Microbiology of dental caries Flashcards
What are the 4 factors needed to cause caries?
Tooth surface
Bacteria in plaque
Time
Fermentable carbohydrate in diet
How is the oral environment relevant to caries?
- Tooth surface
- Around 700 species of bacteria
- Saliva
- Gingival Crevicular fluid
- Periodic availability of nutrients from host diet
What bacteria in the past have been considered to be more important than others in caries?
- Clarke grew Streptococcus mutant from advanced carious lesion
- 1960s organisms responsible for infectious dental caries recognised as metans streptococci and lactobacilli
What evidence links Streptococcus mutans in caries?
- Streptococcus mutans found in high numbers in carious lesions
- Subjects with active caries have higher salivary counts of S.mutans than subjects without active caries
- S mutans acidogenic and aciduric - producing high levels of acid and can flourish in this environment
What are the virulence factors of strep mutans?
- Antigen 1/2 - adherence to surfaces
- Glucosyl transferases to produce gluten polymers from sucrose
- Glucan binding proteins - attachment of cells to glucans
Why can we not vaccinate against strep mutans currently?
Originally through active vaccines could be produced but problem as some streptococci have antigens that react with cardiac tissue so not possible to take the risk of the vaccine affecting this tissue.
Give some details on lactobacillus bacteria
- Earliest studies associated lactobacilli with caries
- Very low levels in individuals without caries
- Many different species found in caries and thought to be of equal importance
- Most oral bacteria are only found in the mouth but oral Lacktobacillus spices are found elsewhere in the body and in fermented foods e.g. yogurt
- Appear to be opportunist organisms that require low pH habitat
- Lactobacilli do not initiate caries but will colonise existing lesions
Veillonella are found in high quantities in caries.
Give some details on this bacteria
- Gram negative anaerobic cocci
- Associated with caries
- Requite lactate as substrate for growth
- Use lactate produced by streptococci and lactobacilli
- May present in carious lesions as high levels of lactate present
- Could be beneficial in caries as it will reduce lactate level and the lactate causes demineralisation
Caries in the microbiome era:
Give some explanation of this
Advances in DNA sequencing and analysis have transformed our understanding of the human-associated microbiota.
Each site in the body has its own characteristic microbiota.
Individuals have their own, relatively stable, characteristic microbiota which is far more diverse than previously realised.
What has been concluded about the microbiology of caries?
- Complex bacterial community in carious lesions
- S.mutans frequently not present
- Some samples form caries-free sites have high levels of S.mutans
What is the role of pH in caries ecology?
Laboratory model containing 9 oral bacteria species growing together.
Pulsed with glucose on 10 consecutive days - fall in pH and increase in S.mutans and Lactobacillus.
If pH was held at 7, no change in microbiota was seen.
Change in microbiota was response to change in environment, not its cause.
(Lab experiment:
9 bacterial species grown in continuers culture (free in nutrients and remove waste products)
Added glucose on 10 consecutive days. This causes a fall in pH and an increase in step nuts and lactobacillus.
In the next experiment, the pH was maintained at 7, there was no change in microbiota.
This shows that the change in microbiota was a response to change in environment.)
Give some background on extended ecological plaque hypothesis
Mutans Streptococci only minor component of healthy plaque and do not adhere well to teeth.
White spot lesions - some strep mutans found. Lesions can form without MS.
Cavitated lesions in dentine - often dominated by MS and lactobacilli.
S.mutans and other streptococci make acid from sugars and produce final pH of 4-5, below 5.5, necessary for demineralisation of enamel.
S.mutans and lactobacilli are highly acidic - able to grow and continue to produce acid at low pH.
(Lesions can form without strep mutans.
Sometimes there were no mutans in cavitated dentine lesions.
Found that many bacteria can lower acid below 5.5 so demineralisation of enamel starts.
