Oral Microbiota Composition and Ecology PDF

Microbiology Unit 19 Composition and ecology of oral microbiota Ve más allá 1 Ecosystem Community interaction of living organisms and non-living components of the environment, that act as a system, where energy is exchanged and system-level processes, such as the cycling of elements, emerge. ...

Microbiology Unit 19 Composition and ecology of oral microbiota Ve más allá 1 Ecosystem Community interaction of living organisms and non-living components of the environment, that act as a system, where energy is exchanged and system-level processes, such as the cycling of elements, emerge. Oral cavity Large ecosystem, composed of primary ecosystems or habitats 1. Buccal mucosa (lips, cheek, palate, tongue) 2. Tooth surface (supragingival and subgingival) 3. Acquired salivary pellicle 4. Dental plaque 5. Prosthodontic and orthodontic appliances 6. Gingival sulcus 7. Saliva Ecological interactions  Determine the qualitative and quantitative characteristics of the entire microbiota in the different ecological niches (habitat in which specific interactions occur) and the different situations of health or illness.  Ecosystems are regulated by a series of internal and external factors (eruption or extraction of teeth, the insertion of orthodontic bands or dentures, etc.) Oral ecosystem characteristics  The oral cavity is an open and dynamic ecosystem (it will change during the life of an individual)  Variability: qualitative and quantitative differences among different individuals. Also distinct habitats exist even within the mouth of the same individual, each of which will support the growth of a characteristic microbial community (particular biological features).  Host factors (oral hygiene, diet, ...)  Type and characteristics of the microorganisms  Physicochemical factors (pH, moisture, ...)  Heterogeneity: a large number of different bacterial species can live within the mouth, in different ecosystems (more than 700 species)  Quantity: eg. 108 bacteria/ml in saliva and 1011-1012 bacteria/g in plaque  Specificity: eg. Streptococcus mutans is present on hard surfaces Oral ecosystems 1. Oral mucosa: • Lips, tongue, cheeks and palate • Lips, cheeks and palate: sparsely colonized (shedding) • Tongue (highly colonized)  Surface covered with papillae  Reservoir of obligate anaerobes 2. Tooth surfaces • Non-shedding surface that facilitates colonization and accumulation of bacteria (dental plaque) • Different surfaces for bacterial colonization • Each dental surface presents different microflora Oral ecosystems 3. Acquired salivary pellicle  Acellular amorphous layer formed by selective adsorption of salivary components on tooth surfaces, particularly glycoproteins and proteins and, in a smaller degree, products secreted by bacteria.  Two main characteristics: 1. Protective: it opposes tooth decalcification, preventing the penetration of acids and the removal of minerals from the tooth enamel surface into the medium. 2. Destructive: allows bacterial colonization. Microorganisms adhere to it to form bacterial plaque. Oral ecosystems 4. Dental plaque:  Biofilm created by microorganisms which adhere to each other and to the tooth surface (through the pellicle), embedded and surrounded by a mixed abiotic material. Its composition varies with the time of evolution and the location: supragingival or coronal; subgingival; root surfaces 5. Prosthodontic and orthodontic appliances  Artificial materials used for dental restoration, orthodontic therapy or any other elements 6. Gingival sulcus  Virtual space formed by the inner part of the marginal gingiva and the tooth surface (enamel or cement). It starts at the free margin of the gingiva, called crevicular epithelium and ends in the deepest point of the junctional epithelium. Oral ecosystems 7. Saliva:  Viscous liquid derived from the major and minor salivary glands that bath oral surfaces  Main function: keep the mouth moist, soften and lubricate food for easier swallowing Factors affecting the growth of oral microorganisms The habitat of the mouth is very varied and is modified according to multiple factors: a. Age b. Anatomical location c. Physico-chemical factors d. Adhesion, aggregation and co-aggregation factors e. Nutritional factors f. Host protective factors g. Antagonistic factors between bacteria Factors affecting the growth of oral microorganisms a. Age The oral environment varies throughout the life of the individual.  Birth: no teeth  Puberty: hormonal changes  Adulthood: caries, gingivitis ...  Elderly: loss of teeth Factors affecting the growth of oral microorganisms b. Anatomical location  Different from mucosal surfaces to hard tissues  Mucosal epithelium shed but hard surfaces do not shed  Hard surfaces: differences between smooth surfaces, cracks, occlusal, interproximal ...  