This article may be unbalanced toward certain viewpoints. Please improve the article by adding information on neglected viewpoints, or discuss the issue on the talk page.(June 2015)
Thrush, a common condition caused by overgrowth of the fungus Candida albicans. Cases are characterized by growth of matted, yellow-white patches of fungus in the mouth.
Oral microbiology is the study of the microorganisms (microbiota) of the oral cavity and their interactions between oral microorganisms or with the host.[1] The environment present in the human mouth is suited to the growth of characteristic microorganisms found there. It provides a source of water and nutrients, as well as a moderate temperature.[2] Resident microbes of the mouth adhere to the teeth and gums to resist mechanical flushing from the mouth to stomach where acid-sensitive microbes are destroyed by hydrochloric acid.[2][3]
Oral bacteria have evolved mechanisms to sense their environment and evade or modify the host. Bacteria occupy the ecological niche provided by both the tooth surface and mucosal epithelium.[7][8] Factors of note that have been found to affect the microbial colonization of the oral cavity include the pH, oxygen concentration and its availability at specific oral surfaces, mechanical forces acting upon oral surfaces, salivary and fluid flow through the oral cavity, and age.[8] However, a highly efficient innate host defense system constantly monitors the bacterial colonization and prevents bacterial invasion of local tissues. A dynamic equilibrium exists between dental plaque bacteria and the innate host defense system.[7] Of particular interest is the role of oral microorganisms in the two major dental diseases: dental caries and periodontal disease.[7]
Oral microflora
Oral Microbiology Lab Analysis Report.
The oral microbiome, 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. The environment present in the human mouth allows the growth of characteristic microorganisms found there. It provides a source of water and nutrients, as well as a moderate temperature.[2] Resident microbes of the mouth adhere to the teeth and gums to resist mechanical flushing from the mouth to stomach where acid-sensitive microbes are destroyed by hydrochloric acid.[2][3]
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.[11]
Dental plaque
The dental plaque is made up of the microbial community that is adhered to the tooth surface; this plaque is also recognized as a biofilm. While it is said that this plaque is adhered to the tooth surface, the microbial community of the plaque is not directly in contact with the enamel of the tooth. Instead, bacteria with the ability to form attachments to the acquired pellicle, which contains certain salivary proteins, on the surface of the teeth, begin the establishment of the biofilm. Upon dental plaque maturation, in which the microbial community grows and diversifies, the plaque is covered in an interbacterial matrix.[8]
Dental calculus
The calculus of the oral cavity is the result of mineralization of and around dead microorganisms; this calculus can then be colonized by living bacteria. Dental calculus can be present on supragingival and subgingival surfaces.[8]
Oral mucosa
The mucosa of the oral cavity provides a unique ecological site for microbiota to inhabit. Unlike the teeth, the mucosa of the oral cavity is frequently shedding and thus its microbial inhabitants are both kept at lower relative abundance than those of the teeth but also must be able to overcome the obstacle of the shedding epithelia.[8]
Tongue
Unlike other mucosal surfaces of the oral cavity, the nature of the top surface of the tongue, due in part to the presence of numerous papillae, provides a unique ecological niche for its microbial inhabits. One important characteristic of this habitat is that the spaces between the papillae tend to not receive much, if any, oxygenated saliva, which creates an environment suitable for microaerophilic and obligate anaerobic microbiota.[12]
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.[13][11] Further acquisition is determined by diet, developmental accomplishments, general lifestyle habits, hygiene, and the use of antibiotics.[13] Breastfed infants are noted to have higher oral lactobacilli colonization than their formula-fed counterparts.[11] 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.[11][13]
Factors of microbial colonization
Saliva plays a considerable role in influencing the oral microbiome.[14] 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.[15][16]
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.[17]
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.[18]
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.[19]
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.[20] There are many factors that influence the diversity of the oral microbiota, such as age, diet, hygiene practices, and genetics.[21]
Of particular interest is the role of oral microorganisms in the two major dental diseases: dental caries and periodontal disease.[7] There are many factors of oral health which need to be preserved in order to prevent pathogenesis of the oral microbiota or diseases of the mouth. Dental plaque is the material that adheres to the teeth and consists of bacterial cells (mainly S. mutans and S. sanguis), salivary polymers and bacterial extracellular products. Plaque is a biofilm on the surfaces of the teeth. This accumulation of microorganisms subject the teeth and gingival tissues to high concentrations of bacterial metabolites which results in dental disease. If not taken care of, via brushing or flossing, the plaque can turn into tartar (its hardened form) and lead to gingivitis or periodontal disease. In the case of dental cavities, proteins involved in colonization of teeth by Streptococcus mutans can produce antibodies that inhibit the cariogenic process which can be used to create vaccines.[18]
