Microbiology of caries I Flashcards
Revisit the properties of dental biofilms Review the methods to characterise the oral microbiome Assess the evidence for the role of microbes in caries Describe the main causative bacteria Define the properties of cariogenic bacteria
Give 5 properties of dental biofilms
- Diverse composition (700 +species)
- Bacteria, fungi and viruses
- relatively stable composition over time
- Desquamation reduces microbial load on mucosal surfaces
- ‘Non shedding surfaces’ (denture, teeth,implants)
permit heavy biofilm formation unless its controlled
How do we distinguish between beneficial and pathogenic microorgansmism?
- Traditional culture
-Laborious:expensive: only 50-70% of oral mciorbiota can be cultured
- multiple tests to identify and anime the isolates
- tedious
- different conditions required by different microbiota - Microscopy
- Conventional (light and electron microscopy)
- FISH (fluorescent in situ hybridisation) - Molecular (cult-independent)
- PCR
- DNA-DNA hybridisation
- Human oral microbiome identification microarray (HOMIM) larger number of pre selected species that can be detected
- High thoroughput whole genome sequencing (metagenomics/metatransciptomics)
What 3 characteristics are found in dental biofilms
-Structurally organised
-Functionally organised
-Undergo constant organisation
What are the 6 features of multi-species biofilms
- concerted and collaborative metabolism
- food chains
- environment modification
- matrix formation
- cell - cell signalling
- complex interactions= balance
what does symbiosis mean
oral biofilms are natural and beneficial
what does colonisation resistance involve
-long term antibiotic therapy- overgrowth by yeasts
-excludes exogenous microbes
what is immunomodulation
regulation and modulation of immunity that might be achieved by reducing or enhancing immune response
- down regulation of potentialy damaging pro-inflammatory host reponse
- stimulation of beneficial host response
- promote host-microbe balance
- dietary nitrate - acidified nitric oxide (help decrease bp)
-Blood pressure decreases; gastric mucus increases; antibacterial increases
what are the environmental factors of caries
-cariogenic diete
- frequent femetable sugars
-poor oral hygiene
-low saliva flow rate
what are the confounding factors of caries?
fluoride availabilty
diverse natural mciobiata
non specific virulence traits
what are the 3 types of evidence found for the role of mricobes in aetiology of dental caries
Gnotobiotic
Human epidemiology
Vaccination
How does Gnotobiotic show the role of mricobes in aetiology of dental caries
- controlled environment where usually no microbes present (animal studies)
- specificity- some bacteria are more cariogenic than others
- diet- importance of fermentable sugars
- transmission - from animal to animal
-Antimicrobial agents- effective antimicrobials prevent caries
How does Human epidemiology studies show the evidence for role of microbes in aetiology of dental caries
- cross sectional - cheap but only show associations
- Longitudinal - show cause and effect relationships
How does Vaccination show the evidence for role of microbes in aetiology of dental caries?
rodents and primates- active vaccination can protect
Name 5 implicated microorganisms in caries
Mutans streptococci (MS) (gram+ cocci, found on hard non shedding surfaces, iniation of caries)
Lactobacillus- (gram+ rod advanced dental caries)
Bifidobacteria
Candida
Actinomyces
What are the challenges found in microbial aetiology of dental caries?
- disease occurs at sites with natural, diverse micorbiotia
- pathogens found at healthy sites; often as minor component of multi species biofilms
-difficult to correlate microbiota to enamel status - lesions can remineralise
-Pathogenic traits are relatively non specific - Multifactoral nature of caries
what do some cross sectional human studies show about MS
- MS can increase at caries sites
there is an inverse relationship between MS and S sanguines - Some sites with caries have no MS and vice versa
- 71% of cadres fissures had >10% MS
70% of caries free fissures had no detectable MS
what does longitudinal human studies show of MS
- Confirms increase in MS at caries sites
-Proportions and isolation frequencies
-MS can occur after first signs of deminerlisation - Caries can occur in apparent absence of MS
what is the role of other bacteria and base generating species
S-salivarius- urea
S-sanguinis- arginine
A-naeslundii- urea
urea can produce ammonia which is an alkali
inhibit MS
which bacteria is found in nursing bottle/early childhood caries
MS
Lactobacilli
what is the bacterias found in early studies of root surface caries
Actinomyces spp
what is the bacterias found in later studies of root surface caries
MS
Lactobacilli
what is the bacterias found in recent studies of root surface caries
diverse mcirobtioa
- Actinomyces spp
- MS
-Gram negative rods
What are the characteristics of cariogenic bacteria
- Rapid sugar transport and acid production
- Aciduricity
-Extracellular polysaccharide - Intracellular polysaccharide
what are the characteristics of MS
sugar transport,acid production, tolerance
Rapid sugar transport- multiple systmes
pH 3.9-4.2
Acid tolerance - High - growth at pH 5.5
EPS- soluble
IPS- yes
what are the characteristics of S sanguines
sugar transport,acid production, tolerance
- medium sugar transport
-pH 4.4-4.8 \ - poor acid tolerance
EPS- soluble and insoluble
IPS- yes
Describe the oral microbiome in health and in dental caries
IN HEALTH
- host glycoproteins
- dental plaque
- slow acid production /neutral pH
- little/no demineralisation
IN DENTAL CARIES
- fermentable sugars
- dental plaque
- repaid acid production /low pH
- demineraltion
what is the symbiotic relationship between
host and dental microbiota
- this can breakdown which causes disease (dysbiosis)
which studies prove plaque bacteria causes caries
gnotobiotic animal studios
which bacteria are the most cariogenic species
mutans streptococcus
what does caries require to flourish?
susceptible tooth surface
cariogenic diet
cariogenic microbiota
sufficient time
what are the key pathogenic traits
acid production and acid tolerance
intracellular and extracelllurlar polysachhradie synthesises
