Dental biofilm (plaque) formation

Question 1

Approximately how many microbial species are present in the oral microbiome?

Answer 1

700-800

Question 2

What are the 2 types of bacteria found in the mouth?

Answer 2

Planktonic

sessile

Question 3

What does it mean if a bacteria is planktonic?

Answer 3

The microorganisms that are not attached but are free-floating in an aqueous environment are termed planktonic cells (e.g. in saliva)

Question 4

What does it mean if a bacteria is sessile?

Answer 4

It means that it is fixed or adhered to something (e.g. like the biofilm to tooth surface)

Question 5

What are the 3 types of bacteria found in the mouth??

Answer 5

Indigenous

Supplemental

Transient

Question 6

What is the definition of plaque?

Answer 6

Complex microbial community that develops on the tooth surface (and other hard, non-shedding materials), embedded in a matrix of polymers of bacterial and salivary origin

Question 7

NAME the 4 stages involved in plaque/biofilm formation

Answer 7

1. Acquired pellicle formation
2. Pioneer microbial colonizers
3. Coaggregation
4. Maturation

Question 8

What is a pellicle?

Answer 8

Pellicle is a protein-based layer that covers all orally exposed surfaces of the teeth.

Question 9

What are the proteins found in saliva?

Answer 9

Glycoproteins

Phosphoproteins

Question 10

Bacteria can’t directly attach to a clean enamel surface. Why are the glycoproteins and phosphoproteins in saliva able to directly attach to enamel?

Answer 10

Because enamel is negatively-charged due to its negative phosphate group. The glycoproteins and phosphoproteins found in saliva are positively charged so are able to attract and attach.

Question 11

What 4 species of bacteria are able to attach to the pellicle and start the formation of a biofilm?

Answer 11

Streptococci
Actinomyces
Haemophilus
Neisseria

Question 12

Why do oral bacteria produce extracellular polysaccharides?

Answer 12

They produce them for carbohydrate storage as they are subjected to ‘feast and famine’ cycles (as people aren’t constantly eating)

Question 13

name the 2 enzymes that are produced by the oral bacteria forming a biofilm

Answer 13

Glucosyltransferase

Fructosyltransferase

Question 14

What is produced by the reaction with the enzyme glucosyltransferase?

Answer 14

Glucan (polymer of glucose molecules) + fructose

Question 15

What is produced by the reaction with the enzyme fructosyltransferase?

Answer 15

Fructan (polymer of fructose molecules) + glucose

Question 16

What is microbial succession and why is it important in biofilm formation?

Answer 16

Microbial succession is when the microorganisms present alter the environment making it more habitable to other microbial species so that they are also able to grow.

This can be achieved by the products of the bacteria’s metabolism being a source of energy for another species, or by the by-products altering the pH, for example.

It is important as it allows the biofilm to grow and become more diverse.

Question 17

What is the definition of syntrophism?

Answer 17

It is a mutual dependence of different types of organisms for the satisfaction of their respective nutritional needs. The intermediate or end products of metabolism of one organism are essential materials for another.

Question 18

What is coaggregation?

Answer 18

Coaggregation is a process by which genetically distinct bacteria become attached to one another via specific molecules.

Question 19

What is the result of coaggregation on the biofilm?

How long does this take to occur?

Answer 19

It makes it more diverse

7-10 days

Question 20

What is an example of a bridging species in the coaggregation step of biofilm formation?

Answer 20

Fusobacterium Nucleatum.

Question 21

How does Fusobacterium Nucleatum function in further establishing the biofilm?

Answer 21

It has adhesins which allows other species to attach to the biofilm and cause it to become more established.

Question 22

During the maturation phase of the biofilm, does the growth rate speed up or slow down?

Answer 22

Slows down

Question 23

During the maturation phase of the biofilm, extracellular polysaccharides are continuously produced. What is the reason for this?

Answer 23

It gives the biofilm structural integrity and tolerance to environmental factors and antimicrobials.

Question 24

What is materia alba?

Answer 24

It is soft accumulations of bacteria, tissue cells, and food particles that lack organised structure of the dental biofilm. it is loosely attached and easily displaced.

Question 25

In subgingival plaque- from where do the bacteria obtain their required nutrients?

Answer 25

They obtain nutrients from the periodontal tissues, gingival crevicular fluid, blood supply or other microorganisms