Dental Plaque Flashcards
Define plaque
The community of microorganisms found on the tooth surface as biofilm embedded in a matrix of polymer of saliva and of bacterial origin
Describe plaque
Plaque is natural and it contribute to the host defences
It has properties beneficial to the host
Helps regulate the cardiovascular system
Dampens down immune response
What does the term biofilm mean?
Biofilm is a term to describe organism when they are attacked to a surface
In plaque the bacterial are combined with extra cellular proteins from the saliva and some that the bacteria may synthesis themselves
They are ubiquitous
Where is dental plaque often found?
In stagnent areas that are difficult to clean
These are the areas we get the most dental disease
Give an example of a biological biofilm
Dental plaque
What is the main characteristic of biofilms in a clinical situation?
Microorganisms growing on the surface as a biofilm are much less susceptible to antimicrobial agents (like antibiotics) than a suspension of the same micro organism free in liquid
How do biofilms form?
In a sequential order:
- Formation of conditioning film (this is a film of molecules that is absorbed from the envirmnemt that change the properties of the surface
- Transport of microbes
- Reversible phase
- Irreversible phase
- Secondary colonisation (co adhesion)
- Growth and matrix synthesis
- Detachment
How does dental biofilm (plaque form)
- Conditioning film forms on the tooth as the ACQUIRED PELLICLE
- Microbes are then transported to the surface by saliva
- Microbes may then be held there reversibly by electro chemical forces
- If the microbes are held there weekly then a more permeant irreversible phase begins. The organism then binds to the surface by intermolecular interactions between molecules on the bacterial surface (adhesin) to a complimentary receptor in the conditioning film (primary colonisation)
- This then leads to the attachment of a secondary coloniser to the primary coloniser. This is called adhesion over time this attachment leads to and increase in diversion and primary and secondary colonisers are in close proximity so share metabolic interactions and can change the environment making it more favourable for more organism
- Organisms then grow undergoing biofilm maturation and synthesises extra cellular polysaccharides
- Bacteria can sense there environment and if they think the environment isn’t favourable they will detach using the enzymic cleavage of adhesion
What happen to the teeth as soon as they erupt?
They are covered by a thin film of proteins derived from saliva
Bacteria then attaches to this film instead of the tooth itself
Describe the first stage of biofilm formation
Conditioning film begins to form
Conditioning film forms rapidally
Can be a micron in thickness
Most of the molecules derived from the saliva, gingival crevicular fluid and microbes
What is the conditioning film?
Conditioning film is a film of molecules that is absorbed from the envirmnemt that change the properties of the surface
Name some of the molecules that come from the host to make up the acquired pellicle during dental biofilm formation
Amylase (still functional despite being bound to a surface) Immunoglobulins Proline rich peptides (PRP) Mucins Statherin Agglutinins
Name some of the molecules that come from the bacteria to make up the acquired pellicle during dental biofilm formation
Glucosyltransferases
Glycans
Describe the second phase of dental biofilm formation
Transport of microbes
The bacterial are passively moved to the surface by the Flow of saliva
Describe the third phase of dental biofilm formation
Reversible phase
Bacteria will have small electrical charge and the surface will also have a small electrical charge on it
This results in the formation of electrostatic forces between to the 2 charges
This force is weak but can hold the bacteria near the surface allowing the interactions to become more specific
Describe the fourth phase of dental biofilm formation
Irreversible phase
colonisation
Interactions now become specific and over a shorter range
Interactions between molecules on microbial cells (adhesion) and receptors on the surface
This is A very specific interactions
Describe the fifth phase of dental biofilm formation
Secondary colonisation
Attachment of the secondary molecules to the primary coloniser
The secondary molecules don’t have. complimentary receptor to the bacteria in the biofilm but do have a complimentary receptor to the primary coloniser
This allows for the build quo of a more diverse community
What is the function of agglutinins
There function is to bind to microorganism while the are still in saliva, preventing the organism from attaching to the surface as we swallow them
What are cryptitopes?
They are hidden receptors for bacterial adhesion
What are adhesins?
Molecules on the surface of microbial cells that bind to complementary receptors
Which adhesin is found on the strepocuccus spp. bacteria and what is its corresponding receptor?
Adhesin: Antigen I/II
Receptor: Salivary agglutinin
Which adhesin is found on the mutans streptococci bacteria and what is its corresponding receptor?
Adhesin: Glucan binding protein
Receptor: Glucan
Which adhesin is found on the Actinomyces naeslundii bacteria and what is its corresponding receptor?