Gingival sulcus is also a special area Factors affecting the growth of oral microorganisms c. Physico-chemical factors Humidity  Water is essential for bacteria  High humidity because of saliva pH  Under normal conditions: between 6.7 and 7.5  Varies greatly depending on:  Sugar-rich foods: low pH  Protein-rich food: pH rises  Saliva buffers pH (bicarbonate, phosphate and proteins) Factors affecting the growth of oral microorganisms Temperature  Usually about 37°C: favorable for mesophilic bacteria.  Big changes in seconds by consuming hot or cold foods  Bacteria unable to tolerate these changes decrease significantly in a transient manner. Oxygen Depends on:  Anatomical factors: gingival crevice, cracks interproximal areas of the teeth have less oxygen. and  Microbial factors: there are oxygen-consuming bacteria (Streptococcus, Neisseria etc.) that create a reducing atmosphere allowing anaerobes to develop (as spirochetes). Factors affecting the growth of oral microorganisms d. Adhesion, aggregation and co-aggregation factors: To avoid being eliminated by cleaning mechanisms (swallowing, saliva flow, hygiene, shedding...) microorganisms have developed different strategies: • Adhesion: interrelationships between organisms and tissues. Allows colonization (essential pre-requisite) • Aggregation: accumulation of bacteria from the same species forming clusters that stabilize colonization. • Co-aggregation: clumps of bacteria from different species. Allows colonization of bacteria that are not capable of adhesion. Factors affecting the growth of oral microorganisms For ADHERENCE, bacteria use:  Bacterial elements: adhesins whose function is to attach an organism to a tissue.  Receptors:  Where the adhesins settle  Ex. pellicle, glycocalyx carbohydrates  Fibronectin is very important as a receptor in epithelial surfaces (mucous) Factors affecting the growth of oral microorganisms Mechanisms of adhesion, aggregation and co-aggregation: 1. Lectin-carbohydrate binding: • Surface proteins of some bacteria (lectins) bind to carbohydrates placed on the pellicle (adhesion) or other bacteria (coaggregation). • There is a complementary effect between lectins and carbohydrates (as the Ag-Ab binding). • E.g. S. mutans and S. sanguis. 2. Protein-protein binding: • For the adhesion of bacteria to an acquired pellicle or for co-aggregation Factors affecting the growth of oral microorganisms 3. Glucans mediated binding: They are usefull for adherence to hard surfaces (enamel, cement ...) This type of binding involves:  Nonsoluble glucans  Surface proteins which bind to glucans  Glucosyltransferases (GTF) S. mutans has these 3 factors 1. GTF synthesize glucans and may be attached to the surface of the bacteria or excreted, remaining in the surrounding medium. 2. GTF, glucans and surface proteins that bind to glucans generate a network. 3. This network binds to the enamel acquired pellicle. Factors affecting the growth of oral microorganisms 4. Lipoteichoic acid binding: • Allow adherence to hard surfaces 5. Retention: • Not acts exactly as a mechanism of adhesion • Accumulation or mechanical retention in pits, fissures, interproximal areas, gingival sulcus, around prostheses and restorative materials. Factors affecting the growth of oral microorganisms e. Nutritional factors Bacteria obtain their nutrients from: 1. endogenous sources 2. interbacterial sources 3. exogenous sources 1. Endogenous sources (from host tissues and secretions).  Saliva: low nutrient content. Contains: • Carbohydrates in small amounts (derived from diet) and salivary glycoproteins (from the degradation by bacteria). • Free amino acids: in small quantities. • Proteins and glycoproteins: in large quantities. • Inorganic compounds: calcium and phosphates. Sodium ions, potassium ... Factors affecting the growth of oral microorganisms  Gingival fluid • Comes from the blood capillaries. When the amount of plaque is important or there is periodontal disease the amount of gingival fluid is greater. • Contains many nutrients such as:  Albumin  Glycoproteins and lipoproteins  Hemin  Ions: sodium, potassium, magnesium, calcium....  