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.[24] Dental plaque is associated with two extremely common oral diseases, dental caries and periodontal disease.[25] 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.[26] Insufficient brushing and flossing can lead to gum and tooth disease, and eventually tooth loss.[24]
The oral environment (temperature, humidity, pH, nutrients, etc.) impacts the selection of adapted (and sometimes pathogenic) populations of microorganisms.[27] 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.[27][28] 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.[29] 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.[30]
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).[31]
Evolution
The evolution of the human oral microbiome can be traced through time via the sequencing of dental calculus (essentially fossilized dental plaque).[32]
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.[32] There have also been similarities in oral microbiota across hominins, as well as other primate species. While a core microbiome consisting of specific bacteria exists across most individuals, significant variation can arise depending on an individual’s unique environment, lifestyle, physiology, and heritage.[33]
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.[32]
Pre-Mesolithic
Relationship to primates
Ancient humans are thought to have maintained a much different oral microbiome landscape than non-human primates, despite having a shared environment. Existing data has found that chimpanzees maintain higher levels of Bacteroidetes and Fusobacteria, while humans have greater proportions of Firmicutes and Proteobacteria.[32] Human oral microbiota have also been found to be less diverse when compared with other primates.[32]
Relationship to hominins
Of the hominins (Homo erectus, Neanderthals, Denisovans) Neanderthal oral microbiomes have been studied in the greatest detail. A cluster of oral microbiota has been found to be shared across Spanish Neanderthals, foraging humans from ~3000 years ago, and a single wild-caught chimpanzee. Similarities have also been found between a meat-eating Neanderthal in Belgium, and hunter humans in Europe and Africa. Ozga et al. (2019) found that Neanderthals and humans share similar oral microbiota, and are more alike to each other than to chimpanzees. Weyrich (2021) finds that these observations suggest humans shared an oral microbiota with Neanderthals until at least 3000 years ago. While it is possible that humans and Neanderthals shared oral microbiota from the moment of separation (~700,000 years ago) until their extinction, Weyrich finds that an equally likely hypothesis is that convergent evolution accounted for similar oral microbiotas across Neanderthals and humans for that period.[34]
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.[32]
The Medieval period: a period of stability
Transitioning from the Neolithic to the Medieval period, which began around 400 years ago, there was little change in the composition of the oral microbiota. This period of stability suggests that despite advancements in agriculture and societal structures, the oral microbiome remained relatively constant. This period did not bring about significant shifts in oral microbial communities, indicating a sort of equilibrium had been reached.[32]
The Industrial Revolution: a modern dilemma
The Industrial Revolution, starting around 1850, brought about another significant shift in human lifestyle and, consequently, the oral microbiome. The widespread availability of industrially processed flour and sugar led to a predominance of cariogenic bacteria in the oral environment. This shift has persisted to the present day, making the modern oral microbiome less diverse than ever before, rendering it less resilient to perturbations in the form of dietary imbalances or invasion by pathogenic bacterial species.[32]
Implications for modern health
The shifts in the oral microbiome through time have significant implications for modern health. The current lack of diversity in the oral microbiome makes it more susceptible to imbalances and pathogenic invasions. This, in turn, can lead to a range of oral and systemic health issues, from dental caries to cardiovascular disease. Dental caries affects between 60 and 90% of children and adults in industrialized countries, and has a more severe effect on less industrialized countries with less capable healthcare systems.[35] 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.
A biofilm is a syntrophic community of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPSs). The cells within the biofilm produce the EPS components, which are typically a polymeric combination of extracellular polysaccharides, proteins, lipids and DNA. Because they have a three-dimensional structure and represent a community lifestyle for microorganisms, they have been metaphorically described as "cities for microbes".
Lactobacillus is a genus of gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. Until 2020, the genus Lactobacillus comprised over 260 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus assigned lactobacilli to 25 genera.
The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, including the gastrointestinal tract, skin, mammary glands, seminal fluid, uterus, ovarian follicles, lung, saliva, oral mucosa, conjunctiva, and the biliary tract. Types of human microbiota include bacteria, archaea, fungi, protists, and viruses. Though micro-animals can also live on the human body, they are typically excluded from this definition. In the context of genomics, the term human microbiome is sometimes used to refer to the collective genomes of resident microorganisms; however, the term human metagenome has the same meaning.
