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82 Cards in this Set
- Front
- Back
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Biofilm
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a sophisticated microbial community with novel control mechanisms that determine biofilm architecture, microbial physiology and metabolism and survival. DENTAL PLAQUE is a biofilm
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Are biofilms always symbiotic?
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Microbial actions within the biofilm are not always symbiotic, since residents often must eliminate neighboring cells and even their own species in order to function optimally.
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Detachment
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there are programmed mechanisms for eventual detachment of residents from a biofilm which appears to be a survival mechanism permitting dissemination of inhabitants to more favorable environments.
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What is the basic structural unit of the biofilm
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the microcolony
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microcolony
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comprised of single bacterial species or a mixture of species. Close proximity of cells within the microcolony provides an ideal environment for creation of nutrient gradients, exchange of genes, and quorum sensing
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Distribution of Microcolonies
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not randomly distributed within the complete biofilm but are functionally and spatially organized into it.
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biofilm’s morphological appearance
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open mushroom-shaped structures which contain many channels. Nutrients, communication molecules, DNA, fluids and waste products can traverse through these for the benefit of the biofilm.
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4 Survival advantages of a biofilm
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1) Broader opportunities for OPTIMAL CELL FUNCTION. 2) Cooperative nutrient acquisition and METABOLISM, eg. different species participate in catabolism (breaking down) of large complex molecules to provide nutrients. 3) PROTECTION from antimicrobial agents and environmental stressors, eg. low pH or oxygen. 4) COLONIzATION RESISTANCE is a phenomenon whereby the biofilm discourages colonization by deleterious internal or external microorganisms.
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6 Biofilm activities
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1) Quorum sensing, 2) Chemical gradients, 3) Gene regulation and expression, 4) Interbacterial matrix, 5) Bacteriocin production, 6) Resistance to antimicrobial factors
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Quorum sensing
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a cell density directed inter-cell communication mechanism through which secreted protein molecules called pheromones or autoinducers regulate gene expression when an optimal cell density is achieved.
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What are the activities regulated by Quorem sensing?
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directs many of the basic activities of the biofilm, eg. nutrition, metabolism, resistance to environmental stressors and specific anti-microbials, biofilm maturity, detachment of residents and genetic regulation. This also regulates competency of residents to acquire new genes from other biofilm inhabitants.
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Chemical gradients
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Chemical gradients develop in biofilms which are crucial to microbial growth or survival (eg. nutrients, pH, oxygen, etc). These gradients are NOT linear. They are ARBITRARY. Such diversity allows fastidious bacteria to survive in any region of the biofilm, and enable microorganisms which would be incompatible with one another to co-exist. These systems also facilitate survival of oxygen-sensitive residents since bacteria which consume and detoxify oxygen are in close proximity to them, eg. facultative streptococci.
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Gene regulation and expression
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Genotypic and thus phenotypic changes accounts for many of the altered activities of the biofilm residents. These come about from UP- OR DOWN- REGULATION OF GENES BY ENVIRONMENTAL FACTORS, or GENE TRANSFER BETWEEN RESIDENTS.
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Horizontal gene transfer
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Occurs by transformation or conjugation and exchange of conjugative transposons or plasmids;
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What facilitates horizontal gene transfer?
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facilitated by the close proximity of the bacterial residents, and by quorum sensing molecules which enhance cell competency
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Cell competency
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ability to acquire external genetic material
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What genes are upregulated by attachment to a surface in faculative streptococci (eg. Strep. mutans)?
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up-regulates gene expression of exo-polymer formation, glycolysis and cell division.
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Interbacterial matrix
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As the biofilm matures, continued synthesis of EXOPOLYMERS (usually extracellular polysaccharides, ECP) occurs to form the main part of the extracellular matrix. Precipitated SALIVARY GLYCOPROTEINS also are present
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Functions of the matrix
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STRUCTURAL scaffolding,and is biologically active and can BIND or retain nutrients, water (thereby preventing desiccation) and key enzymes.
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Bacteriocin production
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Bacteriocins are proteinaceous toxins produced by bacteria which will inhibit the growth of similar or closely related bacterial strains. enables bacteria to select their neighbors, promote the establishment of single-species communities, destroy their own progeny to scavenge needed enzymes or DNA and ultimately play an important role in the balance and well-being of the oral ecosystem.
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Indigeneous microflora
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group of bacterial species which are able to colonize, survive, thrive and remain in an environment associated with a particular site after a suitable maturation period has transpired; Also quickly rebound after they are destroyed by antibiotic treatments. *its composition (the species present) will be similar to that of identical environments in another individual.
