PMI02-2016 Microbiology of dental caries Flashcards
What are the four factors required for the development of caries?
Tooth surface
Time
fermentable carbohydrates in the diet
Bacteria in plaque
What is the evidence implicating streptococcus mutans in caries?
There are high numbers of streptococcus mutans in carious lesions
Patients with active caries have higher counts of s. mutans in saliva than subjects without caries
S. mutans is acidogenic and aciduric so produces high levels of acid and can survive and flourish in low pH conditions
What are the virulence factors of s. mutans?
Antigen I/II which enables adherence to surfaces
Produces glucosyl transferases which produces glucan polymers from sucrose
Produces glucan binding proteins which causes attachment of cells to glucans
How is lactobacillus associated with caries?
Low levels in individuals without caries
Require a low pH habitat , so lactobacilli do not initiate caries but will colonise existing lesions
What do veillonella require as a substrate for growth?
lactate produced by streptococcus and lactobacilli
How may veillonella be beneficial to caries?
Reduced lactate levels but there is little evidence to support this as lactate leads to demineralisation of the tooth
What is the consensus from recent studies about s.mutans?
S. mutans frequently not present, some samples from caries-free sites have high levels of s. mutans
What does an alkaline pH lead to?
Plaque and calculus formation
What does an acidic pH lead to?
Caries formation
What bacteria is found in white spot lesions?
Some mutans streptococci found
Lesions can form without MS
What bacteria is found in cavitated lesions in dentine?
Often dominated by MS and lactobacilli
What is the dynamic stability stage?
A small amount of fermentable carbohydrate eaten with a meal and nothing again until the next meal
There is mild/ infrequent acidification
What is the acidogenic stage?
Consuming fermentable carbohydrates between meals or in large amounts
There is moderate/ frequent acidification
What is the aciduric stage?
So much and regular consumption of carbohydrates
Causing pH to fall
Severe/ prolonged acidification
What stage has a net mineral gain?
Dynamic stability stage
Why does the alkanisation phase follow the dynamic stability stage?
Diffusion of acid
Buffering by plaque constituents and saliva
Production of alkali by saliva
What two processes constitute to the production of alkali?
Ureolysis: ammonia production from urea by urease and reduction of nitrate
Arginine deiminase: dietary arginine catabolised to ammonia
What bacteria are present during acidogenic stage?
non-mutant streptococci and actinomyces
What bacteria is present during aciduric stage?
S.mutans and lactobacili
When is root caries common?
When there is a lot of plaque on the root surface
What bacteria is found in root caries?
S. mutans and lactobacilli in root caries lesions with actinomyces species and bifidobacteria
What is the function of a-amylase in saliva with regards to plaque and caries?
Hydrolyses starch to glucose and maltose, so it is available for fermentation
It binds with high affinity to oral streptococci and retain activity when bound
Involved in bacterial adherence to pellicle
What is the purpose of sugar transport and entry into glycolysis for plaque and caries?
Sugars can be derived from host diet or salivary components
Sugars are transported to the interior of the cell
Sugars enter glycolysis
All sugars eventually give rise to pyruvate, which is a key metabolite intermediate
What is the phosphotransferase system?
PTS is a distinct method used by bacteria for sugar uptake where the source of energy is phosphoenolpyruvate
It involves enzymes of the plasma membrane and cytoplasm
The last stage in glycolysis powers the uptake of glucose in bacteria
