integument formation - biofilms Flashcards
What is required for the stabilisation of plaque?
synthesis of a bacterial extracellular polysaccharide “matrix” (EPS)
explain these results
no bacterial aggregation on gucose
bacterial aggregation shown on sucrose
- bacteria aggregate when coming into contact with dextran (glucan)
- the bacteria begin to lay down the extracellular polysaccharide matrix
What converts sucrose to glucan?
enzymes : glucosyltransferases (Gtf’s)
what makes glucans soluble
contain a higher proportion of alpha 1-6 linked glucans
what makes glucans insoluble?
contain predominantly alpha 1-3 linked glucans
which glucans are involved in establishing an EPS matrix
insoluble glucans
therefore they are virulence factors
give examples of S.mutants glucotransferases and what glucans they form
- GtfB:
- insoluble glucan α1,3 linked glucan
- Very important for stabilisation of the EPS matrix
- GtfC:
- mixture of soluble α1,6 linked glucan & insoluble
- GtfD: soluble glucans
- Not involved in establishing EPS matrix
- Not a virulence factor
what is the significance of the C-terminal repeat motifs in GtfC
- able to bind to lysosyme and amylase in the saliva
- allowing Gtf to bind to the pellicle
- enzymes can be sequestered to the tooth surfaces through the pellicle
- drives production of the EPS matrix
What changes to the properties of Gtf occurs when binding to the pellicle?
Gtf becomes hyperactive
- more capable to form crosslinkings that lead to the stabilisation of the EPS matrix
- more stable at a wider pH range
- can more optimally convert sucrose into glucans
- therefore increase in insoluble glucan synthesis
- most establishment of EPS matrix
what does a signal peptide on Gtf’s show?
which Gtf’s contain them
the enzyme is secreted by the bacteria into the oral environment
both GtfC and GtfB have a signal peptide
What is the significance of the C-terminal repeat motifs in GtfB?
- It can form bacterial binding sites
- allows transfer of Gtf activity from S.mutants to other bacterial species
- increased synthesis of EPS matrix
how does the EPS matrix lead to a drop in oral pH??
What effect does this drop in oral pH have on Gtf and the EPS matrix?
- EPS matrix is able to be metabolised to acid like sugars
- therefore drop in pH
- leads to
- upregulation of some Gtf activity
- upregulation of synthesis of Gtf’s by s.mutants
- increase in matrix production
What other bacteria can further colonise the EPS and how do they effect health?
- acidogenic or aciduric bacteria can colonise the biofilm
- further establishment of diversity
- increased caries risk
- P.gingivalis
- increased gingivitis risk
what are EPS-microcolonies?
- acidic niches in the biofilm
- areas that retain acid for prolonged periods of time
- high bacterial colonisation
- where enamel erosion will occur
What evidence of is there to show the importance of Gtf’s as virulence factors
Genetically modified S.mutants lacking genes encoding glucosyl transferases – GtfB/C
- did not form EPS-microcolony complexes
- can be readily neutralised
- matrix was not crosslinked
- less complex structures
- fail to generate acid environments
- can be readily neutralised
What do fructosyltransferases
role?
convert sucrose into fructan and glucose
fructan is soluble and readily broken down
not involved in plaque formation
what counter measures are there for EPS formation?
- change diet
- chlorhexidine mouthwash inhibits GtfC
- Cranberry pro-anthocyanidin oligomers block Gtf bound to saliva coated HA
- Able to block Gtf’s in the pellicle
Why is it difficult to stop EPS formation?
- inhibition of Gtf activity in biofilms is less effective
- Much more difficult to fight bacteria which are in the biofilm
What is the normal flora of the oral cavity and teeth surfaces
- Microbes will always colonise tooth surfaces
- Most are not dangerous to us
- Some cause disease
- Commensal microflora ( indigenous / resident ) and transient microflora exist in perfect harmony with the host
- When relationship is broken
- Environmental disaster
What are the oral diseases associated with biofilms?
- caries formation
- periodontal disease
- tartar formation
summary of stages of periodontitis
begins with gingivitis
- Inflammation of gingiva only
- Caused by bacterial biofilm
- Activates host immune system
periodontitis
- Severe inflammation of periodontal ligament
- Caused by host immune system
- Activation & secretion of proinflammatory cytokines
- Leads to induction of synthesis of proteinases that can break down bone in extracellular environment
- Cytokines induce enzyme synthesis
- Collagenase = bone loss
- Neck of tooth becomes exposed due to gum line recession
- Leads to tooth loss
where does supra-gingival calculus usually form?
- Especially associated near salivary ducts
- Where protein concentration important for pellicle formation is high
- Saliva main source of Ca2+ & PO42-
what is calculus
calcium reinforced biofilm
when Ca precipitates on enamel surfaces
highly undersirable
huge removal force required to detach
what factors are involved in calculus formation
- oral fluids (saliva / GCF)
- bacteria
- seeding / nucleating molecules
- diet
what is the mechanisms of calculus formation
Pathological calcification so no specific mechanism
- precipitation and nucleation
- pH rises & ions precipitate
- various nucleation molecules (acidic proteins, GAGs)