Adhesin: Type 1 fimbriae
Receptor: Proline rich proteins
Give an example of a molecule that has cryptotopes
Proline rich peptide
These peptides are circular and folded when in saliva and so the receptors for bacteria are hidden (cryptitopes)
When these molecules bind to a surface they unfold exposing the cryptitopes allowing bacteria to bind to the surface
Which bacterium do you see in the first few hour of biofilm formation?
Streptococci sanguinis
Streptococci oralis
Streptococci gordonii
Which organism plays a key role in the co adhesion stage of dental biofilm formation?
Gram negative Fusobacterium nucleatum
This organism will readily bind to any organism in the mouth especially early colonisers
Once attached to the early colonisers Fusobacteria will then allow for later colonisers to bind to it forming a complex and diverse environment of bacteria and micro organism
What are some characteristics of later colonisers
They are more demanding in their requirements
Usually they are strict anaerobes
What is the Fusobacterium nucleatum described as?
A riding molecules between early and late colonisers in oral biofilms
What happens as the biofilm begins to grow and mature?
The organism are in close contact and they start to communicate and interact
They can produce a range of signalling molecules that can diffuse out and tell other similar organism that this biofilm is a favourable place to inhabit
The organisms also begin to interact metabolically forming food chains
The organisms can change the environment eg the pH
They also form gradients and secrete the extraceullar matrix
Name the 5 things organism do as the biofilm begins to mature
- Cell to cell signalling occurs
- They interact metabolically
- They cane the environment slightly
- Form gradients
- Secrete the extracellular matrix
Name some of the cell signalling molecules
- Gram positive bacteria like streptococci produce peptides as signals
- Gram negative bacteria produce a range of molecules other than peptides like Auntoindicer-2
Why are people interested in cell signally molecules
If we could understand what these molecules are saying to different organism we could try and interfere with biofilm production
This can be used to treat cystic fibrosis to try and discourage biofilm formation in the lungs
What is the common food chain commonly studied in dentistry?
The lactate production and utilisation food chain
GLUCOSE is broken down by streptococcus bacteria into LACTATE
LACTATE decreases the pH
LACTATE is then broken down by Veillonella into ACETATE AND PROPIONATE (these are weaker acids so less chance of caries)
What is the most used by bacteria to grow
The glycoproteins which are the mucins that make up most of saliva
Which enzyme breaks down glycoproteins?
Glycosidase
What is the breakdown of glycoprotein chains called?
It is described as the concerted and sequential breakdown of glycoproteins
Bacteria have to work in a systematic way to break down the sugar back bone to expose the protein backbone
What is a consequence of breaking down glycoprotein
They have little effect on pH as they take a lot lower to metabolise
How much of the biofilm is made up of plaque matrix?
Makes up 30% of the plaque volume
What is the plaque matrix made up of?
Polymers derived from the host and bacteria
What does glucosyltransferase (GTF) do?
Breaks down sucroses forming glucans and releases free fructose
What are glucans
A string of glucose molecules
They are often very sticky and insoluble so will stay around in the biofilm
Result in retention of acids as the glucans will not allow saliva to get though and neutralise any acid
What are fructans
A long string of fructoses
What does fructosyltransferase (FTF) do?
Breaks down sucroses forming fructans and releases free glucose molecules
What are the functions of the matrix
- Protection from extreme environments and the hosts defences
- Provide a nutritional reserve (glucans and fructans can be unitises)
- Stabilises the biofilm giving structure support
- Interacts with the molecules retaining enzymes and ions
- Retains water preventing desiccation
- Stops penetration of antimicrobials like antibiotics
What makes up the plaque biofilm?
Bacterial polysaccharides like glucan, mutans, heteropolymers, e-DNA
Bacterial polymers also make up the plaque biofilm
What are nutriphils and where are they produced?
They are the most abundant (40% to 70%) type of white blood cell released by the gingival crevicular fluid
What are the benefits of microbial communities interacting with each other?
Form food chains and was
Work together using all their enzymes to break down nutrients
Cell-cell signalling
Inhibitors are neutralised
Subversion of host defences (eg some bacteria can break down penicillin protecting themselves and the organisms around them)
Gene transfer can occur
What are the disadvantages of microbial communities interacting with each other?
Bacteriocins are produced by some bacteria
Some bacterial can produce hydrogen peroxide limiting anaerobic gram negative bacteria
Some acids produce organic acids lowering the pH
Bacteria must compete for nutrients
What are bacteriocins?
They are molecules produced by bacteria that are inhibitory to neighbouring bacteria causing neighbouring bacteria to die
How can we describe ALL biofilms?
