Microbiology of caries Flashcards
What are biofilms made up of?
Diverse composition of 700+ species with bacteria, fungi and viruses etc, the composition is relatively stable.
What type of surfaces permit heavy biofilm formation?
Non shedding (teeth, dentures and implants)
What does desquamation help do?
Reduces microbial load on mucosal surfaces
What are the cons of traditional culture?
Laborious, expensive and only 50-70% of microbiota can be cultured. Then multiple tests have to be done to work out what each organism is.
What is the con of light and electron microscopy?
Only cell morphology
What is fluorescent in situ hybridisation?
A probe can be labelled with a fluorescent dye and will bind (hybridise), on the basis of complementary base pairing to the matching DNA in the cells (in situ).
What are the molecular approaches (culture dependent)?
- PCR
- DNA-DNA hybridisation (checkerboard)
- Human microbiome identification microarray - gold standard
- Whole genome sequencing (metagenomics)
What are the databases for oral microbiomes?
Human microbiome consortium
Human oral microbiome database
In health, how is a dental biofilm organised?
Structurally and functionally with anaerobes at the bottom and aerobes at the top/outside with organisms that feed off lactic acid under the tooth surface.
What are features of a multispecies biofilm?
Concerted and collaborative metabolism Food chains Environment modification Matrix formation Cell-cell signalling Complex interactions = balance
What is colonisation resistance?
Colonisation resistance is the term used to describe the microbiota’s capacity to limit the introduction of exogenous microorganisms and pathobiont expansion.
What is cross talk immunomodulation?
Down regulation of potentially damaging pro inflammatory host responses
Stimulation of beneficial host responses
Promoting host-microbe balance (symbiosis)
What is the entero-salivary nitrate circulatory system?
Where dietary nitrate goes from nitrite to acidified nitric oxide which decreases blood pressure and increases gastric mucus which has an antibacterial effect.
What organisms are involved in dental health?
Strep mitis/oralis Actinomyces spp Haemophilus spp Nieseria spp Fusobacterium spp
What organisms are involved in caries?
Acid tolerating bacteria:
Mutans streptococci
Lactobacilli
Bifidobacterium
What are the drivers of change (what causes caries)?
Key oral micro-organisms, susceptible host (uncleaned tooth surface) and environmental factors (frequent fermentable carbohydrates, poor oral hygiene, low salivary flow rate)
What are confounding factors in the development of caries?
Fluoride availability, diverse natural microbiota and non specific virulence traits.
What are gnotobiotic animal studies?
Animals not exposed to micro-organisms the micro-organism is introduced to see the effect without confounding factors.
What are cross sectional human epidemiology studies?
A cross-sectional study involves looking at data from a population at one specific point in time. They only show association not causation (bacteria could increase as a consequence of caries) however they are cheap.
What are longitudinal studies?
Subjects are followed over time with continuous or repeated monitoring of risk factors or health outcomes, or both. They do show cause and effect but are expensive.
What are mutans streptococci?
Gram positive cocci/rods/cocco-bacilli
Found on non shedding surfaces
Implicated in initiation of caries
What are lactobacilli?
Gram positive rod found in advanced dental caries
What are bifidobacteria?
Gram positive rod with branched cells implicated recently in caries
What are the challenges in sampling bacteria for caries studies?
Disease occurs at sites with natural diverse microbiota and pathogens found at healthy sites as minor components of biofilm.
Difficult then to correlate microbiota to enamel status
Lesions can remineralise and compromise studies
Multifactorial causes of caries
What is the relationship found in cross sectional culture studies in regards to strep mutans?
Increased MS at caries sites
Inverse relationship - MS and sanguinis
Some sites with caries have no MS
Not diagnostic as some caries free fissures has MS
Can caries occur in absence of MS?
Yes
What are acidogenic microorganisms?
Strep mitis, strep oralis, actinomyces, bifidobacterium
What micro-organism produces acid the fastest?
Strep sobrinus
What are base generating species?
S-salivarius (urea)
S-sanguinis (arginine)
A.naeslundii (urea)
What do strep dentisani and strep a12 do?
Create ammonia which is arginolytic and inhibits streotococcus mutans.
What does urea get broken down into?
By urease into ammonia and CO2
How does arginine make ammonia?