The bacteria were highly aciduric)
Summarise the dynamic, acidogenic and aciduric stage during caries microbiology
Dynamic = only mild and infrequent acidification
Acidogenic = moderate or frequent acidification (snaking, large amounts of carbohydrate)
Aciduric = buffering capacity is broken down, pH of mouth falls, due to large number of carbs frequently)
Give lots of detail on the dynamic stability stage
- Acid produced from sugars by range of bacteria lowers pH of plaque
- Followed by alkalisation phase caused by:
Diffusion of acid
Buffering of plaque constituents and saliva
Production of alkali by bacteria - Production of alkali:
Ureolysis (ammonia production from urea by urease and reduction of nitrate)
Arginine deaminase (dietary arginine catabolised to ammonia)
Give details on the acidogenic stage
Initiated by:
- Repeated, raised levels of sugar intake
- Reduce salivary flow
- Poor oral hygiene
Microbiota typically dominated by non-mutant streptococci and Actinomyces.
(Repeated sugar intake and reduced salivary flow (dry mouth) and poor oral hygiene less to this.
Dry mouth - carbohydrate is not washed away in saliva and acid produced for a longer period.
Poor oral hygiene - increases amount of plaque present
Tends to be dominated by other bacteria that can produce acid but can’t tolerate acid conditions)
Give details on the aciduric stage
After prolonged acidogenic stage, the buffering capacity of saliva is lost and bacterial community changes with:
- Selection of aciduric bacteria, particularly S.mutans and lactobacilli and some others
Thus, the ecological change drives the change in the composition of the microbiota and not vice versa, but the presence of aciduric bacteria compounds the disease state.
(High level acid for a long period of time,
Erodes buffering capacity of saliva.
Acidiuric bacteria grow here e.g. strep mutan group)
Root caries?
Who is is more of a problem in?
Older people due to retaining teeth affected exposed roots.
Strong correlation with amount of plaque on root surface, reinforcing need for good oral hygiene.
Microbial analysis has found S.mutans and lactobacilli in root caries lesions.
What components of saliva are important in plaque and caries and give details on the most important?
Amylase Lysozyme IgA Phosphate Calcium
Amylase:
Hydrolyses starch into glucose and maltose, thus making it available for fermentation (simple sugars available to bacteria).
Binds with high affinity to oral streptococci and retains activity when bound. This may be evolutionary are strep mutant can obtain glucose by having amylase bound to their surface.
Involved in bacterial adherence to pellicle.
Give details on sugar transport into bacteria and entry into glycolysis
Sugars can be derived from host diet or salivary components e.g. sucrose, maltose.
sugars are transported to the interior of cell during the phosphotransferase system (PTS) and other systems.
Following transport, sugars enter glycolysis at different stages of the pathway.
All sugars eventually give rise to pyruvate, which is a key metabolic intermediate.
What are the 3 ways that sugars is available to bacteria?
Ways sugar is available to bacteria:
Present in diet
Broken down from starch
Derived from salivary glycoproteins
Give brief details on the glycolic pathway
Glucose is phophorylated with 2 molecules of ATP. This forms fructose,1,6,bisphosphate which is split into 2. These molecules are then dephosphorylated with the generation of 2 ATP molecules for each molecule.
Net gain of of 2 ATP molecules.
How does the phosphotransferase system work?
ATP made in glycolysis is used in this system for sugar transport.
Energy comes for the liberation of ATP when pyruvate is formed.
Glucose binds to transporter system in cell wall of bacterial cell. Phosphate is used to convert glucose and bring it into cell as glucose 6 phosphate.
Uptake of sugar is driven by glycolytic pathway itself.
What are the main products formed in glucose fermentation?
Lactate Propionate Butyrate Acetate Formate
These are are short chain simple sugars.
Is sucrose more important than other sugars?
There is a wide range of sugar transporters and metabolic pathways for acid production from sugars among oral bacteria.
Some bacteria have ability to form polymers from sucrose specifically.
