Theme II: Oral microorganisms & diseases (Part 1, 14-19) Flashcards
What terms are used to describe microbes that are always found at a particular site and ones present only transiently.
- Autochthonous microbes: characteristically found at a particular site - adapted to grow & survive there
- Allochthonous: passes transiently, for a short time - either just passing (eg. in saliva) or can colonise if the site is compromised.
What 2 main bacteria species are found on dry and on moist lips, and what happens hameolysis occurs when you kiss blood agar
- Staphylococcus on dry areas (no haemolysis - y-haemolysis)
- Streptococci on moist areas. Produce H2O2 which bleaches haemoglobin on blood agar plate (alpha-haemoglobin)
Process of plaque formation (also mention the main contents, the time it takes to build up and mature)
- Plaque starts to build up within minutes of brushing. Bacteria adhere to proteins in the enamel pellicle and accumulate to form dental plaque.
- Streptococci make up over half of bacteria in initial plaque. Most bacteria are attached to epithelial cells that have sloughed from soft tissues.
- Plaque reaches maximum thickness at 24 hours which feels fury. It takes 1-4 days to form mature plaque.
- Over time microbes within it change and start becoming more pathogenic.
Ways bacteria are removed from oral surfaces
- Sloughing of epithelial cells
- Mechanical debridement (brushing)
- Active release
Next generation sequencing techniques for bacteria (targeted and full sequencing)
- Targeted: analysing the 16S rRNA genes
- Full sequencing: conducting millions of different reactions simultaneously. The short sequences are then stitched together bioinformatically to obtain much longer sequences or, in many cases, a whole genome. This is a much quicker method than methods used before such as Sanger sequencing which was very slow
What is a bacteriophage and its role
A virus. It reduces levels of invading pathogens as breaks them down, but can also transfer genes between bacteria (transduction). Infects and replicates within bacteria
Definition of holobiont
- The host organism and all its symbiotic microbial residents (we benefit from microbes, and they benefit from us)
- We have evolved together and they play a huge role in our physiology and health, while they use our nutrients and favourable conditions to grow
Functions of saliva
- Aid in digestion
- Antimicrobial effects (lysozyme, defensins)
- Forms food bolus to make food easy to swallow
- Mineralisation (statherin, PRPs)
- Moistens and lubricates the mouth to help with speech and to protect mucous membranes (mucins)
- Buffering
- Washes away debris and bacteria
How bacteria bind to saliva and teeth. What is the pellicle, composition, its role, thickness
-Protein in bacteria interact with proteins in saliva to be removed (aggregation), or interact and adhere with proteins on oral surfaces (enamel pellicle or epithelium)
- Pellicle is a deposit of saliva proteins and glycoproteins on the surface of the tooth to which bacteria bind to and then accumulate to form dental plaque (bacteria does not attach directly to the teeth)
- Pellicle contains enzymes that protects the teeth from effects of bacteria (eg. lysozyme, peroxidase, carbonic anhydrase isotope VI)
- It acts as a lubricant to reduce tooth wear.
- Reduces mobility of calcium & phosphate ions, reducing demineralisation.
- Pellicle is not removed by brushing
- It is 1-3 um thick
- Pellicle contains same proteins in saliva but in different proportions.
Balance between bacteria aggregation and adhesion, in the saliva and pellicle. What proteins etc. are involved
- Some proteins exhibit different binding properties when in fluid phase and on surfaces.
- Aggregation: occurs in fluid phase. Components in saliva cause bacteria to clump which can then be removed by swallowing. (Immunoglobins, Mucin MG2, gp340 agglutinin (also present in pellicle).
- Adhesion: Proteins in saliva pellicle on surface of teeth bind to bacteria causing adhesion and colonisation. (gp340)
3 broad-spectrum antibacterial enzymes in saliva and their function. [these enzymes are also found in dental products]
- Lysozyme: breaks down peptidoglycan in cell wall, leading to cell death.
- Lactoperoxidase: converts H2O2 (a by-product of streptococci) into hypothiocyanous acid which is more toxic to all bacteria.
- Lactoferrin: binds iron and hides it making it unavailable for bacteria that need it to survive.
