Biofilms and Communication

Question 1

What factors affect the arrival of bacteria onto a surface?

Answer 1

Whether the bacterium is motile and the flow of the medium that they are in (turbulence impaction).
If they are not motile, they have to rely on diffusion to arrive on the surface

Question 2

Describe laminar flow

Answer 2

There are distinct layers within the medium with no mixing

There is a boundary layer (beyond which there is no flow).

Question 3

Examples of organs which are sterile and have laminar flow

Answer 3

Urethra, bladder (going up the kidneys)

Question 4

Describe turbulent flow

Answer 4

There is lots of mixing of the medium and there is a disturbed boundary layer (making it easier for bacteria to attach as the turbulent flow brings bacteria to surface).
Attachment to rough surface is greater than attachment to smooth surface as there is more turbulence.

Question 5

Describe reversible attachment

Answer 5

The bacteria are reversible bound to the surface so that they are 30-100nm from the surface

Because the bacterial cell and eukaryotic cells are both negatively charged they repulse each other

This leads to the bacteria hovering a very short distance above the surface (giving the illusion that they are attached)

Question 6

Describe irreversible attachment

Answer 6

Adhesins are released and used to overcome the repulsion and attach to the surface
In order to attach firmly an exopolymer deposition is released which acts as a glue

Question 7

Give examples of adhesins

Answer 7

Flagella, pilli, fimbriae, stalks and adherence proteins

Question 8

What changes occur to the expression of genes once a bacterium is firmly or irreversibly attached to a surface

Answer 8

There is a down- regulation of planktonic genes such as flagella

There is also an up-regulation of sessile genes such as stress proteins and a capsule or slime

Alg genes produces alginate. Alg genes are up regulated so than an extra cellular polysaccharide is produced

Question 9

Describe the composition of the biofilm matrix

Answer 9

The biofilm matrix is around 98% water and 2-5% cells
Absorbed in the water there are nutrients and oxygen
There is also a large amount of extracellular polysaccharide, nucleic acids, proteins, glycoproteins and phospholipids

Question 10

What are exopolymeric substances (EPS)?

Answer 10

Extracellular polysaccharide, nucleic acids, proteins, glycoproteins, phospholipids

Question 11

How does low flow and low nutrients affect the architecture of a biofilm?

Answer 11

There is slow growth I’d the bacterial number and the biofilm is more compact

Question 12

What is sloughing?

Answer 12

Removal of intact pieces of biofilm of the entire biofilm by fluid frictional forces

Question 13

What kind of biofilm topography is more unstable or prone to sloughing?

Answer 13

Mushroom stacks (when there is high flow and high nutrients leading to rapid growth

Question 14

What kind of biofilm is easier to penetrate ?

Answer 14

Mushroom stacks

Question 15

Why are antibiotic susceptibility tests on bacteria not done on bacteria in suspension?

Answer 15

Because bacteria are 1000x less susceptible in that state

Question 16

What are the molecules used by gram negative bacteria to send signals?

Answer 16

N-Acyl-Homoserine Lanctones (AHLs)

Question 17

How does chain length of the molecules used by gram negative bacteria to send signals, effect signalling?

Answer 17

The longer the chain, the easier the molecule can get through biological molecules

Question 18

Describe theist common method for the destruction of a biofilm

Answer 18

Turbulence, scouring and phagocytes

Question 19

What is native dispersion?

Answer 19

Seems as the terminal stage in biofilm development

Leads to the translocation of bacteria to new sites of colonisation