CAP 6 - Caries, Development and biofilms

Question 1

Describe the features of planktonic growth.

Answer 1

• Single bacteria suspended in a media (rich or nutrient limiting)
• Theoretically identical conditions (shaking, aeration or mixing leads to batch cultures
• Low to high density growth, usually exponential (classic growth phase, lag exponential, stationary and decline)
• Limited contact/co-aggregation (cells should separate individually , starvation/high density can secrete material or alter growth to form rafts and develop into biofilm)

Question 2

What are the stages of planktonic growth?

Answer 2

• Planktonic bacteria approach surface
• contact and attachment
• adherence and changes in cell surface
• metabolic activity changes environment
• Quorum sensing and development
• Mature biofilm can seed new planktonic cells into the environment

Question 3

What is the sensory input of prokaryotic development?

Answer 3

• Starvation

- High population density

Question 4

What is the response/development pathway to the sensory input of prokaryotic development?

Answer 4

• Biofilm formaJon (can be combined)
• Competence
• Motility & Chemotaxis
• Endospore formaJon
• Scavenging enzymes
• Release of antibiotics
• Persistor cell state

Question 5

what is the transition from planktonic growth to a biofilm?

Answer 5

developmental pathway

Question 6

Describe the stages of sporulation that lead to the production of a dormant spore which is insensitive to antibiotics (bacillus subtilis).

Answer 6

• axial filament formation
• asymmetric septation
• spore formation
• release
• dormant spore (which then goes under germination and can enter the vegetative cycle)

Question 7

what is involved in the control of gene expression?

Answer 7

sigma factor

Question 8

What is the phosphorelay of B. subtilis?

Answer 8

A system for integrating environment signals into entering development pathway

Question 9

Describe what happens during phosphorelay of B. subtilis.

Answer 9

passing on phosphate groups until a spore is produced?

Question 10

what results in spore formation?

Answer 10

networks of coordinated sigma factors

Question 11

What is a biofilm?

Answer 11

name given to microbial communities attached to a surface

Question 12

What are the properties of a typical biofilm?

Answer 12

– Cooperation/coordination of behaviour (gene expression)
– Structure; microcolonies with channels
– Microenvironments; from pH to 02 tension
– Protection; matrix can protect, different cell state can protect

Question 13

what does plaque extend?

Answer 13

habitat range (increases ability to survive)

Question 14

what are the development stages of plaque :an oral biofilm?

Answer 14

– Pellicle formation
– Attachment of individual bacterial cells (0- 24hrs)
– Growth of individual bacteria (microcolonies formed) (4-24hrs )
– Microbial succession & diversification (1-7 days)
– Climax community (>7 days)

Question 15

what are key features of plaque :an oral biofilm?

Answer 15

– Cells have switched away from planktonic growth (Signaling molecules)
– Matrix (Extracellular polymeric substances)
– Nutrient gradients
– Void spaces (Distribute nutrients/remove waste products)
– Differentiation & Development
– Inter species associations (Food chains, competition etc)

Question 16

What is the definition of Quorum sensing?

Answer 16

The process in which single-celled organisms monitor their population density by detecting the concentration of small, diffusible signal molecules produced by the cells themselves
(sensing availability of ions , substrates , feedback is then given -ve /+ve)

Question 17

What is specific plaque hypothesis?

Answer 17

caries down to a limited number of bacteria

Question 18

What is non-specific plaque hypothesis?

Answer 18

caries outcome of overall activity of microbes

Question 19

What is the ecological plaque hypothesis?

Answer 19

– No specific mix of microorganisms at a lesion
– Environmental change shifs proportion of
subset of bacteria
– Caries; high/frequent sugar intake favours acidogenic/acidoduric bacteria

Question 20

what do surface that are constantly covered by biofilm not develop? (ecological plaque hypothesis)

Answer 20

caries

Question 21

what is occasionally but regularly not found in caries sites? (ecological plaque hypothesis)

Answer 21

mutans streptococci

Question 22

what has an impact in ecological plaque hypothesis?

Answer 22

diet and enamel chemistry

Question 23

what varies in ecological plaque hypothesis?

Answer 23

• structure of biofilm and location of mutans streptococci
• number and location of lactate-consuming species varies
• species generating alkali conditions

Question 24

Name prevention strategies.

Answer 24

•  Oral hygiene
–  (toothbrushing etc.) 
•  Diet
– Carbohydrate/sucrose, acid erosion 
•  Fissure Sealing
– Hall technique, excluding nutrients/carbohydrate 
•  Fluoride
•  Nutrient control
•  Control of biofilm pH
–  Sugar substitutes (e.g. Xylitol)
–  Antimicrobial agents (e.g. chlorohexidine)
–  Fluoride
•  Novel strategies;
–  Prevent colonisation by species (e.g. vaccines) or replace with less virulent strains

Question 25

Give summary slide.

Answer 25

• Planktonic Growth
• Biofilm
• Developmental switches, Quorum sensing
• Ecological Plaque hypothesis
• Prevention strategies take into account understanding of the plaque caries link
• Field continues to develop through research