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors, from yellow to black. Symptoms may include pain and difficulty eating. Complications may include inflammation of the tissue around the tooth, tooth loss and infection or abscess formation. Tooth regeneration is an ongoing stem cell–based field of study that aims to find methods to reverse the effects of decay; current methods are based on easing symptoms.
Streptococcus mutans is a facultatively anaerobic, gram-positive coccus commonly found in the human oral cavity and is a significant contributor to tooth decay. The microbe was first described by James Kilian Clarke in 1924.
Dental plaque is a biofilm of microorganisms that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found between the teeth, on the front of teeth, behind teeth, on chewing surfaces, along the gumline (supragingival), or below the gumline cervical margins (subgingival). Dental plaque is also known as microbial plaque, oral biofilm, dental biofilm, dental plaque biofilm or bacterial plaque biofilm. Bacterial plaque is one of the major causes for dental decay and gum disease.
The dental pellicle, or acquired pellicle, is a protein film that forms on the surface enamel, dentin, artificial crowns, and bridges by selective binding of glycoproteins from saliva that prevents continuous deposition of salivary calcium phosphate. It forms in seconds after a tooth is cleaned, or after chewing. It protects the tooth from the acids produced by oral microorganisms after consuming carbohydrates.
Dysbiosis is characterized by a disruption to the microbiome resulting in an imbalance in the microbiota, changes in their functional composition and metabolic activities, or a shift in their local distribution. For example, a part of the human microbiota such as the skin flora, gut flora, or vaginal flora, can become deranged (unbalanced), when normally dominating species become underrepresented and species that normally are outcompeted or contained increase to fill the void. Similar to the human gut microbiome, diverse microbes colonize the plant rhizosphere, and dysbiosis in the rhizosphere, can negatively impact plant health. Dysbiosis is most commonly reported as a condition in the gastrointestinal tract or plant rhizosphere.
Oral hygiene is the practice of keeping one's oral cavity clean and free of disease and other problems by regular brushing of the teeth and adopting good hygiene habits. It is important that oral hygiene be carried out on a regular basis to enable prevention of dental disease and bad breath. The most common types of dental disease are tooth decay and gum diseases, including gingivitis, and periodontitis.
Willoughby Dayton Miller (1853–1907) was an American dentist and the first oral microbiologist.
Oral ecology is the microbial ecology of the microorganisms found in mouths. Oral ecology, like all forms of ecology, involves the study of the living things found in oral cavities as well as their interactions with each other and with their environment. Oral ecology is frequently investigated from the perspective of oral disease prevention, often focusing on conditions such as dental caries, candidiasis ("thrush"), gingivitis, periodontal disease, and others. However, many of the interactions between the microbiota and oral environment protect from disease and support a healthy oral cavity. Interactions between microbes and their environment can result in the stabilization or destabilization of the oral microbiome, with destabilization believed to result in disease states. Destabilization of the microbiome can be influenced by several factors, including diet changes, drugs or immune system disorders.
Streptococcus parasanguinis is a gram-positive bacterium of the genus Streptococcus that is classified as a member of the Streptococcus viridans group. S. parasanguinis is one of the major early colonizers of dental surfaces in the human oral cavity. Cell surface structures including pili and fimbriae allow the bacteria to adhere to oral surfaces. These adhesion molecules also play an important role in biofilm formation and promote aggregation with late tooth colonizers to form dental plaque. The presence of S. parasanguinis in the oral cavity is associated with a healthy microflora.
Biotene is an over-the-counter dental hygiene product currently marketed by Haleon. It is available in various forms, including toothpaste, mouthwash, and gel.
Methanobrevibacter oralis is a methanogenic archaeon species considered to be a member of the human microbiota, mainly associated to the oral cavity. M. oralis is a coccobacillary shaped, single-cell, Gram-positive, non-motile microorganism of the Archaea domain of life. This species has been isolated and sequenced from humans in dental plaque and in their gastrointestinal tract. As a methanogen and a hydrogenotroph, this prokaryote can produce methane by using hydrogen and carbon dioxide as substrates through a process called methanogenesis.
