PMI02-2016 Flashcards
What are the two species of mutans streptococci found in humans?
S. mutans
S. sobrinus
What are the four factors required for caries development?
Teeth
Bacteria (plaque)
Time
Fermentable carbohydrates
What evidence is there that implicated Streptococcus mutans in caries?
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
What virulence factors does S. mutans have and what do they do?
Antigen I/II = adherence
Glucosyl transferase = produce glucan polymers from sucrose
Glucan binding protein = attach cells to glucan
Describe the association between Lactobacilli and caries.
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
What type of organism are Veillonella species?
Gram-negative anaerobic cocci
Describe the association between Veillonella and caries.
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
What is the general consensus about caries microbiology from recent culture and DNA-based studies?
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
What do Veillonella species use as a growth substrate?
Lactate
What acidogenic species are significantly associated with carious lesions?
Scardonia wiggsiae
Propionibacterium acidifaciens
Bifidobacteria
Lactobacilli
How did Bradshaw et al., 1989 demonstrate the role of pH on caries ecology?
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
What pH is generated by the action of S. mutans and other Streptococci on sugars?
4-5
What species often dominate cavitated lesions in dentine?
S. mutans
Lactobacilli
Outline the extended ecological plaque hypothesis.
- Dynamic stability stage (health) = mild/infrequent acidification; net mineral gain
- Acidogenic stage = moderate/frequent acidification
- Aciduric stage = severe/prolonged acidification, lots of fermentable carbohydrates consumed; net mineral loss
Describe the dynamic stability stage of the extended ecological plaque hypothesis.
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
Describe the acidogenic stage of the extended ecological plaque hypothesis.
Initiated by:
- repeated, raised levels of sugar intake
- reduced salivary flow
- poor OH
Microbiota typically dominated by Actinomyces and non mutans streptococci species
Describe the aciduric stage of the extended ecological plaque hypothesis.
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
What are species commonly found in root carious lesions?
S. mutans
Lactobacilli
Actinomyces
Bifidobacteria
What does α-amylase do?
Converts starch –> glucose + maltose
Binds with high affinity to oral streptococci and retains activity when bound
Involved in bacterial adherence to the pellicle
Give some examples of sugars that can be fermented by plaque.
Sucrose
Maltose
Malto-oligosaccharides
N-acetyl neuraminic acid/sialic acid
What is the main method of sugar transport into bacterial cells?
Phosphotransferase system (PTS)
What is the end product of glycolysis?
Pyruvate
What is the final reaction of glycolysis? What are the products used for?
PEP –> pyruvate + ATP
ATP for PTS (sugar transport)
Pyruvate = key metabolic intermediate
How does the phosphotransferase system work?
Glucose binds PTS extracellularly
ATP (from glycolysis) used to phosphorylate it to glucose-6-phosphate so it can be transported in
What are the functions of extracellular polysaccharides?
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
Which of dextran and levan are more easily removed? What species synthesises each of these?
Levan is more easily removed
Dextran = S. mutans
Levan = S. salivarius
How many glucosyl transferases does S. mutans express? What do each of them produce?
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
What are the main functions of water-insoluble glucans in plaque?
Give plaque bulk and form a sticky mass to aid adhesion
What mediates attachment of bacterial cells to glucan?
Glucan binding protein (Gbp)
What reaction does glucosyl transferase catalyse?
Sucrose + glucan(n) primer –> glucan(n+1) + fructose
What reaction does fructosyl transferase catalyse?
Sucrose + fructan(n) primer –> fructan(n+1) + glucose
What is another name for glucosyl transferase?
Dextran sucrase
What is another name for fructosyl transferase?
Levan sucrase
What reaction does glucanase catalyse?
Glucan(n) + water –> glucan(n-1) + glucose
What reaction does fructanase catalyse?
Fructan(n) + water –> fructan(n-1) + fructose
What enzyme catalyses the reaction sucrose + glucan(n) primer –> glucan(n+1) + fructose?
Glucosyl transferase/dextran sucrase
What enzyme catalyses the reaction sucrose + fructan(n) primer –> fructan(n+1) + glucose?
Fructosyl transferase/levan sucrase
What enzyme catalyses the reaction glucan(n) + water –> glucan(n-1) + glucose?
Glucanase/dextranase
What enzyme catalyses the reaction fructan(n) + water –> fructan(n-1) + fructose?
Fructanase/levanase
What key regulatory enzyme of glycolysis is inhibited by fluoride?
Enolase
What reaction does enolase catalyse?
2-phosphoglycerate –> PEP
What does inhibition of enolase by F- result in?
Reduced sugar transport as PEP is required for the ATP-producing reaction for PTS to function
Reduced acid production as pyruvate production is reduced
What is the most commonly used prebiotic?
Xylitol
What effects does xylitol have?
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