Arginine - citrulline + ammonia
What do culture independent approaches confirm the role of?
Bifidobacterium, scardovia, parascardovia, candida spp tending to have similar properties (acid producing and acid tolerating)
What organisms are involved in nursing bottle caries?
MS and lactobacilli
What organisms are involved in root surface caries?
Actinomyces spp thought to be at first but recently actinomyces israelii, a gerenseriae and s mutans, gram negative rods.
What organisms are involved in early childhood caries?
Scardovia wiggisae, slackia exigua and granulocatella eligans
What organisms are on non carious healthy tooth tissues?
Strep cristatus, s gordonii, s sangunis, corynebacterium matruchotii, neisseria flavencens.
What is the culture found in infected dentine?
S mutans, lactobacilli, actinomyces spp, gram negative rods.
What are characteristics of cariogenic bacteria?
Rapid sugar transport and acid production
Acidurity
Extracellular polysaccharide
Intracellular polysaccharide - stored sugars
How does caries form?
Fermentable sugars - plaque - rapid acid production - demineralisation
Do pathogens produce virulence factors in caries/gingivitis?
No
Do pathogens in caries/gingivitis satisfy Koch’s postulates?
No as not all bacteria are present in every case of the disease.
Where do cariogenic organisms come from?
Transmission - mother to baby
How does dysbiosis occur?
Major ecological pressure that alters competitiveness for organisms - frequent sugar, acidic pH - more cariogenic organisms.
Beneficial bacteria are more competitive in healthy oral conditions.
What is the specific plaque hypothesis?
Specific pathogens have specific roles - cause caries
What is the non-specific plaque hypothesis?
Many species have roles, outcome is caused by all the organisms activities.
What is the ecological plaque hypothesis?
Disease is preventable and controllable by direct inhibition of causative organisms and promotion of a natural balance (symbiosis) interfering with factors driving dysbiosis.
What does the ecological plaque hypothesis suggest?
Specificity in disease due to microbial function not name
Many species can contribute
Environmental regulation of gene expression
How do we control caries disease?
Direct inhibition of causative organisms
Maintenance of natural balance (homeostasis)
Interference with factors driving shifts in microbiota that delete healthy bacteria.
What factors cause caries?
Low pH, low salivary flow, bad OH, low fluoride levels, cariogenic diet.
Why is sucrose a driver of dysbiosis?
Sticky slime (extracellular) breaks down intracellular polymers (food reserves) in absence of sugar ferments into lactic acid lowering pH.
What are approaches to controlling caries?
Plaque control Fluoride Sugar substitutes Antimicrobial and antiplaque agents Modify microbiota (probiotics/prebiotics) Vaccination Passive immunisation
How does fluoride reduce caries
Inhibits IPS synthesis Reduces glycolysis (inhibits enolase-sugar transport) and acid production Removes competitive opportunity for MS and other acidogenic/aciduric bacteria by eliminating low pH Acidifies cell interior (HF)
What are sugar substitutes?
Sorbitol, Xylitol
Sweeteners examples
saccharin, aspartame
How do sugar substitutes reduce caries?
Not or weakly metabolised to acid and stimulate salivary flow and have weak antimicrobial activity (Xylitol and S mutans)
Why do we use minimum inhibitory concentration drugs?
So beneficial bacteria stay
How does chlorhexidine reduce caries?
Antiplaque and anti mutans streptococci (bactericidal and bacteriostatic depending on dose)
How do antimicrobial and antiplaque agents work?
Add agents to generate alkali (arginine - makes ammonia which is arginolytic inhibits MS) MIC effects (inhibit glycolysis, sugar transport)
How do antimicrobial agents work in periodontitis?
Less protease, less cytotoxin, less capsule and less bacterial growth.
What is replacement therapy?
GM strep mutans, deleted lactate dehydrogenase - no lactic acid, elevated mutacin 1140 production - no strep mutans.
What are prebiotics?
Molecules that stimulate growth of beneficial bacteria (arginine example)
What are active vaccines based on in the mouth?
Whole cells, glucosyntransferases and cell wall associated protein (Ag I/II) but protection only in rodents, not tested on humans.
What is passive immunisation?
Coat surfaces with antibodies or synthetic antibody fragments.
Reduce MS colonisation in primates and humans safe and acceptable.
