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PMI > PMI02-2016 Microbiology of dental caries > Flashcards

PMI02-2016 Microbiology of dental caries Flashcards

1
Q

What are the four factors required for the development of caries?

A

Tooth surface
Time
fermentable carbohydrates in the diet
Bacteria in plaque

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2
Q

What is the evidence implicating streptococcus mutans in caries?

A

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

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3
Q

What are the virulence factors of s. mutans?

A

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

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4
Q

How is lactobacillus associated with caries?

A

Low levels in individuals without caries

Require a low pH habitat , so lactobacilli do not initiate caries but will colonise existing lesions

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5
Q

What do veillonella require as a substrate for growth?

A

lactate produced by streptococcus and lactobacilli

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6
Q

How may veillonella be beneficial to caries?

A

Reduced lactate levels but there is little evidence to support this as lactate leads to demineralisation of the tooth

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7
Q

What is the consensus from recent studies about s.mutans?

A

S. mutans frequently not present, some samples from caries-free sites have high levels of s. mutans

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8
Q

What does an alkaline pH lead to?

A

Plaque and calculus formation

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9
Q

What does an acidic pH lead to?

A

Caries formation

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10
Q

What bacteria is found in white spot lesions?

A

Some mutans streptococci found

Lesions can form without MS

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11
Q

What bacteria is found in cavitated lesions in dentine?

A

Often dominated by MS and lactobacilli

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12
Q

What is the dynamic stability stage?

A

A small amount of fermentable carbohydrate eaten with a meal and nothing again until the next meal
There is mild/ infrequent acidification

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13
Q

What is the acidogenic stage?

A

Consuming fermentable carbohydrates between meals or in large amounts
There is moderate/ frequent acidification

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14
Q

What is the aciduric stage?

A

So much and regular consumption of carbohydrates
Causing pH to fall
Severe/ prolonged acidification

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15
Q

What stage has a net mineral gain?

A

Dynamic stability stage

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16
Q

Why does the alkanisation phase follow the dynamic stability stage?

A

Diffusion of acid
Buffering by plaque constituents and saliva
Production of alkali by saliva

17
Q

What two processes constitute to the production of alkali?

A

Ureolysis: ammonia production from urea by urease and reduction of nitrate
Arginine deiminase: dietary arginine catabolised to ammonia

18
Q

What bacteria are present during acidogenic stage?

A

non-mutant streptococci and actinomyces

19
Q

What bacteria is present during aciduric stage?

A

S.mutans and lactobacili

20
Q

When is root caries common?

A

When there is a lot of plaque on the root surface

21
Q

What bacteria is found in root caries?

A

S. mutans and lactobacilli in root caries lesions with actinomyces species and bifidobacteria

22
Q

What is the function of a-amylase in saliva with regards to plaque and caries?

A

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

23
Q

What is the purpose of sugar transport and entry into glycolysis for plaque and caries?

A

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

24
Q

What is the phosphotransferase system?

A

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

25
Q

What is the end desired product for acidogenic bacteria of pyruvate?

A

lactate

26
Q

What do bacteria in plaque metabolise sucrose into?

A

To synthesise extracellular polysaccharides which constitute the plaque matrix

27
Q

What are the purpose of EPS to the bacteria?

A

They are ‘sticky’ polymers and contribute to the adherence of bacteria to the pellicle and plaque
They make bacteria more resistant to being washed away
They can also be a source of sugars for metabolism and growth when nutrients are limited

28
Q

What are glucosyl transferases?

A

The enzymes that form EPS

29
Q

How many glucose transferases does S.mutans form?

A

3

30
Q

How is glucan synthesised?

A

Sucrose is made up of a fructose and glucose unit

Sucrose binds with a prying molecule which extends the polymer and liberates and fructose molecule

31
Q

How is fructan synthesised?

A

Sucrose binds with a priming molecules which extends the polymer and liberates a glucose molecule

32
Q

How is glucan hydrolysed?

A

Glucanase will combine the glucan with water to reduce the length of the polymer and liberate a glucose molecule

33
Q

How is fructan hydrolysed?

A

Fructanase will combine the fructan with water to reduce the length of the polymer and liberate a fructose molecule

34
Q

What is the purpose of enolase?

A

A key regulatory enzyme in glycolysis

35
Q

What ion inhibits action of enolase?

A

Fluoride

36
Q

What is the effect of fluoride inhibition on enolase?

A

Reduced sugar transport because PEP is a key component of PTS system
Reduced acid production because pyruvate production is reduced

37
Q

What is the most commonly used prebiotic?

A

xylitol

38
Q

What does xylitol do?

A

Inhibits growth of s.mutan in vitro

Inhibits glycosyl transferase in cariogenic bacteria

PMI (16 decks)

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