under certain conditions.
A research project called The Human Microbiome Project (HMP) was “supported by the National Institute of Health (NIH) Common Fund from 2007 through 2016 with the mission of generating resources that would enable the comprehensive characterization of the human microbiome and analysis of its role in human health and disease [1].”
The HMP was split into two phases, HMP1 and HMP2. The different phases recorded changes in microbial community composition viromics, metabolomic profiles, gene expression, and protein profiles for both the host and microbiome, and host-specific properties such as genetic, epigenetic, antibody, and cytokine profiles [5]
HMP1 - focused on the characterization of microbial communities from numerous body sites in a baseline study of healthy adult subjects
HMP2 - expanded knowledge of biological properties analyzed for both the host and microbiome for three microbiome-associated conditions
Pregnancy and preterm birth
Inflammatory bowel diseases
Prediabetes
[5]
From decades of research, it is known that different sites throughout the human body are comprised of unique biomes with drastically different environments and nutrient availability and vary between individuals in different states of health [8].
The two largest studied microbiomes within the human body
are the gut and the oral cavity.
The focus of this discussion will be on the oral microbiome — what it is, how it’s influenced, and why it’s important to overall health.
The Oral Microbiome
When we think of our mouth, we typically imagine teeth, gums, and maybe even the taste of food. However, what’s often overlooked is the complex, dynamic, and ever-changing ecosystem within the oral cavity known as the oral microbiome, which is made up of over 700 different species of bacteria, along with viruses, fungi, and other microorganisms.
[4]
A healthy microbiome supports the body's ability to fight infections, aids in digestion, and maintains balance. But, if there’s an imbalance—where harmful bacteria outnumber the beneficial ones—this dysbiosis can contribute to issues like tooth decay, periodontal diseases, and adverse systemic health conditions.
Oral Microbiome Characteristics
To better understand the oral microbiome, there are specific characteristics to review, including parameters that must be met for oral disease to develop.
First, one of the fundamental takeaways for understanding the oral microbiome is knowing that there are nine distinct regions within the oral cavity that house their own unique microbiomes based on physical and chemical properties specific to each site [6]
Palatine tonsils
Tongue dorsum
Throat
Attached gum
Hard palate
Buccal mucosa
Supragingival tooth structure
Subgingival tooth structure
Saliva
[6]
The changes that take place in each of the nine oral microbiome regions have a significant impact on the development of a chronic inflammatory response and subsequent diseases in both the oral cavity and systemically.
All organ systems within the human body are connected, and a disruption of the oral microbiome results in a subsequent disruption throughout the entire body, and vice versa.
In terms of periodontal disease, two factors must be met for the disease process to occur
Oral dysbiosis with an overgrowth of pathogenic bacteria
A susceptible host body
Once bacterial overgrowth has begun, the host’s body generates an immune response to the bacterial infection in the oral cavity, which results in periodontal diseases such as gingivitis or periodontitis [2]
Overall, periodontitis is a multifactorial inflammatory disease that results in an imbalance of bacterial species within dental biofilms and favors the establishment of chronic inflammatory conditions that ultimately destroy tooth-supporting tissues [2].
Although all nine regions within the oral cavity will see a shift in their microbial balance during dysbiosis, the changes that result in periodontitis and subsequent tooth loss from the progression of the disease occur mainly within the hard-to-reach areas such as the subgingival sulcus surrounding teeth. This is where routine preventative dental appointments are essential in oral health.
Only a trained dental professional is able to reach and remove the pathogenic bacteria hidden within the biofilms throughout different regions of the oral cavity. However, below is a list of helpful habits patients are able to implement to assist in maintaining a healthy oral microbiome
Proper Home Care Routines
Brush with an electric toothbrush twice per day
Floss with expanding string floss once per day
Tonge scrape once per day
Use an oral irrigator such as a water flosser three days per week
Avoiding routine use of antimicrobial mouthwashes
Increase Probiotic-Rich Foods
Fermented foods like yogurt, kefir, and sauerkraut contain beneficial bacteria that can support the growth of good microbes in the mouth and gut
Limit Sugar and Processed Foods
High-sugar foods feed harmful bacteria that contribute to cavities and gum disease, so opt for whole foods, fruits, and vegetables instead
Stay Hydrated
Drinking plenty of water helps wash away food particles and bacteria from the mouth and helps neutralize oral pH levels, which promotes a healthy oral environment
Avoid Tobacco and Limit Alcohol
Both smoking and excessive alcohol consumption can negatively impact the oral microbiome. If possible, avoid or reduce their use
Routine Dental Visits
Regular check-ups allow trained dental professionals to monitor oral health and identify any potential issues early on
Second, it’s also essential to understand that the oral microbiome is highly dynamic and can change based on a variety of factors such as diet, lifestyle, age, and oral hygiene habits.
[3]
Many factors can disrupt the delicate balance of the oral microbiome. Some of the most common include the following
Diet - Diets high in sugar and processed foods can promote the growth of harmful bacteria that contribute to tooth decay and periodontal disease. On the other hand, a diet rich in fiber, fruits, vegetables, and probiotics can support a healthy microbiome.