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Other names for indigeneous microflora
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resident, normal, commensal or conventional microfloras.
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What criteria must be met to be considered indigenous microflora
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Oral attachment (adhering to an oral surface); *”Oral surface” can also mean other attached microorganisms
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Transient microflora
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Bacteria in saliva are technically not considered as indigeneous, but as transients, even though most salivary bacteria are indigenous organisms which are shed into the saliva.
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Species of the oral indigenous microflora
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Roughly 95 to 98% is represented by only 20 to 30 species while the remaining 2 to 5% is made up of over 270+ species, most of which are not cultivable but have been identified by polymerase chain reactions (PCR).
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Consequences of environment changes
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Compositional changes where the same types of bacteria are present as normal but there will be a quamtitative change in composition (ex: proportional increase of Strep. mutans in a dental plaque which is frequently exposed to dietary sucrose)
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Microbial population shifts
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Proportional compositional changes are termed microbial population shifts; *Also called succession or enrichment. Keep in mind that species can also recede proportionally (called recession).
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Adherence
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ability to adhere (also termed attachment, adsorption or colonization) is a requirement of most bacterial species in an oral biofilm
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Pellicle
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thin film of glyoproteins derived from saliva
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Early microbial colonization of teeth (2 steps)
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1) precipitation of acquired enamel pellicle (pellicle) from saliva on teeth. 2) attachment of bacteria from saliva to the pellicle by REVERSIBLE binding interactions. *Later, if the bacteria possess BINDING SITES on their cell walls, fimbria or capsules which react specifically with appropriate RECEPTOR SITES on the designated surfaces (eg. pellicle or other attached bacteria), IRREVERSIBLE attachment takes place.
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Adhesins
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Binding and receptor molecules that are highly specific for each other. These may be proteins, carbohydrates, glycoproteins or lipids. Strength of attachment is determined by the number of adhesins on the bacterial surface.
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What happens to early colonizers that do not have adhesins?
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Early colonizers without specific binding/receptor sites will eventually be sheared off by oral forces.
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Which species dominate the biofilm after 12 hours of initial dental plaque development?
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facultative streptococci will dominate the biofilm, .Strep. sanguinis and Strep. oralis are the most numerous species.
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Late dental plaque development (beyond 12 hours)
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1) Gram positive genera like Actinomyces, and Gram negative genera like Veillonella appear and new streptococcal colonization diminishes. 2) The plaque environment becomes more anaerobic due to reduction of oxygen by metabolic activities of the early facultative residents - most subsequent arrivals are anaerobes and attach to early colonizers by adhesins on the terminal ends of their FIMBRIA. 3) After 3 to 5 days, the dental plaque environment becomes increasingly anaerobic which favors colonization by Gram negative obligate anaerobic rods such as Fusobacterium, Prevotella, Porphyromonas and spirochetes (Treponema species).
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Describe the nutrient environment of supra-gingival vs sub-gingival plaque
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1) SUPRAGINGIVAL: deficient in protein and high in sugars (from host-consumed dietary sugars and glycoproteins from saliva).* Dietary nitrogenous substrates (proteins) as well as complex carbohydrates, are not routinely metabolized by supragingival bacteria because they are cleared from the mouth before degradation 2) SUBGINGIVAL: deficient in sugars and high in proteins.
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Saccharolytic
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Organisms that metabolize sugars; Supragingival bacteria like streptocooci; Saccharolytic bacteria convert sugar to acid (primarily lactic) in order to generate ATP (GLYCOLYSIS).
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Glycolysis
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Converting sugar to acid (primarily lactic) in order to generate ATP
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Supragingival bacteria
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Gram+ and facultative bacteria
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What 2 species are the most saccharolytic in oral biofilm?
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streptococci and actinomyces; found in high numbers where sugar is frequently present. (supragingival)
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How do streptococci (and others) adapt to not having constant exposure to sugar?
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Since sugar exposure is periodic, they convert sugar to INTRACELLULAR POLYSACCHARIDE (ICP), a glycogen-like storage polymer which can be metabolized for ATP production when dietary sugar is scarce, with lactic acid as the by-product.
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What do streptococci (and others) make in a high-sugar environment?
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EXTRACELLULAR POLYSACCHARIDE (ECP) formation on cell walls of certain bacteria. synthesized from sucrose.