Differences between supra gingival and sub gingival plaque. (nutrients, types of bacteria, how many cells)
- Supragingival plaque: forms above the gumline. Most bacteria are aerobic and fed by nutrients in saliva/ food. Shift to acidogenic & aciduric bacteria which lead to caries. 10^11 cells.
- Subgingival: forms below the gumline, usually when periodontal pockets start to form. 10^3 to 10^6 cfg/crevice. Anaerobic bacteria that cannot be found elsewhere in the mouth, except tongue. Nutrients from gingival crevicular fluid. Asaccharolytic, proteolytic bacteria (can’t break down sugars but break down protein by making protease, as no sugars found here but proteins are)
5 salivary proteins in pellicle that act as receptors for bacteria to bind to
- MG1 mucin
- Amylase
- Proline-rich proteins
- Statherin
- gp340 (salivary agglutinin)
Factors that affect plaque accumulation
- Accumulation fastest during the day
- Amount of saliva and its components
- Adhesins in bacteria allowing it to bind
- Coaggregation
- Diet, smoking
- (Lots of sugar doesn’t affect the initial accumulation, has more of an affect once its built up when it selects for acid-producing bacteria. Amount of plaque doesn’t correlate with caries)
What do mucins MG1 and MG2 and where they are found.
- Mucins inhibit microbial attachement
- MG1: in pellicle inhibits s.mutans biofilm formation
- MG2: present in fluid phase binds to bacteria for removal
What is the role of antigen I/II in streptococci
- It is a large adhesion protein found on its surface.
- Mediates adhesion to gp340 in saliva (fluid phase & pellicle)
What are oral bacteria food webs
- Initial growth of plaque uses saliva nutrients
- but as plaque matures, there is nutrient exchange between organisms.
- Bacteria will utilise waste products from other species so the end products of metabolism can be recycled. For example, several bacteria can utilize lactate (Veillonella spp.)
What is dental calculus. Why it forms behind lower incisors mainly. and what are sialoliths
- Plaque hardens to become calculus if not removed.
- Caused by precipitation of minerals from saliva and gingival crevicular fluid. Precipitation kills cells but the hardened surface is ideal for further plaque formation. And triggers inflammation
- Calculus forms mostly near salivary duct openings where there is greater flow of minerals.
- Sialoliths: calcified minerals in salivary glands and ducts - supersaturated calcium phosphate
What are exopolysaccharides of the biofilm matrix and how are they synthesised. What are the insoluble and soluble fructans and glucans and the genes that make them. Which polysaccharide is plaque mostly made of (70%)
- EPS are polymeric carbohydrates made of monosaccharide units. Majority of the biofilm matrix is made of polysaccharides (glucans and fructans)
- They are made outside of the cell by bacteria, using sucrose as a substrate (because it has high energy bonds between the glucose & fructose)
- Insoluble Fructan= Inulin (B-2,1 bond) Ftf gene
- Soluble Fructan = Levans (B-2,6 bond) Ftf gene
- Insoluble Glucan = Mutan (a-1,3 bonds) GtfB gene
- Soluble Glucan = Dextran (a-1,6 linked) GfdD genes
-70% of plaque EPS is made of mutan.
Why are glucan and fructans so complex/ unusual
- Some enzymes can catalyse multiple types of bonds of in different types of glucan/ fructans (which is unusual for enzymes)
- They don’t need a primer
- As glucan is being built, the enzyme stays attached for a while then falls off and other enzymes can come in - semi-possessive reaction where multiple enzymes work on 1 polymer.
- Glucans are extracellular and secreted into a complex environment with many types of species secreting their own enzymes
Bacteria express genes that encode the enzymes involved in glucan and fructan formation. What 2 enzymes catalyse formation of glucans and fructans. And which genes are involved in which polysaccharide
-Glucosytransferase and fructosytransferase enzymes
- GtfB gene= produce insoluble Mutan (a glucan)
- GtfC = a branched partially soluble Mutan
- GtfD = soluble dextran (a glucan)
- Ftf = produce fructans (Inulin & Levans)
What is the pH of Mutan rich micro colonies and why
- Very low as traps hydrogen ions.
- This then has an impact on the carcinogenicity of the biofilm, as it helps in adhesion and acid production.
