Microbiology of dental caries Flashcards
What things in the oral environment are relevant to caries?
-Tooth surface
- around 700 species of bacteria
- Saliva
- Gingival crevicular fluid
- Periodic availability of nutrients from host diet
what factors are required for the development of dental caries?
- teeth
-time
-bacteria in plaque
-Fermentable carbohydrate in diet
Are some bacteria more important than others in caries
- Clarke (1924) grew Streptococcus mutans from advanced carious lesions
- 1960s – organisms responsible for “infectious” dental caries in rodent models identified as member of mutans streptococci (MS) group and lactobacilli
- MS in humans – S. mutans and S. sobrinus. Other mammals have their own version, e.g. S. rattus in rats; S. cricetus in hamsters
Evidence implicating
Streptococcus mutans in caries
Streptococcus mutans found in high numbers in carious lesions
Subjects with active caries have higher salivary counts of S. mutans (>106/ml) than subjects without active caries (<103/ml)
What features of S. mutans makes it easier for it to survive?
It’s acidogenic & aciduric- produces high levels of acid & can survive & flourish in low pH conditions
What virulence factors are present in S. mutans that may enable it to contribute to the caries process?
-Produces Antigen I/II so adherence to surfaces
-Glucosyl transferases- produce glucan polymers from sucrose
-Glucan binding proteins- attachment of cells to glucans
Have any vaccines been developed for these virulence factors of s.mutans?
Vaccines have been developed (active and passive) against all three factors but no commercial vaccine yet available
is lactobacillus associated with caries?
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.
What kind of organism is lactobacillus?
It appears to be an opportunist organism that requires a low pH habitat so lactobacilli don’t initiate caries but will colonise existing lesions.
Doesn’t only appear in the mouth but also in the body and fermented food e.g yogurt
slide 8
what kind of bacteria is veillonella
Gram negative anaerobic cocci that is associated with caries.
Describe the importance of Veillonella in caries.
-Requires lactate as substrate for growth
-Lactate is produced by both streptococci and lactobacilli
-May be present in carious lesions because high levels of lactate are present.
-It has been suggested that veillonella may be beneficial to caries by reducing lactate levels but little evidence to support this.
What was the consensus reached about the microbiology of caries from recent culture & DNA-based studies?
-There’s a complex bacterial community in carious lesions
-S. mutans is frequently not present
-Some samples from caries-free sites have high levels of S.
mutans
Other acidogenic species are significantly associated with carious lesions, including Scardovia wiggsiae, lactobacilli etc.
What laboratory experiment did Bradshaw & Marsh carry out which forms the basis of much of our current thinking about the role of bacteria in caries?
-9 oral bacteria species growing together
-Glucose pulsed into them for 10 days.
-Fall in pH seen
-Increase in s.mutans and lactobacillus
-If pH was held at 7, no change in microbiota
Therefore, change in microbiota was in response to change in environment and not its cause
What is the extended ecological plaque hypothesis (Takahashi & Nyved 2008)?
Dynamic stability stage: associated with health; only mild or infrequent acidification
Acidogenic stage: arises if there is frequent/moderate acidification
Aciduric stage: so much carbohydrate is being consumed so regularly that the pH of the whole mouth falls.
look at slide 14 and 15
What was the background information that Takahashi & Nyved used to form their plaque hypothesis?
-S. mutans and lactobacilli are highly aciduric
-Mutans streptococci only a minor component of healthy plaque
look at slide 14 and 15
Describe the dynamic stability stage.
1.Acid produced from sugars by range of bacteria lowers pH of plaque
2.Followed by alkalinisation phase, caused by:
-diffusion of acid
-buffering by plaque constituents and saliva
-production of alkali by bacteria
- Production of alkali:
-ureolysis – ammonia production from urea by urease and reduction of nitrate
-arginine deiminase – dietary arginine catabolised to ammonia
Describe the acidogenic stage.
1.Initiated by:
-Repeated, raised levels of sugar intake
-Reduced salivary flow
-Poor oral hygiene
- Microbiota typically dominated by non-mutans streptococci and Actinomyces
Describe the aciduric stage.
- Occurs 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 Bifidobacterium and Propionibacterium species - 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