Oral microbiology

The oral microbiome, complex and diverse microbial community including (bacteria, viruses, fungi, archaea and protozoa) mainly comprising bacteria which have developed resistance to the human immune system, has been known to impact the host for its own benefit, as seen with dental cavities. Anaerobic bacteria in the oral cavity include: Actinomyces, Arachnia, Bacteroides, Bifidobacterium, Eubacterium, Fusobacterium, Lactobacillus, Leptotrichia, Peptococcus, Peptostreptococcus, Propionibacterium, Selenomonas, Treponema, and Veillonella. The oral cavity of a new-born baby does not contain bacteria but rapidly becomes colonized with bacteria such as Streptococcus salivarius. With the appearance of the teeth during the first year colonization by Streptococcus mutans and Streptococcus sanguinis occurs as these organisms colonise the dental surface and gingiva. Other strains of streptococci adhere strongly to the gums and cheeks but not to the teeth. The gingival crevice area (supporting structures of the teeth) provides a habitat for a variety of anaerobic species. Bacteroides and spirochetes colonize the mouth around puberty. == Ecological sites for oral microbiota ==

As a diverse environment, a variety of organisms can inhabit unique ecological niches present in the oral cavity including the teeth, gingiva, tongue, cheeks, and palates. These different sites support distinct but interconnected communities of microorganisms, insiting their composition is shaped by local conditions and other factors such as diet, age and immune system status. The tongue microbiome is considered as a key component of the oral microbiome, with implications for malodorous mouth, dysbiotic community shifts and modulation of host-immunity responses. == Acquisition of oral microbiota ==

Acquisition of the oral microbiota heavily depends on the route of delivery as an infant – vaginal versus caesarian; upon comparing infants three months after birth, infants born vaginally were reported to have higher oral taxonomic diversity than their cesarean-born counterparts. Further acquisition is determined by diet, developmental accomplishments, general lifestyle habits, hygiene, and the use of antibiotics. Breastfed infants are noted to have higher oral lactobacilli colonization than their formula-fed counterparts. Diversity of the oral microbiome is also shown to flourish upon the eruption of primary teeth and later adult teeth, as new ecological niches are introduced to the oral cavity. == Factors of microbial colonization ==

Saliva plays a considerable role in influencing the oral microbiome. More than 800 species of bacteria colonize oral mucus, 1,300 species are found in the gingival crevice, and nearly 1,000 species comprise dental plaque. The mouth is a rich environment for hundreds of species of bacteria since saliva is mostly water and plenty of nutrients pass through the mouth each day. When kissing, it takes only 10 seconds for no less than 80 million bacteria to be exchanged by the passing of saliva. However, the effect is transitory, as each individual quickly returns to their own equilibrium. Due to progress in molecular biology techniques, scientific understanding of oral ecology is improving. Oral ecology is being more comprehensively mapped, including the tongue, the teeth, the gums, salivary glands, etc. which are home to these communities of different microorganisms. The host's immune system controls the bacterial colonization of the mouth and prevents local infection of tissues. A dynamic equilibrium exists notably between the bacteria of dental plaque and the host's immune system, enabling the plaque to stay behind in the mouth when other biofilms are washed away. In equilibrium, the bacterial biofilm produced by the fermentation of sugar in the mouth is quickly swept away by the saliva, except for dental plaque. In cases of imbalance in the equilibrium, oral microorganisms grow out of control and cause oral diseases such as tooth decay and periodontal disease. Several studies have also linked poor oral hygiene to infection by pathogenic bacteria. == Role in health ==

