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BDS2 PMI > PMI02-2016 > Flashcards

PMI02-2016 Flashcards

1
Q

What are the two species of mutans streptococci found in humans?

A

S. mutans

S. sobrinus

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2
Q

What are the four factors required for caries development?

A

Teeth

Bacteria (plaque)

Time

Fermentable carbohydrates

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3
Q

What evidence is there that implicated Streptococcus mutans in caries?

A

S. mutans found in high numbers in carious lesions

Significantly higher salivary count of S. mutans in subject with active caries (>10^6/ml) compared to those without active caries (<10^3/ml)

S. mutans is acidogenic and aciduric so can survive in carious lesions

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4
Q

What virulence factors does S. mutans have and what do they do?

A

Antigen I/II = adherence

Glucosyl transferase = produce glucan polymers from sucrose

Glucan binding protein = attach cells to glucan

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5
Q

Describe the association between Lactobacilli and caries.

A

Very low levels of lactobacilli in caries-free individuals

Appear to be opportunist organisms that require a low pH habitat - do not initiate caries but colonise existing lesions

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6
Q

What type of organism are Veillonella species?

A

Gram-negative anaerobic cocci

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7
Q

Describe the association between Veillonella and caries.

A

Veillonella require lactate as growth substrate = may be present in carious lesions due to high lactate levels

Possible could be beneficial in reducing lactate in lesions but little evidence for this

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8
Q

What is the general consensus about caries microbiology from recent culture and DNA-based studies?

A

Carious lesions have a complex bacterial community

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:

  • Scardonia wiggsiae
  • Propionibacterium acidifaciens
  • Bifidobacteria
  • Lactobacilli
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9
Q

What do Veillonella species use as a growth substrate?

A

Lactate

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10
Q

What acidogenic species are significantly associated with carious lesions?

A

Scardonia wiggsiae

Propionibacterium acidifaciens

Bifidobacteria

Lactobacilli

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11
Q

How did Bradshaw et al., 1989 demonstrate the role of pH on caries ecology?

A

Lab model with 9 oral bacteria species growing together in continuous culture

Pulsed with glucose on 10 consecutive days

Led to fall in pH and increase in S. mutans and Lactobacilli

If pH was held at 7 by addition of alkali, there was no change in microbiota composition

Therefore, change in microbiota was a response to change in pH/environment, NOT THE CAUSE

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12
Q

What pH is generated by the action of S. mutans and other Streptococci on sugars?

A

4-5

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13
Q

What species often dominate cavitated lesions in dentine?

A

S. mutans

Lactobacilli

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14
Q

Outline the extended ecological plaque hypothesis.

A
  1. Dynamic stability stage (health) = mild/infrequent acidification; net mineral gain
  2. Acidogenic stage = moderate/frequent acidification
  3. Aciduric stage = severe/prolonged acidification, lots of fermentable carbohydrates consumed; net mineral loss
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15
Q

Describe the dynamic stability stage of the extended ecological plaque hypothesis.

A

Acid produced by sugars by a range of bacteria lowers the pH of plaque

Followed by alkalinisation phase caused by:

  • acid diffusion
  • buffering by plaque and saliva constituents
  • production of alkali/ammonia by bacteria by ureolysis or arginine deiminase
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16
Q

Describe the acidogenic stage of the extended ecological plaque hypothesis.

A

Initiated by:

  • repeated, raised levels of sugar intake
  • reduced salivary flow
  • poor OH

Microbiota typically dominated by Actinomyces and non mutans streptococci species

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17
Q

Describe the aciduric stage of the extended ecological plaque hypothesis.

A

After a prolonged acidogenic stage, buffering capacity is lost and bacteria changes with selection of aciduric species (esp S. mutans and lactobacilli, some Bifidobacterium and Propionibacterium species)

Ecological change drives the change in microbiota

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18
Q

What are species commonly found in root carious lesions?

A

S. mutans

Lactobacilli

Actinomyces

Bifidobacteria

19
Q

What does α-amylase do?

