micro 3 (CF) Flashcards by Sarah Ramsbottom

CFTR?

cistic fibrosis transmembrane regulator protein

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How many mutations are there in the CFTR protein?

> 1,800

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What is the most common mutation on the CFTR protein in CF?

Phe 508 del

> 80%

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What does CFTR protein do?

allows Cl- ions to be secreted into the airway surface liquid

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What happens in Phe508del CF?

CFTR protein is absent
Cl- ions can't be pumped out 
airway surface liquid dehydrates
mucus attracted to cell surface
cilia can't beat properly
mucus becomes stuck
inability to clear bacteria - infections

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4 conventional CF pathogens

P aeruginosa
S aureus
H influenzae
B cepacia complex

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emerging CF pathogens

Stenotrophomonas maltophilia
MRSA
M. abscessus
Achromobacter spp
Streptococcus milleri/anginosus group
Aspergillus fumigatus (Fungus)

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What are the initial pathogens that cause CF infections?

H influenza

S aureus

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What pathogens do CF infections progress to?

P aeruginosa

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How to reduce cross infection in CF?

cohort segregation (same bacteria)
individual segregation
personal hygiene and PPE

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What is the 1st bacteria to colonise the CF lung?

staphylococcus aureus

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2 subtypes of S aureus in CF infections?

MRSA

small colony variants (SCV)

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describe small colony variants?

small colonies when grown on agar
< 1mm
non-pigmented
non-haemolytic
biochemical tests for ID might not work

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What kind of metabolism do small colony variants have?

altered metabolism or auxotrophic

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When do wild type change to small colony variants?

when stressed - antibiotics

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What small colony variants have the strongest association with lung function?

SCVs that are thymidine dependent

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What happens in children with S. aureus SCVs?

they have lower mean % of predicted FEV1

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What is Pseudomonas aeruginosa?

G- facultatively anaerobic bacillus

usually an opportunistic pathogen

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Where is Pseudomonas aeruginosa found?

UTIs
sepsis
non-CF lung infections
GI

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What does Pseudomonas aeruginosa have multiple of?

efflux systems

secreted and cell based virulence factors

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How many CF patients have Pseudomonas aeruginosa by age of 20?

> 50%

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Specialised strains of Pseudomonas aeruginosa associated with CF infection

Liverpool epidemic strain (LES)
Midlands1
Manchester epidemic strains
DK2 in Denmark
Aust-02 in Australia

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How to eradicate PA infections?

combination of oral/IV and inhaled antibiotics

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What is chronic colonisation with PA associated with?

worse lung fxn outcome

higher inflammation

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What does PA have to overcome in the CF lung?

protection from the immune system | less oxygen in the mucus layer

What are changes in PA to adapt to CF lung regulated by?

quorum sensing

What is quorum sensing?

Ability to detect and respond to cell population density by gene regulation Expression or repression of specific genes which produce phenotypes which will be beneficial

What 3 characteristics do bacteria need to use Quorum sensing?

- Ability to produce a signaling molecule (an autoinducer) - Be able to detect the change in signaling molecules - Regulate gene expression as a result

How can PA use quorum sensing?

Biofilm formation | EPS production

What is T3SS?

needle like machinery that lets bacterial effectors | translocate directly into the cell

What does T3SS cause?

Causes tissue injury and cytotoxicity

How many T3SS dependent effectors does PA have?

PA 4 T3SS dependent effectors?

ExoS ExoT ExoY ExoU

Which T3SS effectors disrupt host cell cytoskeleton?

ExoS, T and U

What can ExoU do?

cleave phospholipases (leads to cell death)

How does T3SS activate immune response?

via IL-1 beta

What do chronic PA infections do with T3SS?

they select against T3SS expressing PA | patients have antibodies against T3SS effector proteins

What is LPS a major component of?

G- outer membrane

What antigen of the outer membrane is lost in early CF infections?

O antigen

What is modified/changed in the OM in CF?

lipid A structure

What residues are acquired in early CF when lipid A is modified?

pamitate and aminoarabinose residues

What is aminoarabinose associated with?

increased resistance to antimicrobial peptides and some antibiotics

What do LPS modifications cause?

they make PA less visible to the immune system

In what bacterial infections is bacteria free floating?

acute infections

What is free floating bacteria called?

planktonic

How are bacteria attached in chronic CF infections?

attached to surface and become embedded in acellular matrix

What happens when bacteria is embedded in acellular matrix?

surface of epithelial airway is damaged

What is in the matrix of PA infections?

alginate PEL PSL extracellular DNA

What type of communities are biofilms?

polymicrobial | have different micro-environments

1st identified bacteria in biofilms

What other bacteria can cause biofilms?

B cepacia complex

What do biofilms result in?

x1000 increase in resistance to antibiotics

5 stages of biofilm formation in chronic CF

1. initial attachment 2. irreversible attachment 3. microcolony formation 4. maturation 5. dispersion

What is needed for irreversible attachment of biofilm?

flagella | type IV pili

What is produced in microcolony formation stage of biofilm formation?

production of EPS

What is formed in maturation stage of biofilm formation?

formation of 3D complexes | creates oxygen gradient (anaerobic in centre)

What can PA switch from and to in chronic infections?

switches from non-mucoid to mucoid phenotype

What causes PA to switch to mucoid?

large amounts of alginate produced

What do rugose SCV use as structural components in biofilms?

use Pel and Psl as structural components

What can Pel do?

crosslink extracellular DNA in PA biofilm matrix

What is alginate?

linear polysaccharide | negatively charged

How is alginate initially produced?

homopolymer of D-mannuronic acid residues

What is alginate modified by?

enzymes - AlgI, AlgJ, AlgF

What is alginate epimerized by?

AlgG

What does AlgG convert D-mannuronic acid to?

L-guluronic acid

What is Psl?

neutral pentasaccharide repeat | contains glucose, mannose, and rhamnose

What is Pel?

cationic amino sugars 1→4 linked partially acetylated galactosamine and glucosamine sugars

How does PA invade complement?

produces enzymes

What enzymes does PA produce and what do they do?

alkaline protease and elastase | degrade C3b

What is downregulated by PA?

flagellin and T3SS

2 other CF pathogens

1. Burkholderi cepacia complex (BCC) | 2. non tuberculosis mycobacteria

How many species of BCC?

3 types of BCC species?

B cenocepacia B multivorans B dolosa

What 2 complexes are NTM isolates in CF from?

mycobacterium avium | mycobacterium abscessus complex

What species does mycobacterium avium include?

4 M avium species and M intracellulare