The oral microbiota is largely related to systemic health, and disturbances in the oral microbiota can lead to diseases in both the oral cavity and the rest of the body. There are many factors that influence the diversity of the oral microbiota, such as age, diet, hygiene practices, and genetics. Oral microorganisms play a significant role in the two major dental diseases, dental caries and periodontal disease. Genera of fungi that are frequently found in the mouth include Candida, Cladosporium, Aspergillus, Fusarium, Glomus, Alternaria, Penicillium, and Cryptococcus, among others. Importance of dental hygiene One of the most important factors in promoting optimal oral microbiota health is the use of good oral hygiene practices. To prevent any possible complication from an altered oral microbiota, it is important to brush and floss every day, schedule regular cleanings, eat a healthy diet, and replace toothbrushes frequently. Consistent toothbrushing and flossing is essential for disrupting harmful plaque formation. Research has shown that flossing is associated with a decrease in the bacteria Streptococcus mutans which has been shown to be involved in cavity formation. Insufficient brushing and flossing can lead to gum and tooth disease, and eventually tooth loss. In addition, poor dental hygiene has been linked to conditions such as osteoporosis, diabetes and cardiovascular diseases. == Issues and areas of research ==

The oral environment (temperature, humidity, pH, nutrients, etc.) impacts the selection of adapted (and sometimes pathogenic) populations of microorganisms. For a young person or an adult in good health and with a healthy diet, the microbes living in the mouth adhere to mucus, teeth and gums to resist removal by saliva. Eventually, they are mostly washed away and destroyed during their trip through the stomach. Salivary flow and oral conditions vary person-to-person, and also relative to the time of day and whether or not an individual sleeps with their mouth open. From youth to old age, the entire mouth interacts with and affects the oral microbiome. Via the larynx, numerous bacteria can travel through the respiratory tract to the lungs. There, mucus is charged with their removal. Pathogenic oral microflora have been linked to the production of factors which favor autoimmune diseases such as psoriasis and arthritis, as well as cancers of the colon, lungs and breasts. == Intercellular communication ==

Most of the bacterial species found in the mouth belong to microbial communities, called biofilms, a feature of which is inter-bacterial communication. Cell–cell contact is mediated by specific protein adhesins and often, as in the case of inter-species aggregation, by complementary polysaccharide receptors. Another method of communication involves cell–cell signalling molecules, which are of two classes: those used for intra-species and those used for inter-species signalling. An example of intra-species communication is quorum sensing. Oral bacteria have been shown to produce small peptides, such as competence stimulating peptides, which can help promote single-species biofilm formation. A common form of inter-species signalling is mediated by 4, 5-dihydroxy-2, 3-pentanedione (DPD), also known as autoinducer-2 (Al-2). == Evolution ==

The evolution of the human oral microbiome can be traced through time via the sequencing of dental calculus (essentially fossilized dental plaque). As mentioned in prior sections, the human oral microbiome has important implications for the health and wellness of human beings overall, and is often the only surviving health record for ancient populations. The oral microbiome has evolved over time alongside humans, in response to changes in diet, lifestyle, environment, and even the advent of cooking. Considering that oral bacteria are transferred vertically from primary caregivers in early childhood, and horizontally between family members later in life, archaeological dental calculus is a unique way to trace population structure, movement, and admixture between ancient cultures, as well as the spread of disease. Major shifts through archaeological periods The human oral microbiome has been a subject of increasing scientific scrutiny, especially in understanding its evolutionary journey. The oral microbiome has undergone significant shifts in composition, particularly during key historical periods like the Neolithic and the Industrial Revolution. The Neolithic revolution: a turning point The Neolithic period began around 10,000 years ago and marked a significant turning point in human history. This era saw the shift from a hunter-gatherer lifestyle to agriculture and farming. One of the most significant changes during this period was the adoption of carbohydrate-rich diets, particularly the consumption of domesticated cereals like wheat and barley. This shift had a profound impact on the oral microbiome. The increase in fermentable carbohydrates led to a surge in dental caries, a common oral health issue. Additionally, the Neolithic period also witnessed a reduction in microbial diversity in the oral environment. An understanding of the oral microbiome, via an examination of the evolution of the oral microbiome, can help science understand past errors and help inform the best path forward in sustainable healthcare interventions that work proactively with the body's natural systems, rather than fighting them with intermittent reactive interventions. == See also ==