A microbiome is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps et al. as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity". In 2020, an international panel of experts published the outcome of their discussions on the definition of the microbiome. They proposed a definition of the microbiome based on a revival of the "compact, clear, and comprehensive description of the term" as originally provided by Whipps et al., but supplemented with two explanatory paragraphs, the first pronouncing the dynamic character of the microbiome, and the second clearly separating the term microbiota from the term microbiome.
Plaque hypotheses are theories to explain the role of plaque bacteria in dental caries and in periodontal disease. They rely heavily on the postulates of Koch and on the work of Louis Pasteur (1822–1895). Changing perceptions have altered treatment models.
The uterine microbiome refers to the community of commensal, nonpathogenic microorganisms—including bacteria, viruses, and yeasts/fungi—present in a healthy uterus, as well as in the amniotic fluid and endometrium. These microorganisms coexist in a specific environment within the uterus, playing a vital role in maintaining reproductive health. In the past, the uterus was believed to be a sterile environment, free of any microbial life. Recent advancements in microbiological research, particularly the improvement of 16S rRNA gene sequencing techniques, have challenged this long-held belief. These advanced techniques have made it possible to detect bacteria and other microorganisms present in very low numbers. Using this procedure that allows the detection of bacteria that cannot be cultured outside the body, studies of microbiota present in the uterus are expected to increase.
The salivary microbiome consists of the nonpathogenic, commensal bacteria present in the healthy human salivary glands. It differs from the oral microbiome which is located in the oral cavity. Oral microorganisms tend to adhere to teeth. The oral microbiome possesses its own characteristic microorganisms found there. Resident microbes of the mouth adhere to the teeth and gums. "[T]here may be important interactions between the saliva microbiome and other microbiomes in the human body, in particular, that of the intestinal tract."
The evolution of the human oral microbiome is the study of microorganisms in the oral cavity and how they have adapted over time. There are recent advancements in ancient dental research that have given insight to the evolution of the human oral microbiome. Using these techniques it is now known what metabolite classes have been preserved and the difference in genetic diversity that exists from ancient to modern microbiota. The relationship between oral microbiota and its human host has changed and this transition can directly be linked to common diseases in human evolutionary past. Evolutionary medicine provides a framework for reevaluating oral health and disease and biological anthropology provides the context to identify the ancestral human microbiome. These disciplines together give insights into the oral microbiome and can potentially help contribute to restoring and maintaining oral health in the future.
References
↑ Schwiertz A (2016). Microbiota of the human body: implications in health and disease. Switzerland: Springer. p.45. ISBN978-3-319-31248-4.
1 2 Wang ZK, Yang YS, Stefka AT, Sun G, Peng LH (April 2014). "Review article: fungal microbiota and digestive diseases". Alimentary Pharmacology & Therapeutics. 39 (8): 751–766. doi:10.1111/apt.12665. PMID24612332. S2CID22101484. In addition, GI fungal infection is reported even among those patients with normal immune status. Digestive system-related fungal infections may be induced by both commensal opportunistic fungi and exogenous pathogenic fungi.... Candida sp. is also the most frequently identified species among patients with gastric IFI.... It was once believed that gastric acid could kill microbes entering the stomach and that the unique ecological environment of the stomach was not suitable for microbial colonisation or infection. However, several studies using culture-independent methods confirmed that large numbers of acid-resistant bacteria belonging to eight phyla and up to 120 species exist in the stomach, such as Streptococcus sp., Neisseria sp. and Lactobacillus sp. etc.26, 27 Furthermore, Candida albicans can grow well in highly acidic environments,28 and some genotypes may increase the severity of gastric mucosal lesions.29
↑ Marsh PD, Do T, Beighton D, Devine DA (February 2016). "Influence of saliva on the oral microbiota". Periodontology 2000. 70 (1): 80–92. doi:10.1111/prd.12098. PMID26662484.
↑ Pietropaoli D, Del Pinto R, Ferri C, Ortu E, Monaco A (August 2019). "Definition of hypertension-associated oral pathogens in NHANES". Journal of Periodontology. 90 (8): 866–876. doi:10.1002/JPER.19-0046. PMID31090063. S2CID155089995.
↑ Hultberg B, Lundblad A, Masson PK, Ockerman PA (November 1975). "Specificity studies on alpha-mannosidases using oligosaccharides from mannosidosis urine as substrates". Biochimica et Biophysica Acta (BBA) - Enzymology. 410 (1): 156–163. doi:10.1016/0005-2744(75)90216-8. PMID70.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
