OE L30 Integument Formation

Question 1

What is the EPS matrix?

Answer 1

The extracellular polysaccharide matrix.

Provides foundations for the bacterial colony to build upon and thrive.

Question 2

Which early coloniser allows EPS formation?

Answer 2

S.mutans.

• They secrete glucosyltransferases
• Glucosyltransferases convert sucrose to glucan (a polymer)

Question 3

How does glucan lead to EPS formation?

Answer 3

• Glucans have alpha 1,3 linkages (crosslinks) which are insoluble
• These crosslinks are responsible for matrix formation and forming a stable biofilm
• Provides attachment sites for bacteria and stabilises the plaque structure, prevents abrasion of plaque through salivary flow

Glucan is an important virulence factor for caries

Question 4

What are the 3 main types of glucosyltransferases secreted by S.mutans?

Answer 4

• GtfB: produces insoluble 1,3 linked glucan
• GtfC: produces a mixture of insoluble 1,3 and soluble 1,6 glucan
• GtfD: produces 1,6 soluble glucans only (useless)

Question 5

Which glucan type is involved in matrix formation?

Answer 5

Insoluble 1,3 linked glucan.

1,6 linked glucans are soluble and do not help EPS matrix formation.

Question 6

Describe the action of GtfC.

Answer 6

• Has binding motifs to lysozyme and amylase in the pellicle
• Attaches to the pellicle
• If sucrose is present, the enzyme can begin conversion to glucan to produce the EPS matrix

Question 7

Describe the action of GtfB.

Answer 7

• Has binding motifs to bacteria
• Transfers glucosyltransferase activity from S.mutans to other bacteria e.g. L.casei which then synthesise the EPS matrix

Question 8

How is pH lowered due to the presence of the EPS matrix?

Answer 8

• The EPS matrix is composed of sugars so can be metabolised
• Lactic, acetic, propinoic and formic acid produced
• Lowers pH, this upregulates GTF synthesis by S.mutans and increases matrix production
• This enables other aciduric organsims to colonise the biofilm, increased biofilm diversity, increased caries risk
• P.gingivalis also binds in these acidic conditions

Question 9

Why is it more challenging to return above critical pH in complex biofilms?

Answer 9

• Saliva cannot diffuse as efficiently through biofilm

- There are acidic niches which have higher acid concentration and can cause localised enamel loss

Question 10

What are Ftfs?

Answer 10

Fructosyltransferases:

• A type of sugar transferase found in various bacteria
• Not a virulence factor
• Comvert sucrose to fructan which is readily broken down and therefore not involved in plaque formation

Question 11

The EPS acts as a virulence factor for caries, how can we reduce EPS formation?

Answer 11

• Dietary changes
• Chlorhexidine mouthwash inhibits GtfC
• Cranberries contain pro-anthocyanidin which blocks Gtfs from binding to pellicle

Question 12

What oral diseases are associated with biofilms?

Answer 12

Caries
- Functional consequence of plaque acids

Gingivitis

• Colonisation of certain bacteria e.g. P.gingivalis
• Bacterial biofilm activates host immune system causing inflammation

Periodontitis

• Host immune response to biofilm, production of inflammatory cytokines
• Cytokines induce synthesis of collagenases: causing tissue and bone loss

Calculus and Supragingival Calculus

• Example of bacterial colonisation
• A calcium reinforced biofilm
• Supragingival calculus is associated with nearby salivary ducts, protein formation promotes adhesion of bacteria to tooth

Question 13

Describe anti-tartar agents.

Answer 13

• Present in oral hygiene products
• Act as inhibitors of mineralisation or slow down crystal growth
  E.g. zinc salts, polyphosphates, pyrophosphates

Question 14

What are the underlying mechanisms of calculus formation?

Answer 14

• Precipitation and nucleation
• pH rises and ions precipitate
• Various nucleation molecules e.g. acidic proteins, GAGs