They are all spatially and functionally organise
There is a division of all labour
Theres multiple interactions
Theres interactions between the host environment an the microbial composition and activity
The properties of the community are more than the sum of the activities of the individual species
What might bacteria do if they sense the environment is unfavourable?
They produce an enzyme which breaks there adhesin allowing them to break free from the biofilm and go colonise somewhere else
What are the differences between the early and late stages in biofilm?
Early stages: Limited number of species Mainly streptococci found Mainly a aerobic environment In the late stages: Theres a diverse community 100-300 Species present Many obligately anaerobes Some unculturable anaerobes Cell-cell association Microbial interactions
How might we look at biofilms and see what bacteria they are made up of?
By using the technique:
Fluorescent in situ hybridation (FISH)
Fluorescent dye attached to DNA sequence of bacteria
If bacteria is present in biofilm the probe will attach and fluoresce under a Fluorescent lamp
What are some features of a multi species biofilm?
They are concerted and collaboratively metabolise Form food chains Environmental modification occurs Matrix formation occurs Cell-cell signalling Complex interaction= balance
Describe the composition of fissure biofilm
Mainly streptococci found Saccharolytic Few gram negative Low anaerobes High redox Neutal to acidic pH Influenced by saliva
Describe the composition of gingival crevice biofilm
Gram negative anaerobes present Spirochaetes and unculturable bacteria found Proteolytic Obligately anaerobic neutral to alkaline pH Influened by gingival crevicular fluid
Hoe many species of microorganism may one person harbour?
100-300 species
Name some microbes found at the fissure of the tooth
Gram positive, facultative anaerobes:
Streptococcus
Actinomyces
Name some microbes found at the approximal of the tooth
Gram motive and negative, facultative and obligate anaerobes: Neisseria Streptococcus Actinomyces Prevotella Veillonella
Name some microbes found at the gingival crevice of the tooth
Gram motive and negative, obligate anaerobes: Streptococcus Actinomyces Prevotella Eubacterium Fusobacterium Spirochaetes "unculturables"
What does heterogeneous environment mean and what does it facilitate?
Heterogenous environment means there are gradients present (eg oxygen, metabolic nutrient, carbon dioxide gradient etc)
Helps facilitate microbial diversity
What are some of the properties of plaque biofilm?
- Spatial organisation able to get a structural relationship
- Altered gene expression (both directly and indirectly)
- Increase tolerance to antimicrobial agent :
penetration
inactive and neutralisation
novel phenotype
slow growth rate of bacteria in biofilms
community interactions - Increased resistance to antimicrobial agents
What is the difference between tolerance and resistance?
Tolerance is bacteria having the capacity to endure continued subjection to something such as antimicrobial agents conditions without adverse reaction
Bacteria are able to TOLERATE antimicrobial agents as they are in the plaque biofilm if they weren’t in the biofilm they would die
RESISTANCE is when in or out the biofilm the bacteria would survive either way
What are the two terms used to describe the sensitivity a microbe may have to an antibiotic?
MIC: minimum inhibitory concentration
MBC: minimum bactericidal concentration
What is the MIC
The minimum inhibitory concentration
The lowest conc of that drug which inhibits that pathogen
What is the MBC
The minimum bactericidal concentration
The lowest conc of that drug which kills that pathogen
Why is dental plaque describes as a microbial community
Theres a broader habitat range (ie anaerobes can survive in an aerobic environment)
There is increased metabolic diversity and efficiency (More complex host glycoproteins can be digested)
Theres increased tolerance to antimicrobial agents, inhibitors and host defences
Enhanced pathogenicity
What are so ecological pressures in the mouth
a lot of sugar
diminished saliva flow
What is dysbiosis
Break down of community balance
What are some immunological factors responsible for dysbiosis in the dental biofilms?
sigA deficiency
Neutrophil dysfunction
Chemotherapy induced myelosuppression
Infection induced myelosuppression (eg AIDs)
What are some non-immunological factors responsible for dysbiosis in the dental biofilms?
Xerostomia Antibiotics Medication Dietary carbohydrates resulting in lowered pH Increased GCF flow Oral contraceptives
Conditioning film forms rapidally
Can be a micron in thickness
most of the moelcues
What do Gram positive bacteria produce to signal other cells
Peptides
What do Gram negative bacteria produce to signal other cells?
Range of molecules other than peptides like Auntoindicer-2
Describe the characteristic of early stage biofilm formation
Limited number of species
Mainly streptococci found
Mainly a aerobic environment
Describe the characteristic of later stage biofilm formation
Theres a diverse community 100-300 Species present Many obligately anaerobes Some unculturable anaerobes Cell-cell association Microbial interactions
