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Questions and Answers
Which factor influences the diversity of the oral microbiome in infants?
What is the first hard surface that allows for microbial colonization in a child's mouth?
What role does microbial antagonism play in the oral microbiome?
Which of the following is NOT a factor that influences an individual’s oral microbiome composition?
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During what period does the oral microbiome begin to establish itself in infants?
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What is the main characteristic of the human mouth that allows for a diverse microbial environment?
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What percentage of the oral microbiome's identified species are validly named culturable species?
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What is the initial process that leads to the formation of biofilms on teeth?
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Which of the following is a source of nutrients for the developing biofilm community?
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How do primary feeders in a biofilm contribute to the survival of secondary feeders?
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What role do membrane vesicles play in gram-negative bacteria within a biofilm?
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What is the consequence of quorum sensing regulation in bacterial populations?
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In a healthy oral microbiome, what is the primary waste product produced when certain bacteria ferment glucose?
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What is the result of antibiotic resistance gene acquisition in a biofilm?
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What is oral dysbiosis and its impact on oral health?
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What type of systems facilitate quorum sensing in gram-positive bacteria?
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What role do members of the biofilm community play in metabolizing lactic acid?
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What happens to the pH of the biofilm as a result of lactic acid metabolism?
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What occurs in dysbiosis regarding the composition of the biofilm community?
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How does the inflammatory response in healthy individuals differ from that in dysbiotic situations?
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What is GCF and what does it deliver during an inflammatory response?
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What is a potential negative consequence of the increased flow of GCF in patients with chronic dysbiosis?
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What systemic health issue can be triggered by periodontal disease according to the content?
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Which of the following statements about the relationship between lactic acid and tooth decay is true?
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Which of the following best describes hemin's role in biofilm development?
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Study Notes
The Oral Microbiome
- The human mouth houses the second most diverse microbial population after the gastrointestinal tract.
- Over 700 species have been identified, with 54% culturable and 32% detected through metagenome analysis.
- The oral microbiome has coevolved with humans and generally maintains a mutualistic relationship.
- Acquisition of the oral microbiome begins at birth, influenced by birth mode (vaginal or Cesarean) and infant feeding method (breastfeeding or formula).
- The composition of the oral microbiome changes with the eruption of baby teeth and again when they are replaced by adult teeth.
- The oral cavity is diverse with various microenvironments, including acidic, aerobic, anaerobic, and nutrient-rich zones.
- Factors influencing individual oral microbiome composition include hormones, tobacco use, sugar consumption, acidic drinks, stress, and oral hygiene practices.
Oral Biofilm Formation
- Biofilm communities in the oral cavity comprise both harmless and pathogenic members.
- Bacteria adhere to enamel surfaces coated with the acquired enamel pellicle through adhesins.
- Co-adhesion between organisms promotes colonization and biofilm formation on teeth.
- Biofilm formation is initiated through quorum sensing mechanisms involving two-component systems in gram-positive bacteria and the luxS-encoded autoinducer-2 (Al-2) systems in both gram-positive and gram-negative bacteria.
- The biofilm matrix, comprised of extracellular polymeric substances (EPS), provides carbon and energy for the developing population.
- Other nutrient sources include host proteins, salivary glycoproteins, and gingival crevicular fluid (GCF).
- Biofilm colonization order is influenced by the metabolic capabilities and nutrient requirements of individual species.
- Metabolism by primary feeders often provides nutrients for secondary feeders, leading to efficient nutrient utilization within the community.
Biofilm Horizontal Gene Transfer
- Quorum sensing regulation via two-component systems often promotes genetic competence within biofilms.
- The biofilm provides an ideal environment for horizontal gene transfer (HGT), including transformation, transduction, and conjugation.
- Membrane vesicles facilitate DNA transfer in gram-negative bacteria.
- The biofilm metagenome allows organisms to acquire genes, enhancing adaptation to changing environments.
- Antibiotic-resistance genes (ARGs) are prevalent within the oral cavity, providing a survival advantage to antibiotic-susceptible organisms.
Oral Dysbiosis
- Negative shifts in the oral microbiome can lead to oral dysbiosis, manifesting as dental caries and periodontitis.
- Consumption of dietary sugar contributes to dental caries.
- In healthy individuals, oral biofilms ferment glucose, producing lactic acid, which is then metabolized by other members, preventing its accumulation and maintaining a weakly acidic pH, minimizing enamel decay.
- Dysbiosis allows for the accumulation of lactic acid, leading to shifts in the biofilm community and favoring saccharolytic, acidogenic, and acid-tolerant bacteria.
- This reduces microbial diversity and beneficial activities within the biofilm, promoting enamel decay.
- Periodontitis occurs when chronic inflammatory responses are exaggerated due to microbial accumulation around the gingival margin.
- In dysbiosis, inflammation leads to increased GCF production, which contains substrates for proteolytic bacteria, including hemin, a nutrient essential for growth by potentially pathogenic species.
- Changes in microbial composition and competitiveness within the biofilm contribute to periodontal disease.
- Periodontitis is associated with bacteremia, facilitating the spread of bacteria from the oral mucosa to other parts of the body.
- Systemic spread of bacteria from periodontal disease may contribute to cardiovascular disease, rheumatoid arthritis, stroke, inflammatory bowel disease, respiratory tract infections, appendicitis, pneumonia, and diabetes.
Laboratory Experiment
- The experiment aims to examine the diversity and composition of oral biofilms on teeth and toothbrushes.
- Oral microbiome samples will be collected, diluted, and plated on selective and differential media to identify various groups and genera of biofilm communities.
- Tryptic soy agar with 5% sheep blood (blood agar) is a general, nonselective medium used for cultivation of various microbes, providing a source of hemin and allowing detection of hemolysins.
- Columbia CNA with 5% sheep blood agar, mannitol salt agar (MSA), and MacConkey agar are selective and differential media, described in detail in Exercise 18.
- Sabouraud's dextrose agar (SDA) is used to isolate yeasts from dental biofilms.
- Pseudocel agar (Cetrimide agar) is a selective medium for isolating and identifying Pseudomonas aeruginosa.
- Cetrimide inhibits the growth of most bacteria while enhancing the production of pyocyanin, a blue-green pigment, making P. aeruginosa colonies easily identifiable on this medium.
- Wilkins-Chalgren agar is a nonselective medium for cultivating clinically relevant anaerobic bacteria. It provides essential vitamins, growth factors, and substrates for anaerobic species.
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Description
Explore the complex ecosystem of the oral microbiome, focusing on its diversity, development, and the factors influencing its composition. This quiz covers key aspects of biofilm formation in the oral cavity and the implications for oral health. Test your knowledge about the interactions between microbial populations and human health.