Conjunctival and epithelial cells They get released by desquamation of mucosal surfaces and its disintegration are nutrients for bacteria. Factors affecting the growth of oral microorganisms 2. Interbacterial sources:  Degradation of complex molecules: • Salivary glycoproteins • Extracellular polysaccharides • Intracellular polysaccharides • Capsules • Proteins from saliva or tissues • Amino acids  Excretion of products • Short chain fatty acids produced by anaerobes (Porphyromonas, Prevotella, Fusobacterium ....) are used by treponemes. • CO2 for the development of capnophilic bacteria • Degradation of amino acids produce ammonia which is used by S. mutans • Lactate: produced by streptococci and used by Veillonella. Factors affecting the growth of oral microorganisms 3. Exogenous sources (diet): • Short time of permanence inside the mouth (chewing, saliva flow) • Frequent intakes or adherent food • Macromolecules • The food does not reach all areas (gingival sulcus) • The most important nutrients that come from the diet are carbohydrates.  Bacteria can use carbohydrates to produce reserve polysaccharides  Bacteria can produce acids from carbohydrate. SUCROSE Factors affecting the growth of oral microorganisms f. Host protective factors  Mucose integrity  Cell desquamation (shedding) • Mechanical factor that limits the buildup of microorganisms • Does not work on the tooth surface or plaque attached to surfaces  Chewing and swallowing: Mechanical drag of microorganisms in the digestive tract. Factors affecting the growth of oral microorganisms  Lymphoid tissue • Extraoral nodes (submaxillary, submandibular, cervical mucus drain ...) • Intraoral lymphoid tissue: tonsils • Gingival lymphoid tissue • Salivary gland tissue: secret mainly IgA • Submucosal lymphoid tissue Factors affecting the growth of oral microorganisms  Saliva Mechanical drag due to the continuous salivary flow and muscle activation of the tongue, lips and cheeks. Drag due to swallowing saliva. • Contains clotting factors: rapid repair of erosions • pH buffer • Remineralizing power: saturated with calcium and phosphate. • Bacteria inhibiting factors:  Lysozyme: damages the peptidoglycan  Lactoferrin: captures iron, decreasing the amount of iron that is available for bacterial growth • Immune action:  Ig: the more abundant is IgA which blocks the binding of bacteria to cells  Complement  Leukocytes Factors affecting the growth of oral microorganisms  Gingival fluid: • Immunoglobulins: IgG predominates. When periodontitis is present, then IgG and IgM increase. • Complement: can be activated and participate in the development of lesions related with periodontitis. • Cells: neutrophils are the main type Factors affecting the growth of oral microorganisms g. Antagonistic factors between bacteria • Competition for nutrients: o Advantage for bacteria with better enzymatic endowment o Advantage for bacteria adapted to small amounts of nutrients • Hydrogen peroxide production • Oxygen consumption • Acid production • Bacteriocins Benefits of the oral microbiota • Synthesis of vitamins (vitamin K, biotin ...) • Bacterial enzymes that aid digestion • Avoid unusual growth of microorganisms or pathogens in the mouth (competition for nutrients, bacteriocins ...) COMPOSITION OF ORAL MICROBIOTA • It is very complex • 700 species identified • Up to 200 species in the same mouth in the course of time • Most of them are transients, about 20 are resident Gram positive cocci: Streptococcus viridans are the most isolated (qualitative and quantitative) Other species: Staphylococcus, Enterococcus, Abiotrophia, Peptostreptococcus (anaerobes) Composition of oral microbiota Gram-negative cocci Veillonella (anaerobe) and Neisseria species Gram-positive bacilli • Actinomyces and Lactobacillus species • Rothia dentocariosa • Corynebacterium "diphtheroids" matruchotii and other • Other anaerobes: Propionibacterium, Eubacterium and Bifidobacterium Composition of oral microbiota Gram-negative bacilli • Anaerobic species of Porphyromonas, Prevotella, Fusobacterium, Selenomonas and Leptotrichia bucalis • Facultative anaerobes: Aggregatibacter actinomycetemcomitans, Eikenella corrodens, and Haemophilus species, Capnocytophaga, ... Others • Fungi: Candida species • Mycoplasma • Parasites: Trichomonas tenax and Entamoeba gingivalis ORAL MICROBIOTA REPLACEMENT Replacement of some microorganisms by others in response to changes affecting the characteristics of where they live • Allogenic succession: the replacement of habitat changes due to non-microbial factors: birth, adulthood, tooth decay, use of prostheses and other artificial materials • Autogenic succession: the replacement in the microbiota by changes in the habitat due to microbial factors ORAL MICROBIOTA REPLACEMENT • Before birth (in utero): No microorganisms • Birth: acquisition of mother vaginal tract microorganisms (Lactobacillus, corynebacteria, gram negative bacilli: pioneer community) • Breastfeeding: Streptococcus salivarius group • 6 months: primary dentition (microbiota changes) • After the permanent dentition: climax community. The quantity and quality of microorganisms vary over the lifetime by ecological succession THANKS FOR YOUR KIND ATTENTION