The Oral Microbiota and Systemic Health

The human oral microbiota is represented by the community of commensal, symbiotic, and pathogenic microorganisms which are normally found in the oral cavity.

The oral microbiota is found in saliva, the surface of gum tissue and teeth, and in biofilms, which are basically layers of goop-like material made of exopolysaccharides or EPS, within which bacteria survive in a quiescent or slow-growing state.

These microbes play an important role in maintaining oral homeostasis, protecting the oral cavity and preventing disease development.

Now, the oral microbiota can be classified into a core microbiota and a variable microbiota. The core microbiota is the same for all individuals, while the variable microbiota is different between individuals in response to unique lifestyles and phenotypic and genotypic determinants.

The oral cavity contains over 700 microbial species as well as commensal and opportunistic bacteria, archaea, fungi, protozoa and viruses which are organized into different microbial habitats including the hard palate, tongue dorsum, saliva, palatine tonsils, throat, buccal mucosa, keratinised gingiva, supragingival plaque, subgingival plaque, lips and even dentures!

The major genera with the largest representation in oral cavities include Streptococcus, Prevotella, Haemophilus, Rothia, Veillonella, Neisseria, Fusobacterium and Porphyromonas.

Now, the oral microbiota can be altered by a series of endogenous and exogenous factors such as diet, smoking, alcohol, antibiotics, or pregnancy.

This alteration can disrupt the bacterial equilibrium in the oral cavity by increasing harmful bacteria and decreasing the beneficial ones, thus leading to a series of oral infectious diseases such as dental caries or periodontal diseases.

So, a sugar rich diet and frequent snacks can lead to dental caries, while a diet with increased fibrous foods and dairy products help maintain a healthy balance in the oral microbiota.

Smoking can alter the oral microbiota by increasing the acidity of saliva, depleting oxygen, influencing oral bacterial adherence to mucosal surfaces, and impairing host immunity.

Also, cigarettes actually carry a large number of different bacteria and some of these, such as Bacillus spp. and Clostridium spp.

can survive the smoking process and colonize the oral cavity. Alcohol can lead to an increase in Gram-positive bacteria such as Streptococcus mutans, which can lead to dental caries.

Also, oral bacteria convert ethanol to acetaldehyde which is a carcinogen. However, moderate consumption of red wine may enhance oral health because it contains a mixture of organic acids that are active against oral streptococci responsible for caries development and Streptococcus pyogenes responsible for pharyngitis.

The use of antibiotics can produce changes in the oral microbiota by destroying many bacterial species and decreasing their enzymatic activity.

In pregnancy, the oral microbiota goes through some important changes which lead to colonisation of various microorganisms, especially periodontal pathogens, that may be a risk for the health of the pregnant woman.

Also, some systemic diseases such as diabetes, rheumatoid arthritis and systemic lupus erythematosus can enhance inflammation in the periodontium which can lead to a shift in bacterial composition and increase the risk or severity of periodontitis.

Finally, changes in the oral microbiota can promote development of certain systemic diseases such as cardiovascular disease, pneumonia, pancreatic cancer or colorectal cancer.

So, oral bacteria might increase the risk of esophageal cancer, especially Porphyromonas gingivalis, which has been detected in cancerous tissues.

P. gingivalis is also associated with a high risk of pancreatic cancer along with Aggregatibacter actinomycetemcomitans, and they can be used as an effective biosensor for early diagnosis of pancreatic cancer.

Fusobacteria is another genus of bacteria in the mouth that produces excessive immune responses and activates oncogenes.

They can invade the bowel and cause inflammation that accelerate colorectal tumor formation. Oral bacteria can also contribute to inflammatory diseases such as atherosclerosis or pneumonia.

In atherosclerosis, oral bacteria such as Streptococcus mutans could contribute directly by disrupting endothelial cell function, while periodontal bacteria, such as P.

gingivalis could accelerate the development of atheromatous plaque, by infecting the epithelial cells that produce proinflammatory cytokines which enter the blood circulation and affect the cells in the atheromatous plaques, thus leading to the development of atherosclerosis.

Poor oral hygiene can increase colonisation with pathogens such as S. aureus or P.

aeruginosa that can be aspirated into the lower airway, thus increasing the risk of pneumonia. ##Summary All right, as a quick recap.

The human oral microbiota is represented by the community of microorganisms which are normally found in the oral cavity, and can exist as free-floating bacteria or in the form of a biofilm.

The oral microbiota plays an important role in maintaining oral homeostasis, protecting the oral cavity and preventing disease.

It can be classified into a core microbiota which is the same for all individuals and a variable microbiota which is different between individuals.

The oral microbiota can be altered by a series of endogenous and exogenous factors such as diet, smoking, alcohol, antibiotic treatments or pregnancy.

These changes may increase pathogenic organisms or their activity, causing a series of oral infectious diseases such as dental caries or periodontal diseases.

They can also increase the risk of developing systemic diseases such as cardiovascular disease, pneumonia, pancreatic cancer or colorectal cancer.