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Acidogenic species
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species which produce acid; Cause periodic FLUXUATIONS in the environmental pH; CARIOGENIC BIOFILMS
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Aciduric species
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species which tolerate a low pH; These also exist in high numbers in supragingival plaque
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Nutrients for Subgingival dental plaque
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come mainly from GINGIVAL CREVICE FLUID (GFC) which flows into the gingival crevice from the soft tissue. GFC is deficient in sugars and high in proteins. Composition similar to SERUM
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Subgingival bacteria
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Gram– , anaerobic
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Proteolytic / asaccharolytic
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Species that metabolize proteins and not sugars dominate SUBGINGIVAL environment
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Byproducts of proteolysis
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complex array of metabolic by-products, many of which contain NITROGEN such as ammonia, amines and indole, and tend to be ALKALINE (basic).
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Effects of proteolytic byproducts
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Most metabolic by-products are consumed as substrates by inhabitants of the plaque, but some are IMFLAMMATORY or elicit undesirable characteristics such as ORAL MALODOR caused by volatile SULFUR-containing by-products. *Subgingival bacteria are is responsible for most of the plaque-mediated diseases AFFECTING SOFT TISSUE
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Subgingival environment (2)
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1) a high environmental pH (BASIC pH 7.5 to 8.5) which tends not to fluctuate. 2) CALCULUS formation which only occurs at a pH above 7.0,
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pH optima
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All enzymes have an optimal pH range at which catalytic activity is maximal; Most enzymes will function at a slower rate outside of this range, but this may diminish the organism’s growth rate and competitiveness in the biofilm
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The pH optima of most vital enzymes in biological systems
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close to neutrality, which also is the cytoplasmic pH in most bacteria
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How do bacteria maintain internal pH neutrality?
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bacteria have membrane-associated enzymes which regulate intra-cellular protons (H+) by actively expelling or internalizing them when necessary.
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Which bacteria tend to have highly adapted proton pumps?
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cariogenic species (ie. lactobacilli, Strep. mutans and Candida albicans), which are aciduric (acid-loving) and can survive at low pHs. Pumps include F-ATPases like H+-translocating ATPase
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Which bacteria tend to have weak proton pumps?
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periodontal and endodontic pathogens such as PORPHYROMONAS; They cannot tolerate acidic environments and thrive when the pH is close to 8.0 or above.
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How does the HOST regulate pH in the oral environment?
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SALIVARY BUFFER SYSTEMS, esp. the bicarbonate system keeps pH close to neutral; Salivary sink effect also helps
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Salivary sink effect
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natural washing by moving salivary films clears away acidic by-products, among other substances, from oral biofilms.
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pH regulation by host-bacterial interaction
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Host produces ARGININE and UREA and sceretes them in saliva and gingival crevice fluid (GCF); Many plaque bacteria possess enzymes which metabolize ARGININE or UREA to produce AMMONIA which is a strong alkali (basic) that protects against acidity/dental caries.
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How can oxygen be lethal to bacteria?
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its high reactivity with electrons disrupts microbial metabolism.
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Electron sink
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OXYGEN INTERMEDIATES formed during the metabolism of O2 divert electrons away from other metabolic reactions.
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Creation of oxygen intermediates
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1) atmospheric oxygen is converted into water it accepts 4 protons (H+) accompanied by 4 electrons (e-), 2) Short-lived intermediates are made during this rxn that add 1 to 3 extra electrons onto the oxygen atoms.
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3 Oxygen intermediates created
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1) SUPEROXIDE (O2-,with 1 extra e-); 2) HYDROGEN PEROXIDE (H2O2, with 2 extra e-) and 3) HYDROXYL RADICAL (HO• radical with 3 extra e-).
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Reaction that creates hydroxyl radicals
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requires ferrous ions (Fe++) procured from lysed blood cells
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Toxicity of Hydroxyl radicals
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The hydroxyl radicals can react with a variety of cellular components, such as nucleic acids (DNA, RNA), proteins, lipids and membranes, and thereby cause substantial damage that ultimately kills the cell.
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Toxicity of Superoxide
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can oxidize sulfhydral groups forming disulfide bonds in vital enzymes which render them non-functional
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Toxicity of hydrogen peroxide
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hydrogen peroxide being uncharged, can penetrate cell membranes, disrupt vital enzymes and mutate DNA.
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Ranking of most to least toxic
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1) Hydroxyl radicals, 2) Hydrogen peroxide, 3) Superoxide
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How do cells and bacteria protect themselves from O2 intermediates?
