Chronic Infection Flashcards
P.aeruginosa can form biofilms where?
On abiotic surfaces or on biotic surfaces
What regulatory switches control biofilm production?
Gac/Rsm cascade
c-di-GMP signalling- high c-di-GMP
What are the features of chronic infection?
T6SS highly active Sessile T3SS not very active Exopolysaccharide production Not many virulence factors being produced
What is required for biofilm formation?
Flagella, Type IV pili, cup fimbriae and adhesins
Production of exopolysaccharide
What is needed for biofilm attachment to surfaces?
Flagella, type IV pili, cup fimbriae, adhesins
What exopolysaccharide is produced in the mucoid biofilm phenotype?
Alginate
What exopolysaccharides are produced in the non-mucoid biofilm phenotype?
Pel
Psl
What dye binds to exopolysaccharides?
Congo red
What is the process of biofilm formation?
1) Transport to the biotic/abiotic surface via flagella
2) Attachment to the biotic/abiotic surface via flagella, type IV pili, adhesins, cup fimbriae
3) Motility on the surface and mushroom formation via type IV pili
4) Biofilm maturation via exopolysaccharide production: Production of alginate, psl, pel, eDNA
4) Dispersal: Breaking down the exopolysaccharides and cleavage of adhesins… glycoside hydrolase and alginate lyase
What is needed for mushroom formation?
Type IV pili
What is needed for breaking down of the exopolysaccharide?
Enzymes
Alginate lysase
Glycoside hydrolase
What is needed to break down alginate?
Alginate lyase
What is needed to break down pel/psl?
Glycoside hydrolase
How do biofilms protect the bacteria?
Makes them much more antibiotic resistant as it is harder for antibiotics to penetrate the biofilm
Makes it harder for the bacteria to become phagocytosed
Exopolysaccharide associated with mucoidy?
Alginate
What exopolysaccharide is primarily produced by P.aeruginosa in CF patients?
Mucoidy biofilm phenotype- alginate
What is the importance of the T6SS with relation to biofilms?
During biofilm formation is is possible that other bacterial species may enter the biofilm and benefit from its protective environment. The T6SS is therefore beneficial in killing these cells which may compete for nutrients etc
How does the T6SS work?
There is a contractile sheath which reveals a nanotube- able to penetrate the target bacterium
In acute infection how does the input environmental strain compare to the output strain?
Not many differences
There are hardly any genetic differences
There was no time for differences to be accumulated as there is no persistence
In chronic infection how does the input environmental strain compare to the output strain?
There are may genetic differences
The bacteria are persisting in chronic infection and have therefore had time to evolve and develop mutations that have been selected for
They acquire pathoadaptive mutations which help them to survive in the environment
Chronic infection is very common in?
CF patients
What are the typical types of pathoadaptive mutations acquired in chronic infection?
- