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Bacterial pathogenesis > Lecture 4 - Adhesion and biofilms > Flashcards

Lecture 4 - Adhesion and biofilms Flashcards

1
Q

What does v.cholera attach to?

A

Attaches to chitin on microplankton/fish

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2
Q

What can bacteria attach to on the host cell

A
  • Epithelia
  • Muscus
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3
Q

What is the difference between G+ and G- bacteria?

A

G+ bacteria

  • thick peptidoglycan layer
  • no outer membrane
  • no LPS

G- bacteria

  • LPS stretches out from the surface
  • Thin peptidoglycan layer
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4
Q

What is S. aureus SasG?

A
  • A cell wall attached adhesin
  • 92nm structure (1/10th length of the bacterium)
  • full of repeat regions
  • long, rigid structure

S.aureus is a major pathogen after surgery

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5
Q

How was it discovered that sasG is important for adhearance?

A
  1. cells were obtained from humans by a swab nasal septum; control was the complement mutant
  2. PBS alone - wouldn’t expect attachment, SH1000 with IPTG (vector w/o sasG) - get some attachement, vector w/o sasG and tetracyclin indution - same level as vector w/o sasG, vector with sasG - high levels of bacterial count, vector with sasG and tetracyclin induction - same level, vector with sasG mutant - lower lever as if no sasG, SasG mutant with IPTG induction - high level
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6
Q

What is GbpA in V.cholera?

A
  • V.cholera is a gram- bacterium
  • GlcNAc (monomer of chitin) binding protein A
  • Bind to N-acteylglucosamine (GlcNAc) and chitin, and the host cells (mucin)
  • multidomain protein
  • Interaction with both chitin (polymer of GlcNAc) and host cells (mucin)
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7
Q

How was GbpA shown to be a vir factor in human disease?

A
  1. Transposon mutagenesis study and screened for phenotype (adhesin to chitin). then rescreeened (as always get a false positive on the first screen) and identified GbpA (focused on this 53kb protein as same size as a protein known from previous work to be involved in adhesion to host cells)
  2. Took a ΔgbpA strain (w/o gbpA coding sequence) and a ΔgpbA, GbpA-His strain. By cloning in the protein, can complement the strain with the protein.
  3. Tested binding to Ht29 cells - showed the attachment % divided by the input number: gpbA mutant attaches less, recomplemented mutant better than wild type
  4. Tested whether gpbA helps binding to other surfaces. Showed that GbpA is a GlcNAc-sensitive chitin binding protein. Looked at
    1. beads coated with chitin (WT binds best, gpbA worse, recomplemented better but not as good as WT
    2. beads coated with GlcNAc, same level as reponse as attachment to chitin
    3. just using purified protein by his-tag. see how much protein was bound to beads after washing. ran western blot to look at levels - GbpA-His protein only one present
    4. competition experiment: shown protein binds to the beads, can it be outcompeted with soluble GlcNAc. Test the specificity of the binding. If have the protein and add soluble glcNAc becomes occupied binding to GlcNAc and won’t observed much binding to beads in western blot. Binding is specific to GlcNAc
  5. suggests that gpbA facilitates binding to GlcNAc or chitin.
  6. Looked at binding in animal experiments with pathogenic bacteria. Used competition index. WT was 1:1 as expected (WT as good as WT). with gpbA mutant had level less than 1 (lowever competitive index) less good at compteting. Therefore the protein is thought to help colonise the mouse.
  7. Also used survival experiments. Number of animals used dependent on three R’s - reduce, replace, refine. showed that gpbA mutant has higher surivial rates.
  8. Also quantified the level of binding of Wt, recomplemented and mutant gpbA to exoskeleton of sea dwelling organisms.
  9. And passive immunisation experiemnts
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8
Q

What is the purpose of adding a his-tag to an expressed protein?

A

6+ repeat of histadine on the c-terminal end of a protein

Used to purify protein on nickel column. Can use in affinity chromatography to purify selected protein.

Or immunotagging

Have to assume that the his tag doesn’t affect the fucntion of the protein - use a cleavable his tag

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9
Q

What is the purpose of a competitive index in an animal experiment with pathogenic bacteria?

A

Wat to test virulence of a pthogen comparative to the WT. Allows a correction of animal variability. Take strains and mix 1:1 (WT:mutant) and input into animal model. What is taken out is the competitive index. If the index is less than one, then the mutant less effective than the WT, higher than 1 means that the mutant is more efficient.

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10
Q

If get a big spread of results in a competitive index using animal experiments with pathogenic bacteria what could this mean?

A

Potentially due to the plasmid not being maintained in all animal equally well. Plamsid can be lost as ti is hard to maintain pressure on the plasmid in an animal system

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11
Q

following the identification of gbpA as a vir factor in vibrio cholera, what was conluded?

A

GbpA may assist in the cyclic transition of v. cholerae between the aquatic habitiat and the human small intestine.

shown that gpbA binds to mucin - may also stimulate mucin production

other toxins involved: TCP: toxin coregulated pillus: essential for v. cholerae to colonise the small intestine. Promotes bacterial aggregation and microcolony formation. Assists in adhesion to the mucosal surface.

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12
Q

What are fimbriae?

A
  • Proteinaceous nonflagellar filaments
  • can be very long structures
  • have to be negatively stained in EM and viewed against a dark background
  • multiprotein complex
  • e.g. In E.coli: Type I fimbriae (encoded by fim operon), Pap fimbriae (pylonephritis associated pili)
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13
Q

Wht fimbriae do E.coli have?

A

Type 1 fimbriae

  • encoded by the fim operon
  • rigid filaments mediating mannose-sensitive hemagglutinastion

Pap-pyloephritis associated pili

functions were attempted to be identified by the isolation of the proteins, by raising gold labelled antibodies to view under EM. Location was identified. This was used to identify the role, which was backed up by mutagenesis screen and purifaction assays

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14
Q

What delivers the Type 1 fimbriae and Pap pilus receptor specificity?

A

Fim H (type 1) or PapG (Pap) adhesin at the top of the fimbriae

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15
Q

How is type 1 fimbriae and pap pilus assembled in the outer membrane?

A

Needs adaptor proteins to attach FimH/PapG to FimA/PapA

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16
Q

Why are type I fimbriae and Pap pilli chaperone-usher fimbriae (pili) (CUP)?

A

Because have ushers anchored in the outer membrane and chaperones to move major subunits though the periplasm and deliver to the ushers to allow assembly.

Ushers: FimD/PapC

Chaperones: FimC/PapD

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17
Q

What are the features of the Fim H adhesin of type I?

A
  • FimH binds to mannosylated uroplakins (specialised bladder epithelials) e.g. can be in complex with oligomannose-3
  • immunoglobulin like fold lacking final beta strand - donated by chaperon
  • Two FimA’s come together and donate a strand to the other subunit, making a stable stucture as FimA links together
  • 40fimA subunits cover 1.5 helical repeats
  • fimH has one operon and one promoter, needs lots of FimA and less of other proteins, achieved by differential mRNA stability
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18
Q

What are the features of the FimH receptor binding pocket?

A
  • lots of aa involved in the interaction to GlcNAc by FimH
  • Make multiple interactions to the sugar via Van del vals forces to give the receptor stability
  • recognises mannose on outside of cells
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19
Q

What factors must be considered when useing mouse models?

A
  • Mouse strain
  • Age of the mouse
  • Procedure archifacts
  • Bacterial innoculum
    • how grown (e.g. PAP doesn’t grow at 30 degrees C)
    • bacterial load
  • Assay/readouts
    • histology
    • bacterial recovery
    • imaging
    • mutant analyses
  • Mouse is not human
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20
Q

What are the challenges of a murine experimental model for UTI and pyelonephritis?

A
  • considerations when working with a murine model
  • Image data interpretation - is it on or in the cell
  • Uretha of the mouse is v small, affects the validity of the experiment. Applied bacteria to the bladder directly using catheter. Possibly damages tissue triggering an immune response which will affect the results
  • Must make sure looking in the right place, the infection may have spread
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21
Q

Why are type 1 fimbriae important?

A

Occur on a lot of different E.coli, very common fimbriae. Very important in bladder infections.

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22
Q

what technique can be used to overcome the 2D image presented using imaging?

A

Use a confocal microscope for 3D image, show whether the bacterium is in the cell, attaches to it, sitting on top

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23
Q

How was it shown that type I adhesion binds mannose?

A
  • Showed that got inhibition of bacterial adhesion to bladder cells by mannose or heptyl alpha-d-mannose.
  • Bacteria were incubated with mannose or heptyl α-d-mannose prior to innoculation. With increasing mannose concentration there was less binding of the bacteria to the bladder cells. Can be competed off with mannose.
24
Q

How was it checked that the bacterial load in the mouse bladder after infection could be reduced through affecting type I mediated adhesion?

A
  • Bacteria incubated with compounds prior to innoculation (different concentration of mannose/surrogate mannose)
  • If add surrogate mannose get no effect but do see a response if add heptyl α-d-mannose which is chemically similar to the substrate in the environment. Also shows slight dose dependence, with additional heptyl… get better response.
25
Q

Outline the complexity of E.coli fimbriae

A
  • Many different fimbrial operons
  • repetoire varies per strain
  • Allelic variants among tip proteins (papG: maybe recognise slightly different sugars or are slightly differently immunogenic - affects how the host responds to E.coli expressing PapG), receptor variation (shared core, different modifications)
  • regulating expression of fimbriae, potential redundancy
  • Coordinated expression
  • May help define tissue tropism
26
Q

Give an exmaple of the complexity of E.coli fimbriae

A
  • E.coli PapGII: globoside - a glycolipid isoreceptor of the human kidney
  • Can have multiple variants of Pap operons per isolate - PapG(tip) has 3 isoreceptor variants
  • In common with Gal (alpha 1-4)Gal; one variant sialic acid residue is added
27
Q

What are e.coli pathotypes?

A
  • Different pathogenic strains of E.coli
  • The diseases that they illicit is due to genome differences, contributed to by pathogenicity islands. Fimbriae (amonst other things) are encoded for on pathogenicity islands.
  • Different pathotypes have extra genomic information.
  • e.g some E.coli cause intestinal diease, some cause extraintestinal diseae (Uropathogenic E.coli (UPEC))
28
Q

How is the expression of fimbriae regulated?

A

By the operon:

  • different levels of the subunit are required (achieved by differential mRNA stablity)
  • environmental control
    • Fim: branched chain aa and alanine (Lrp), temperature, sialic acid, N-acetylglucosamine (NanR, NagC), slyA (virulence factor)
    • Pap: glucose, temperature
29
Q

How are flagella expression and adhesin expression in E.coli said to be a coordinated hieracrhical expression?

A
  • there is a link between Pap and flagella expression. (stick or swim (to kidney cells))
  • One pap is made, flagella are respressed. Downstream of pap expression are flagella expression repressors
  • FIhD transcription master regulator of flagella expression
30
Q

How is fimbrial expression controlled?

A

Randomly (phase variation)

Regulated - indiviually and network

31
Q

What are curli?

A
  • Thin 2-5nm
  • Coiled, highly aggregative
  • produced by a variety of pathogenic and commensal members of the enterobacteriae including e.coli
  • fold into an amyloid fold - similarity in structure to amyloid fibres (neurodegenerative diseases in humans) can be used as a model protein for these eukaryotic proteins
  • transition from monomer to amyloid fibre requires nucleation protein (CsgB)
  • Operon with multiple subunits
  • needs to go through the inner membrane
    • E.coli gram - with sec apparatus, transcript would have a signal sequence to be secreted into periplasm
32
Q

How was curli identified?

A

Binds to congo red, dye that allows colonies to identify bacteria

33
Q

How was it show that curli and cellulose important in biofilms?

A
  • Coordinated curli adhesins and matrix production leads to distinct E.coli macrocolony biofilms
  • Curli and cellulose producing e.coli - structure of the biofilm appears compact in curli- and cellulos producing cells compared to the biofilm of Cellulose deificent e.coli which has an outer starved edge (nutrients at the bottom)
  • Viewed by thioflavin S amyloid-staining fluorescent dye so that both curli and cellulose are stained
34
Q

How do biofilms change the characteristics of a bacterial colony?

A
  • strain genetic background
  • nutrients
  • temperature
  • surface structure
35
Q

What is the relevence of curli in biofilms to pathogenesis?

A

Curli in UTI

Looked at clinical isolates to see if positive for making curli. Saw correlation: some isolates are better at producing curli even at 37 degrees, therefore thought to be associated with survival in the host as strong association with certain diseases

36
Q

How do curli/cellulose impact each others regulation?

A
  • One of the curli proteins directly impacts cellulose regulation and vice versa.
  • There are a multitude of mechanisms feeding into the regulatory pathways of curli/cellulose - ssRNAs, OmpR, 2 component systems
  • all help regulate cellulose and curli, allowing a variety of inputs into the complex network.
37
Q

Outline biofilm formation as a developmental process

A
  1. bacteria attach to the surface (adhesion)
  2. once attached, make into a microcolony
  3. grow and potentially create a highly complex system (macrocolony)
  4. matrix-dispersal
38
Q

Define a biofilm

A
  • A microbially derived sessile community
  • typified by cells that are attached to a substratum, interface or to each other
  • embedded in a matrix of an extracellular polymeric substance
  • exhibit an altered phenotype with regard to growth, gene expression and protein production.
39
Q

What is sociomicrobiology?

A

Greenberg. What bacteria can achieve together. Uses p. aeruginosa as model system.

40
Q

How can you show experimental that a matrix is present (Biofilm not collection of cells)?

A

Multi photon laser scanning microscopy, confocal microscopy

TEM/SEM: bad because samples are dried out and hard to interpret, what is the relevance of the structure

41
Q

Why has their been a dramatic increase in biofilm research?

A
  • Awareness
  • Clinicians involved
  • Technological advances (e.g. advanceing in imaging, Gfp and derivatives)
  • Trends in science
  • Funding
42
Q

How was it shown that quorum sensing is important in p.aeroginosa?

A
  • O’Toole. Used an in vitro assay amenable to mutant screens in a 96 well plate. Bacteria were stained when they adheared to the surface and mutants showed lack of adhearance.
  • Bad: static biofilm, limiting nutrients
  • Quantify by resolubilising crystal violet and do OD measurement
  • Used flow cells to test biofilms -

e.g. Identified P aerogeinosa biofilm regulator, LadS from a Tn5 mutant library = polysaccharide matrix regulator

without quorum sensing the biofilm was flat

43
Q

How did friedman and kolter show that Alginate is not a key component of P aeruginosa biofilm matrix?

A
  • Used a different assay.
  • Used PA14 strain and algD grew for 24hr in rich media
  • Formed a static biofilm for algD mutants, not for pelA mutants
  • Shows that biofilm formation is a diverse and regulated processes
44
Q

What is the process of flow cell?

A
  • constant nutrient replenishment
  • not high throughput
45
Q

How did Hentzer show that Alginate is a key component of P aeruginosa biofilm matrix?

A

Took two strains, PAO1 and PDO300 (algS - alginate overproduction strain) grew in flow culture for up to 5 days. WT strain forms a dense biofilm. Aginate overproduction strain becomes structured.

46
Q

What is the divergent evidence regarding the importance of quorum sensing in biofilms?

A

Is important

Davies used P.aeruginosa (PAO1) grown in the presence of glucose. lasl mutant did not form ‘mature’ biofilms

Isn’t important

Heydorn showed growth of (PAO1) with citrate up to 98 hours and no difference in biofilm formation.

therefore is the difference in type of biofilm dependent on the carbon source?

47
Q

How was it shown that biofilms have physiological heterogeneity?

A
  1. Industrial Pa isolate ERC1 grown in drip-flow culture system with gluose on stainless steel for 96 hours. In:
    • A) high phosphate media
    • B) High phosphate switched to low phosphate media
  2. As a result of the low phosphate an enzyme in the biofilm at the top layer was upregulated and the top layer was metabolically diffferent to the middle layer.
  • Stained using propidium iodide stain (DNA)
  • grown in a fluoregenic Alk Phos substrate
48
Q

How were biofilm factors identified in uropathogenic E.coli?

A

Mutant screen for biofilm factors in E.coli (uropathogenic)

Found that adhesins are an important part of biofilms

  • 45000 transposon mutants
  • screened 6.144 for biofilm formation in three conditions
  • 243 had a biofilm defect upon rescreening = 55 false positives
  • 63 deficient under all conditions, more under just two
  • mapped 40 loci
  • found type 1 and curli mutants, defective in 2 out of 3 conditions
49
Q

How was the spacial proteome of intact biofilms analysed in situ?

A
  • Used matrix assisted laser desorption/ionization (MALDI) time-of-flight imaging mass spectrophometry (IMS) to analyze the spacial proteome of intact biofilms in situ
  • Looked at the interface between liquid and air, looked for proteins in that area.
  • Saw a spacial difference in expression of type 1 and curli, exhibited the role of oxygen.
50
Q

What % of human bacterial infections involve biofilms

A

65-80%

Structured community of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface

51
Q

What is the interaction of the bacteria and host in clinical biofilms?

A

During bacterial biofilm growth, bacteria signal to the host and the host responds, modifying bacterial behaviour. DNA has been found to be part of the p. aeruginosa matrix of cystic fibrosis patients - developed a inhaler with a DNA protease to break down the biofilm.

Occur on medical devices, tissues

52
Q

Give examples of the locations in the body and bacteria that form infections associated with biofilms?

A
  • Ear: Otitis media (diverse, H.influenzae)
  • Stents
  • Chest: Cystic fibrosis (P. aeruginosa, B. cepacia)
  • Urinary and other catheters (bladder infection, kidney infection)
  • Sutres
  • Chronic wounds
  • Prosthetic devices
  • Native valve endocarditis (diverse; S. aureus, Streptococci)
  • Peridontitis (diverse, lactobacilli, b. gingivalis)
53
Q

How is the ROS response triggered in p. aeruginosa infection?

A
  1. LPS signals through TR4 by the attachment of P.aeruginosa, which signals to the host for pathogen associated molecular mechanisms
  2. airways become inflamed
  3. toxins produced
  4. alginate triggers an antibody response
  5. ROS response to attack bacteria
54
Q

What is the problem of applying kochs postulates to biofilms?

A
  • Chanllenge to culture the pathogen in the lab if it needs to be attached to a substrate
  • May occur as part of a poly microbial infection
55
Q
A

Bacterial pathogenesis (8 decks)

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