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