Oral Hygiene - Proper tooth brushing, tongue scraping, flossing, and regular visits to the dentist help maintain a balanced microbiome by reducing harmful plaque and bacteria buildup.
Smoking and Alcohol Consumption - Smoking is known to reduce the number of beneficial bacteria in the mouth, while alcohol can alter the oral environment by drying out the mouth and promoting the growth of harmful bacteria.
Antibiotic Use - While antibiotics are essential for treating infections, overuse can kill off beneficial bacteria in the mouth and allow harmful bacteria to proliferate.
Medication Use - A common side effect seen with several medications includes a decrease in salivary flow rates, which dry out the mouth and promotes the growth of harmful bacteria
Antimicrobial Mouthwash - research over the last decade has shown that routine use of an antimicrobial mouthwash can contribute to imbalances of the oral microbiome that subsequently harm systemic health
For example, frequent use of antimicrobial mouthwashes causes a disruption of oral nitric oxide levels, which increases the risk of poor cardiovascular health and can lead to an increase in blood pressure
Oral Microbiome & Systemic Health
As an overview, research has revealed a strong connection between oral dysbiosis and several systemic diseases, including but not limited to the following
Cardiovascular Disease - Certain oral bacteria can enter the bloodstream, contributing to the development of heart disease, clogged arteries, and even stroke
Studies suggest that bacteria such as Porphyromonas gingivalis, which is associated with periodontal disease, may trigger inflammatory responses that damage blood vessels and increase heart disease risk
Diabetes - Poor oral hygiene and gum disease may make it harder to control blood sugar levels
Additionally, the inflammation caused by gum disease can interfere with the body’s ability to use insulin effectively
Pregnancy Complications - Gum disease has been linked to premature birth and low birth weight
The inflammation caused by oral bacteria may affect the placenta and other pregnancy-related factors
Respiratory Health - Aspiration pneumonia and other lung diseases can occur when harmful oral bacteria are inhaled into the lungs, especially in individuals with poor oral hygiene or compromised immune systems
Check my blog listings for more in-depth discussions on how oral dysbiosis impacts individual body systems & to find more details on specific bacterial strains and their impact on systemic health.
An emerging focus in the practice of dentistry is the idea of maintaining a balanced oral microbiome through strategic, individualized in-office and at-home therapies. These therapies and updated protocols are designed to aid in bacterial symbiosis and homeostasis as a way to prevent the development and progression of oral and systemic complications.
Because of the interconnected nature of oral and systemic health, it’s imperative that oral health education for patients begins at a young age. Helping children create habits that support a healthy mouth such as routine dental visits, proper home care routines, and eating healthy foods sets a strong foundation to support lifelong whole-body health. Further, adults who have been diagnosed with any form of oral or systemic dysbiosis can also benefit greatly from improving oral care habits and adjusting lifestyle routines to better support whole-body health.
We cannot have overall health if the mouth is harboring bacteria and disease. For optimal long-term, whole-body health, it’s essential that we start treating the body and mouth as one connected entity.
Talk soon,
Liz Laney, BSDH, RDH
Oral-Systemic RDH & Educator
Have questions about periodontal disease and systemic health or want to know more? Check out the forum and start a conversation!
Sources
About the human microbiome. NIH Human Microbiome Project. https://www.hmpdacc.org/overview/.
Fragkioudakis I, Riggio MP, Apatzidou DA. Understanding the microbial components of periodontal diseases and periodontal treatment-induced microbiological shifts. Journal of Medical Microbiology. 2020;70(1). doi:10.1099/jmm.0.001247
Rosier BT, Marsh PD, Mira A. Resilience of the Oral Microbiota in Health: Mechanisms That Prevent Dysbiosis. Journal of Dental Research. 2018;97(4):371-380. doi:10.1177/0022034517742139
Santonocito S, Giudice A, Polizzi A, Troiano G, Merlo EM, Sclafani R, Grosso G, Isola G. A Cross-Talk between Diet and the Oral Microbiome: Balance of Nutrition on Inflammation and Immune System’s Response during Periodontitis. Nutrients. 2022; 14(12):2426. https://doi.org/10.3390/nu14122426
The Integrative HMP (iHMP) Research Network Consortium. The Integrative Human Microbiome Project. Nature 569, 641–648 (2019). https://doi.org/10.1038/s41586-019-1238-8
Tian S, Ding T, Li H. Oral microbiome in human health and diseases. mLife. 2024;3(3):367-383. doi:10.1002/mlf2.12136
Ursell LK, Metcalf JL, Parfrey LW, Knight R. Defining the human microbiome. Nutr Rev. 2012;70 Suppl 1(Suppl 1):S38-S44. doi:10.1111/j.1753-4887.2012.00493.x
Willis JR, Gabaldón T. The Human Oral Microbiome in Health and Disease: From Sequences to Ecosystems. Microorganisms. 2020; 8(2):308. https://doi.org/10.3390/microorganisms8020308