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eliminate or destroy O2 intermediates via the enzymes SUPEROXIDE DISMUTASE (dismutes/transforms superoxide to O2 plus H2O2) and CATALASE (changes H2O2 to O2 and H2O); *With the exception of certain streptococci, most facultative species produce catalase).
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Detoxification of hydroxyl radicals
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occurs when superoxide and hydrogen peroxide are neutralized by superoxide dismutase/catalase AND ferrous ions are eliminated or rendered inert.
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How do organisms defend against toxicity by ferrous ions?
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most living organisms use and store iron in protein-bound forms.
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What kinds of bacteria do not synthesize oxygen-protective enzymes?
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OBLIGATE ANAEROBES generally do not synthesize oxygen-protective enzymes and are killed rapidly in the presence of oxygen intermediates.
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Facultative anaerobes
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Can tolerate oxygen since they synthesize oxygen-protective enzymes, but do not use oxygen for energy
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Aerobes and mammalian cells
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not only synthesize high levels of these enzymes but utilize oxygen to produce energy.
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Benefits of indigenous bacteria in non-pathogenic types of dental plaque
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protect the host against colonization and infections by external or internal pathogens (COLONIzATION RESISTANCE); Ex: protects against overgrowth of indigenous Candida species and counteracts cariogenesis or periopathogenesis by antagonism to oral pathogens, eg. HYDROGEN-PEROXIDE FORMERS inhibit periopathogens, and ALKALI-FORMERS neutralize acid from cariogenic bacteria like Strep. mutans
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What can cause Candida overgrowth?
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When the normal oral flora is reduced by antibiotics, candida may proliferate freely and cause inflammatory lesions.
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Opportunistic pathogens
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Oral pathogens are almost always indigenous species and thereby can be viewed as “opportunistic” pathogens and are non-pathogenic at low concentrations, but become pathogenic when numbers increase; Usually increase due to adverse environmental changes within the oral cavity.
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Non-specific plaque hypothesis
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Previous belief that Soft and hard tissue diseases of the mouth are due to “dental plaque” in general, not specific pathogens
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Specific plaque hypothesis
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Current theory that diseases are due to specific pathogens
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Specific ecology hypothesis
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pathogenicity and virulence of the oral pathogens are variable and may depend on factors elaborated by the host, neighboring bacteria within the biofilm or the environment; environment as a controlling factor; Says that plaque-mediated diseases should be considered as ecological disruptions of natural habitats (POLLUTION) causing succession of detrimental opportunistic microorganisms to emerge. Also says pathogenic strains arise from acquisition of DNA or molecular triggers in environment
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Based on specific-ecology hypothesis what is the best strategy against pathogenicity?
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maintenance of healthy biofilm environments by identifying and eliminating the pollutants is more effective than just simply eliminating microorganisms.
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Red complex
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Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia; periodontal pathogens
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Evidence of the Specific ecology hypothesis (5)
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1) ATTACHMENT TO A SURFACE AS ENVIRONMENTAL CHANGE: Up-regulation of glucan production and glycolysis by Strep. mutans occurs when contacting and adhering to a surface. Both traits are virulence mechanisms of cariogenic bacteria
2) PATHOGENICITY ISLANDS in virulent strains of periodontal pathogens such as PORPHYROMONAS GINGIVALIS (Pg) is evidence of horizontal gene transfer in plaque biofilms, and may explain why non-pathogenic Pg is sometimes in biofilms associated with healthy tissue. 3) CLONAL VARIANTS: can express survival traits in the presence of environmental stressors like oxygen or low pH. (ex: phenotypes such as cell surface adhesins to enhance colonization, new proteolytic activity or increased aciduricity and acidogenicity), 4) SYNERGISTIC ENHANCED VIRULENCE: certain combinations of oral bacterial species induce increased pathogenicity and tissue damage compared to each of the species tested singly. For example, the main periodontal pathogens, ie. Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia (called the RED COMPLEX as a group) produce only small abscesses in animals when introduced singly, but much larger ones when any combination of the three pathogens is employed. 5) ORAL POLLUTION: Factors such as diet, tobacco smoking, medications, emotional stress, and several others can obstruct the microbial or host defense equilibrium and tip the balance toward tissue disruption. |
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What are the predominant oral pollutants?
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non-abrasive, soft-consistency diets which lead to gingival inflammation and dietary sucrose which stimulates proliferation of cariogenic bacteria.
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