10. Biofilms

Question 1

Define biofilms.

Answer 1

Biofilms are aggregates of microorganism in which cells that are frequently embedded within a self-produced matrix of extracellular polymeric substances (EPSs) adhere to each other and/or to a (biotic or abiotic) surface. Biofilms is often the natural state of bacterial life.

Question 2

How does biofilm impact human life?

Answer 2

Food, food handling, packages.

Equipments, pipes, (chronical source of microbial contamination)

cause of fuel consumption in marine

probiotics

immobilized cells

Reduce heat transfer (consume energy)

Cleaning of waste water

drinking water pipelines

corrosion

infection

medicine

Question 3

Which 6 forces promotes adhesion+

Answer 3

• Van der Waals interaction (always attractive between bacteria and surface, depend on the materials and geometry of the studied system, e.g. very high for metal surface) The more metallic surface the vdw forces is quite big but are still important on different surfaces.
• Electrostatic double layer interaction (commonly repulsive force since most natural surfaces are negatively charged, so bacteria, strongly dependent on the ionic strength of the liquid environment)
• Sterically interaction (commonly repulsive for bacteria-surface interaction due the action of surface-grafted polymers)
• Hydrodynamic interactions/hydrophobic interactions (forces of entropic origin due displacement of water molecules, can be both attractive or repulsive)
• Depletion interactions (forces of entropic origin due to displacement og e.g. soluble polymeric molecules, mainly attractive) Similar to hydrodynamic interaction.
• Gravity (can be attractive or repulsive, often important in microbiological experiments)
  these types of interactions are commonly very short-ranged, which for bacteria-surface interactions means <100 nm separation, however they can be very strong at short separations (>10nm) and thus play an important role in maintaining bacteria surface-bound.

Question 4

What kind of interaction can happen between the bacteria

Answer 4

Specific interaction – stereospecific biomolecular interaction that govern bacterial surface adhesion.
Involve complementary (macro)molecules, common in adhesion to biotic surfaces, e.g. colonization of tissue or plants. Bacteria carry adhesins, typically lectin (protein that bind carbohydrates with high specificity) that bind to cell receptors, e.g. on endothelial cells.

Structures on the microbe important for specific surface interactions.
glycocalyx – extracellular polysaccharides or glycoprotein in sticky network. Capsule – district, gelatinous glycocalyx. Slime layer – irregular, diffuse layer. Also involved in nonspecific adhesion.
LPS gram- bacteria
Lipoteichoic acid (B) and teichoic (A) Gram+ bacteria. Teichoic means “wall”. Other adhesins, such as surface proteins, glycol- and lipoproteins. Fimbriae (pili) (passive structures) type 1 (mannose specific) in both E. coli and salmonella P-pili. Several others.
Flagella and type IV-pili (actively modulated structures).

Question 5

How can blocking effect the biofilm?

Answer 5

Testing and proving bispecific interactions by specific blocking.
A general way to test/prove specify is to add free ligand or receptor to test solution and this way block specific interactions. Important to consider the effect of multivalent interactions (i.e. a single bacterium can form several receptor-ligand bonds.

Blocking salmonella adhesion with mannan-oligosaccharides (MOS) – currently used functional MOS extracts from saccharomyces cerevisiae cell wall. Large scale use of MOS within the poultry industry for the control of salmonella. MOS can significantly reduce the colonization of salmonella typhimurum in chick even under large challenge conditions.

Question 6

How is flagella and pili effect by biofilm

Answer 6

Flagella and type IV-pili enhanced surface colonization by enabling surface exploration.
These are restively large (compared to the bacterial body) structures – increased binding probability due to larger interaction volume. Both flagella and type IV pili provide surface mobility – allow more efficient colonization since bacteria can explore the surfaces and expand the biofilm laterally. Flagella enable bacteria to “swim along surfaces. Type IV pili allow bacteria to crawl and “walk along surface cues.
Type IV-pili mediated mobility support “social self-organization” among P. aeruginose

Fimbriae (pili) are passive surface appendages that mediate surface adhesion.
Fimbriae are passive structure, much smaller than flagella and type IV pili, but numerous. Many gram- bacteria have pili that are structurally similar often presenting a lectin at its tip. Most common is type 1 fimbriae (e. coli, salmonella, P. eurugimosa.)

Question 7

How does Fimbriae promote biofilm?(4)

Answer 7

Fimbriae promote biofilm formation by:
Fim+ stick move stick -> when increased flow they stick, fim- stick and wiggle.

• mediating specific and non-specific surface bonds.
• enable bacteria to move along surfaces (compared action of actively modulated flagella and type IV pili)
• Provide bacteria force-enhanced binding strength, which protect bacteria from being rinsed off a surface under harsh conditions.
• Stabilization of bacterium interaction.

Question 8

How do bacteria know that there ate on a surface

Answer 8

pH
Feels that there is a concentration difference on different sides. Increasing concentration closer to surface.

Osmolatilty
Similar as pH

Flagella inhibition
The flagella can’t move and that shows the cell that something is there.

Question 9

How can you get away with biofilm

Answer 9

Strategy to clean the biofilm à a breakdown of EPS, b disables the bacteria ß often chemically isn’t enough.

Strategies to reduce biofilm formation on surfaces.
Incorporate and/or release antibiotics from material surface coatings

Drawback: this will push development of antibiotic resistance. As alternatively silver nanoparticle or antibacterial peptides (AMPSs) can be used, which are to some extent better with respect to development of resistance. Many surface coatings working by “controlled release action” tend to have reduced efficiency over time.

Alternative treatments that interfere with cell signalling involved in phenotype change to the biofilm state such as control molecules that target quorum-sensing mechanisms of the bacteria would be preferable, however these strategies are not yet developed.
Design surfaces to prevent bacterial adhesion and growth
- Geometric factors (roughness, voids)
- Chemical coatings (e.g. PEG, Heparin, quaternary ammoniums, Ag, mixed noble metals)
Not all type of surface adhesion will support biofilm formation

Question 10

What is some important characteristic of a bacterial biofilm

Answer 10

Heterogenous structure. Different bacterial genotypes/phenotypes depending on position (bacteria organize and acquire different functions). Besides bacteria, a biofilm is composed of extracellular polymeric substances (EPS) (mostly sugars) which are carbohydrates => SLIME. Biofilms also contains extracellular DNA.