Biofilm Flashcards
What is the definition of a biofilm?
- “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
When do biofilms grow?
- 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
What charge does slime generally have?
- 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
What do biofilms provide?
- 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
Why is it hard to penetrate the slime ?
- 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
Where do we find biofilms?
- dental plaque
- skin (natural barrier)
- damaged skin (opportunistic pathogens)
- staphylococcal infected skin ulcer
- indwelling devices
- Endocardial Pacemaker Lead
- internal surfaces
What is the importance of biofilms?
- 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)
Why is biofilm resistance an issue?
- 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
What is cell-cell signalling?
- 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)
Steps in Biofilm formation (6)?
- 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
Describe the different ‘mechanisms’ that occur during the arrival at the surface stage of biofilm formation
- 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
What forces are included in the attachment to the surface phase?
- Van der Waals forces of attraction (gravity)
- electrostatic forces (repulsion/attraction)
- reversibly bound
What is irreversible binding?
- primary minimum
- bridging structures
- energy required to overcome energy barrier
What happens after irreversible binding?
- binding reinforced
- environment modulated
- phenotypic (QSTA) switches
- upregulating exopolymer production: cementing cells to the surface and each other
- allowing community to develop
What does EPS (extracellular polymeric substances) deposition bind?
- cells-cells
- cell-substratum
What is micro-colony formation?
- Growth and multiplication leads to microcolony formation (small pockets of cells = microcolonies)(3D growth)
- establishment of gradients
- starvation responses
- microcolony becomes a biofilm
What are the 3 types of biofilm phenotype?
- corn cob (most common, found in the mouth on teeth - dental plaque)
- mushroom (more aqueous)
- plaque (mass)
What does biofilm phenotype depend on?
- varies on nutrient environment
- can change biofilm type by changing the turbulence etc
What are flow channels?
A route of entry through the biofilm
Describe successional development (e.g. plaque formation)
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
Describe the 3 different types of dispersal of biofilm
- 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
