Biolfilms Flashcards
What are biofilms?
Structured microbial communities embedded in a self-produced matrix that attached to surfaces or each other
What makes up the self-produced matrix?
- Polysaccharides
- Proteins
- DNA
- B-glucans (fungi)
Where do biofilms form?
Both on biotic (e.g. host tissues) and abiotic (e.g. pipes, devices) surfaces
What are the four main stages of biofilm formation?
- Initial attachment
- Irreversible attachment
- Microcolony formation
- Maturation
- Dispersal
What is the initial attachment stage of biofilm formation?
Initial attachment to surface (reversible)
No permanent chemical bonds yet, just intermolecular forces
What are the key features involved in attachment?
Adhesins
Organelles like pili (for initial adhesion) and flagella (for movement to surface)
What is the irreversible attachment stage of biofilm formation?
When gene expression changes in the microbe, and adhesion become permanent
What happens when gene expression changes (during irreversible attachment)?
- Production of extracellular polymeric substances (EPS) beings
- Secretion of “sticky” polysaccharides
What is the microcolony formation stage?
Formation of an early biofilm.
Cells start dividing and clustering, with microcolonies forming.
Start of nutrient channels
When does quorum sensing begin in biofilm formation?
Probably throughout, but quorum-sensing molecules accumulate during microcolony formation.
These molecules help co-ordinate behaviour (wrt gene activation and matrix production)
What are quorum sensing molecules called?
Autoinducers
What is biofilm maturation?
Where the biofilm architecture is markedly complex and structured
What are some structural features of mature biofilms?
- Mushroom-shaped towers with water/nutrient channels between them
- Diversification of cell phenotypes dependent on location within the biofilm
- Matrix becomes thicker and more protective
How are cells in mature biofilms phenotypically heterogeneous?
- Outer cells = nutrient access = faster metabolism
- Core cells = less nutrient access = slower metabolism, but higher resistance (persister cells)
What are persister cells?
Subpopulation of non-growing/very slow-growing cells, which have a much higher tolerance to antibiotics & immune clearance. They are not genetically resistant mutants
How do biofilms promote persister cell formation?
Inner cells often have stresses like low nutrient and oxygen (hypoxia) access, which drives the formation of persister cells
What is the impact of persister cells?
Explains why biofilm-associated infections have high relapse rate after antibiotic treatment.
Even if most bacteria are killed, dormant persisters can survive and restart infection
What is the structure of C. albicans biofilms?
Dense hyphal filamentous structure
What is biofilm dispersal?
Where some cells detach and return to planktonic state
What are the different types of dispersal?
- Active dispersal (enzymatic breakdown of matrix)
- Passive dispersal (by mechanical forces like blood flow)
What are some dispersal triggers?
- Nutrient limitation within biofilm
- Accumulation of waste products
What are the properties of dispersed cells?
- Highly virulent
- Often more resistant than original planktonic cells
What are 3 different advantages of biofilms?
- Protection & persistance
- Metabolic cooperation
- Easy gene transfer
Are biofilms single species?
Biofilms can be single species, but is more commonly multi-species
