Lecture 5 Flashcards
What are biofilms?
- Conditioning firm of organic and inorganic particles
- Bacteria arrive on surface
- Bacteria attach (reversible/irreversible)
- Biosynthesis of matrix
3 ways bacteria bind to surface
Diffusion
Motility chemotaxis
Turbulence impaction
Arrival of bacteria to surface layers
- Flow of fluid or air
- Boundary layer (no flow)
Surface
laminar flow
Bacteria on separate layers
The boundary layer is not affected (no flow)
Turbulent flow
Lots of mixing between bacteria
Boundary layer disturbed
How is turbulent flow made greater
Rough surfaces
Brownian movement
30-100nm from surface as negatively charged surfaces repel
Bridging structures
Generic adhesions - flagella, fimbriae, pili, stalks, teichoic acids
Are brownian movement and bridging sturctures reversibly or irreversibly bound?
Reversibly bound
Name generic adhesions
Pili, fimbriae, flagella, teichoic acids etc
Bind specifically or non-specifically
Specifically - pathogenic bacteria, some non-pathogenic bacteria, mainly glycoprotein receptors
Non-specifically - Electrostatic forces (abiotic surfaces + conditioning film)
What are teichoic and lipoteichoic acids made of?
Fibronectin - Glycoprotein (mannose)
What do flagella bind to?
Toll-like receptor 5
What specific sugars are found in glycoprotein receptors
Mannose - Vibrio chloerae, Escherichia coli
Galactose - Neisseria gonorrhoeae, Bordetella pertussis
Fucose - Vibrio cholerae
Glucosamine - Neisseria gonorrhoeae
What are attachment proteins?
- Sugar-binding proteins
- Encoded in plasmids
- Sugar residues in host receptors - glycans, glycoproteins, and glycolipids
What are the attachment proteins for Yersinia, Salmonella, and Neisseria?
YadA
SadA
NadA
Attachment proteins for E. coli and Haemophilus influenze?
Hia and Hsf proteins
EibA-G protein
Gram positive attachment proteins
Group A Streptococci - Protein M
S. aureus - protein A
C. difficile - CbpA
Name examples of irreversibly bound bacteria to surface mechanisms
Phenotypic switch
Exopolymer deposition
Cemented
Reversible to irreversible attachment
- Attachment and adhesions form clusters
- Cell communication after enough cells have clustered
- alg - Important gene
- Over-secrete alginate to form slime
- Cements cells to surface
- Mature Biofilm forms via in-house division
Cell-cell signalling
Synthesis -> Recognition -> Response
Gram +ve - Oilgopeptides used
Gram -ve - AHLs or HSLs used
N-Acyl-Homoserine Lactones types
OHHL (OC6) - Erwinia and Yersinia
BHL (C4) - P. aeruginosa
OdDHL (OC12) - P. aeruginosa
Cell signalling in same species cells
Low HSL conc
Below threshold conc
No co-ordinated response
High HSL conc
Above threshold conc
Co-ordinated response
Other name for threshold density
Quorum
What does Allvibrio and Photobacterium fisheri show?
Bioluminescence
What do LuxR and LuxI encode?
Regulatory genes
LuxR - Activator proteins
LuxI - HSLs
Promoters for both operons
What does Lux A-E encode for?
Structural genes
Light production
What do LuxI operons cause
- When sessile, 50-60 changes in gene expression
- Down-regulation of planktonic genes
- Up-regulation or new expression of beneficial genes e.g. extracellular polysaccharides, antibiotic production, virulence factors
What are some species with LuxI/LuxR homologues?
- Vibrio cholera
- E. coli H2
- P. aeruginosa
What is a mature biofilm matrix made from?
~98% water
~2-5% cells
Exopolymeric substances
Absorbed materials - Nutrients, waste
Biosynthetic microbial polymers - Extracellular polysaccharides, nucleic acid, proteins, glycoproteins, phospholipids
What do exopolymeric substances do?
- Cellular cement
- Form matrix framework
- Provide structure
- Defined architecture to biofilms
Where is there higher bacterial growth and EPS production in biofilms?
Layers closer to nutrients
Biofilm topography
- Low flow rate
- Slow growth, compact
- Most biofilms
- High flow rate
- Rapid growth, prone to sloughing
- Unstable
Sloughing
Turbulence, scouring and direct or indirect grazing of biofilm
Programmed detachment
- Synchronised liberation of daughter cells
- More hydrophilic
- Down regulation of high mwt LPS
- Leaves low mwt LPS
- Shot out of the biofilm
- 2-3 division before attachment
What are cells embedded in biofilm matrix protected from?
- Desiccation
- Starvation
- Poisoning
- Predation
- Colonisation
Are bacteria close in biofilms
Yes, with pooled extracellular enzymes and greater resistance to antimicrobial compounds
Why are biofilms more difficult to kill?
- Stress tolerance
- Less diffusion in matrix
- Can require 1000x high conc of antimicrobial agent
