Biofilm

Question 1

What is the definition of a biofilm?

Answer 1

• “functional consortia of microbial cells bound to and growing at an interface. Such consortia are generally enveloped within extracellular polymers - SLIME”
• Individual cells within a biofilm are physiologically distinct from their planktonic counterparts
• very variable

Question 2

When do biofilms grow?

Answer 2

• Biofilms grow when microorganisms attach to surfaces and grow
• immediate phenotype change (physiology change)
• deposition of slime within minutes (glycocalyx / matrix)
• Matrix helps to moderate the physico-chemical environment of microorganisms
• leads to microcolony formation, high cell density (cells are in close proximity with one another)
• single or multi species
• bacteria, yeasts, algae, fungi, protozoa

Question 3

What charge does slime generally have?

Answer 3

• negative charge
• Anything that wants to get in has to moderate THROUGH the slime – restrictive
• Thick slime = electrochemical gradient of nutrients going into the core of the cell

Question 4

What do biofilms provide?

Answer 4

• protection from desiccation
• protection from phagocytes
• concentration of nutrient and cations
• provides for localised high cell density
• concentration of extracellular products
• interspecies cross-feeding
• physiological capacity of biofilm is greater than that of its component organisms

Question 5

Why is it hard to penetrate the slime ?

Answer 5

• It is a hydrated layer protecting the cell (almost like hydrogel)
• phagocytes have difficulty penetrating
• high cell density - ‘packed in like sardines’
• breakdown products are used by other species

Question 6

Where do we find biofilms?

Answer 6

• dental plaque
• skin (natural barrier)
• damaged skin (opportunistic pathogens)
• staphylococcal infected skin ulcer
• indwelling devices
• Endocardial Pacemaker Lead
• internal surfaces

Question 7

What is the importance of biofilms?

Answer 7

• Biofouling (air con, pipes, heat exchangers)
• Biocorrosion
• Biodeterioration / spoilage
• Bioremedioration
• Infections of soft tissues (pathogenesis)
• Infections associated with indwelling medical devices (pacemakers, CNS shunts, catheters etc)
• water treatment
• resistance (antimicrobials, host defences)

Question 8

Why is biofilm resistance an issue?

Answer 8

• Positively charged antibiotics cannot penetrate as biofilms are negatively charged (exclusion)
• Pockets of cells within biofilm.
• Greater electrochemical nutrient gradient the deeper embedded the cell
• Cell-cell signalling: cells communicating through low molecular weight diffusible materials. Upregulating key genes that may enhance the properties of the organisms growing within the biofilm

Question 9

What is cell-cell signalling?

Answer 9

• small, diffusible chemical signals
• Autoinduction: when the products being produced by the first organism upregulate key genes within the producing organism
• Alloinduction: when products being produced by one type of organism upregulate genes in an unrelated species
• up-regulate target genes
• ## coordinate population response (quorum sensing)

Question 10

Steps in Biofilm formation (6)?

Answer 10

• arrival at surface
• irreversible attachment to that surface
• adoption of sessile phenotype
• biosynthesis of exopolymers
• up-regulation of production of extracellular factors (virulence factors etc)
• detachment and dispersal

Question 11

Describe the different ‘mechanisms’ that occur during the arrival at the surface stage of biofilm formation

Answer 11

• diffusion: if bacteria is not mobile – in static fluid environment – random diffusion (collision)
• Active motility: if bacteria has flagellae, going towards some nutrients etc
• Turbulence = more collision probability

Question 12

What forces are included in the attachment to the surface phase?

Answer 12

• Van der Waals forces of attraction (gravity)
• electrostatic forces (repulsion/attraction)
• reversibly bound

Question 13

What is irreversible binding?

Answer 13

• primary minimum
• bridging structures
• energy required to overcome energy barrier

Question 14

What happens after irreversible binding?

Answer 14

• binding reinforced
• environment modulated
• phenotypic (QSTA) switches
• upregulating exopolymer production: cementing cells to the surface and each other
• allowing community to develop

Question 15

What does EPS (extracellular polymeric substances) deposition bind?

Answer 15

• cells-cells

- cell-substratum

Question 16

What is micro-colony formation?

Answer 16

• Growth and multiplication leads to microcolony formation (small pockets of cells = microcolonies)(3D growth)
• establishment of gradients
• starvation responses
• microcolony becomes a biofilm

Question 17

What are the 3 types of biofilm phenotype?

Answer 17

• corn cob (most common, found in the mouth on teeth - dental plaque)
• mushroom (more aqueous)
• plaque (mass)

Question 18

What does biofilm phenotype depend on?

Answer 18

• varies on nutrient environment

- can change biofilm type by changing the turbulence etc

Question 19

What are flow channels?

Answer 19

A route of entry through the biofilm

Question 20

Describe successional development (e.g. plaque formation)

Answer 20

Successional development = build up of organisms
A) colonising a surface that like the nutrients on the surface
B) secondary organisms attach themselves to the first group
C) more and more
D) bridging organisms
E) secondary colonisers

Question 21

Describe the 3 different types of dispersal of biofilm

Answer 21

• Starvation: nutrient deprived – starvation response: production of metabolites that let organisms survive - lyase enzymes that eat away at the exopolymer (slime)
• Physical Sloughing – shear force releasing clumps of cells
• Cell cycle mediated erosion: release of single cells