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21 Cards in this Set
- Front
- Back
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What fluctuating conditions in the oral cavity influence microbial colonization?
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- Temperature
- Oxygen availability - pH - Nutrients (through dietary intake) - Fluid flow and dilution (saliva) - Unique innate and adaptive responses. |
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Define dental plaque and describe the developmental states in forming dental plaque, including what a microbe must do in order to establish dental plaque.
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Dental plaque is a tightly adherent film that forms on the teeth and is composed of bacteria and their extracellular polysaccharide (capsule).
Aerobic bacteria adhere to the tooth surface The aerobes actively eat sugars and respire, thus using lots of O2; the micro-environment becomes more anaerobic. Biofilm forms and bacteria start to perform anaerobic metabolism- fermentation. This produces lactic acid and promotes the growth of lactobacilli, which results in even more acidic conditions. Acids produced by plaque bacteria dissolve calcium phosphate minerals of the tooth. |
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Define gingivitis and calculus and list 3 species associated with plaque
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Gingivitis: is the inflammation of the epithelial and connective tissue that surrounds the teeth, but does not involve loss of connective attachment of alveolar bone supporting the tooth.
Streptococci Actinomyces Bacteriodes |
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3 species associated with plaque:
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Streptococci
Actinomyces Bacteroides |
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Name the 2 general approaches used to identify and classify oral microbes.
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Diagnostic and taxonomic approach
molecular approaches |
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Name 3 ways to perform sampling in the oral cavity and discuss the utility of each.
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Chewing paraffin: enables the enrichment of saliva for tooth-derived microbes
Using a sterile tongue blade: for collecting bacterial sample from the tongue Studying dental plaques directly: most representative samples for site specific study |
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Define 4 classes of media used in the culture of microbes
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Non- selective nutritive (Peptone, Tryptone, Mueller- Hinton).
Non- selective Enriched ( Brain-Heart, Blood, Serum, Egg, Vitamins, Minerals) Selective (Antibiotics, Dyes, Bile Salts, MacConkey) Differential (Metabolic Substrates, Mannitol Salt, MacConkey). |
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Compare and contrast the oxygen requirements for different types of microbes.
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Most oral bacteria are facultative anaerobes (with or without oxygen)
Strict anaerobe (cannot tolerate any oxygen) Microaerophilic anaerobes (require low levels of oxygen) Capnophilic bacteria (require CO2) |
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Describe 2 ways in which to identify cultured oral microbes.
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Morphology: size, shape, organization and colour both microscopically (using stains such as gram stain) and on agar (colonial morphology).
Biochemical: ability to ferment sugars, and the presence of particular enzymes. |
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State the utility of the gram stain in diagnostic oral microbiology.
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Allows colourless bacteria to be visualized in clinical samples
But not useful for some bacteria such as Mycobacteria and Spirochetes. This allows preliminary identification and therapeutic choices to be made prior to culture. Reports on gram stain include morphology, stain characteristics, also host cells and association between bacteria and host cells |
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Describe the 16S gene of bacteria and discuss why it is important for oral microbial taxonomy.
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The ribosomal 16S gene:
Ribosomes are the machinery that translate DNA sequence into proteins using the universal genetic code. The 16S gene encodes the RNA present in the small subunit of ribosomes. This translation function is so essential that the 16S genes are highly conserved between similar organisms within a species, and therefore, can be used for intra- and inter- species comparisons. |
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State 4 advantages of PCR for the identification of oral microbes.
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does not require culture
sensitive: allows the detection of very small numbers of oral microbes. Specific Rapid Inexpensive Can be made semi- quantitative by using real-time RT-PCR to monitor levels of microbes. |
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State what is meant by auxotrophic in relation to oral microbes.
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Auxotrophy is the inability of an organism to synthesize a particular organic compound required for its growth (as defined by IUPAC)
Oral microbes derive these nutrients from the host, either from saliva or dietary intake. |
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Define the bases of acid tolerance.
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Oral microbes have multiple mechanisms to cope with sudden drops in pH and sustained acidification. These traits favor the growth of aciduric, cariogenic plaque-forming oral microbes.
Use of Arginine Deiminase System to buffer themselves against pH drops via the production of ammonia from arginine 2. Use of Strickland reaction (fermentation of amino acids) 3. Pumping protons to maintain cytoplasmic pH that is neutral relative to outside (e.g. production of ammonia by arginine deiminase) and adaptive acid tolerance is critical for surviving low pH. |
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Describe what is meant by adaptive acid tolerance (AAT).
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Oral microbes can respond to acidification adaptively, which is related to the activity of F-ATPase.
Higher F-ATPase activity, and therefore more capacity to pump protons out of the cytoplasm, reduces internal acidification during glycolysis and is the basis of acidification adaptive responses. These changes enhance the capacity of oral microbes to produce acid at low pH, which increases their cariogenic potential. Continued acid challenge in the mouth (e.g. snacking on sugar foods) therefore, not only selects for more acid tolerant bacteria in plaque, but also enhances the caries producing potential of the organism by introducing adaptive acid tolerance. Adaptive acid tolerance is globally regulated in that many genes are induced and repressed in response to acidic conditions. Often adaptive acid tolerance develops with increased tolerance to other stress factors, such as oxidative stress (e.g. peroxides). Acid adaption is also correlated with increased levels of long chain fatty acids in membranes. In other words adaptive acid tolerance is a complicated response involving global regulators, multiple genes, multiple proteins and lipids. |
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Explain why a diet high in sugar has more than one affect on development of caries.
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1. The bacteria in the plaque ferment sugars to produce lactic acid, which causes demineralization of the tooth leading to dental caries
2. S. mutans use sucrose to form sticky polysaccharide. Many other sugars (e.g. glucose, fructose, lactose) are catabolised by S. mutans, where lactic acid is an end product. 3. Continued acid challenge in the mouth (e.g. snacking on sugar foods), not only selects for more acid tolerant bacteria in plaque, but also enhances the caries producing potential of the organisms by inducing adaptive acid tolerance. |
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State why respiration in oral microbes presents a mutagenic challenge.
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Metabolism of O2 by both aerobes and anaerobes can result in the production of toxic Reactive Oxygen Species (ROS) such as hydrogen peroxide (H2O2), superoxide radicals and hydroxyl and perhydroxyl radicals.
ROS can damage proteins and nucleic acid in bacteria |
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Describe the mechanism of action of fluoride.
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Fluoride is concentrated in plaque at levels 100 times greater than levels in saliva.
Fluoride is weakly acidic, and so moves into bacterial cells because of the pH across the cells membrane, with the cytoplasm alkaline relative to the environment. The primary action of fluoride is to dissipate the proton gradient (pH out << pH in) by carrying protons into the cell as HF at low plaque pH values. Other weak acids also concentrate in plaque biofilms including anti-0inflammatory reagents such as ibuprofen. |
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State the 2 mechanisms of gene transfer in oral microbes.
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The mechanisms responsible for horizontal gene transfer are:
Transformation; uptake of naked DNA by competent recipient cells, Conjugation; transfer of DNA through cell-cell contact, Transduction; introduction of DNA into a bacterial cell by a bacteriophage containing either random (generalized transduction), or specific (specialized transduction) pieces of DNA from the previous host. Evidence is limited in oral microbes. |
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Define transformation and competence.
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Transformation:
Transformation; uptake of naked DNA by competent recipient cells, Competence: (Is the ability of bacteria to uptake DNA by transformation) |
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Briefly describe why transposons are useful for study of oral microbes.
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Insertion of transposons is usually a random event and independent of extensive homology.
Therefore, transposons are used as a technique for mutagenesis in oral bacteria. |