A

Converts starch –> glucose + maltose

Binds with high affinity to oral streptococci and retains activity when bound

Involved in bacterial adherence to the pellicle

20
Q

Give some examples of sugars that can be fermented by plaque.

A

Sucrose

Maltose

Malto-oligosaccharides

N-acetyl neuraminic acid/sialic acid

21
Q

What is the main method of sugar transport into bacterial cells?

A

Phosphotransferase system (PTS)

22
Q

What is the end product of glycolysis?

A

Pyruvate

23
Q

What is the final reaction of glycolysis? What are the products used for?

A

PEP –> pyruvate + ATP

ATP for PTS (sugar transport)

Pyruvate = key metabolic intermediate

24
Q

How does the phosphotransferase system work?

A

Glucose binds PTS extracellularly

ATP (from glycolysis) used to phosphorylate it to glucose-6-phosphate so it can be transported in

25
Q

What are the functions of extracellular polysaccharides?

A

Contribute to adherence of bacteria to pellicle and plaque

Increase resistance of bacteria to being washed away and to antibiotics

Source of sugar for metabolism and growth when host is fasting

26
Q

Which of dextran and levan are more easily removed? What species synthesises each of these?

A

Levan is more easily removed

Dextran = S. mutans

Levan = S. salivarius

27
Q

How many glucosyl transferases does S. mutans express? What do each of them produce?

A

3

GTFB and GTFC = water-insoluble glucans, rich in α-1,3-glycosidic bonds

GTFD = water-soluble glucans, rich in α-1,6-glycosidic bonds

28
Q

What are the main functions of water-insoluble glucans in plaque?

A

Give plaque bulk and form a sticky mass to aid adhesion

29
Q

What mediates attachment of bacterial cells to glucan?

A

Glucan binding protein (Gbp)

30
Q

What reaction does glucosyl transferase catalyse?

A

Sucrose + glucan(n) primer –> glucan(n+1) + fructose

31
Q

What reaction does fructosyl transferase catalyse?

A

Sucrose + fructan(n) primer –> fructan(n+1) + glucose

32
Q

What is another name for glucosyl transferase?

A

Dextran sucrase

33
Q

What is another name for fructosyl transferase?

A

Levan sucrase

34
Q

What reaction does glucanase catalyse?

A

Glucan(n) + water –> glucan(n-1) + glucose

35
Q

What reaction does fructanase catalyse?

A

Fructan(n) + water –> fructan(n-1) + fructose

36
Q

What enzyme catalyses the reaction sucrose + glucan(n) primer –> glucan(n+1) + fructose?

A

Glucosyl transferase/dextran sucrase

37
Q

What enzyme catalyses the reaction sucrose + fructan(n) primer –> fructan(n+1) + glucose?

A

Fructosyl transferase/levan sucrase

38
Q

What enzyme catalyses the reaction glucan(n) + water –> glucan(n-1) + glucose?

A

Glucanase/dextranase

39
Q

What enzyme catalyses the reaction fructan(n) + water –> fructan(n-1) + fructose?

A

Fructanase/levanase

40
Q

What key regulatory enzyme of glycolysis is inhibited by fluoride?

A

Enolase

41
Q

What reaction does enolase catalyse?

A

2-phosphoglycerate –> PEP

42
Q

What does inhibition of enolase by F- result in?

A

Reduced sugar transport as PEP is required for the ATP-producing reaction for PTS to function

Reduced acid production as pyruvate production is reduced

43
Q

What is the most commonly used prebiotic?

A

Xylitol

44
Q

What effects does xylitol have?

A

Replaces sucrose so decreases caries index - lack of sucrose and few oral bacteria can produce acid using xylitol

Inhibits growth of S. mutans in vitro

Reduces sucrose consumption passively

Transported into S. mutans by fructose-PTS but enters a futile cycle that uses up energy

Inhibits glucosyl transferase in cariogenic bacteria

BDS2 PMI (21 decks)

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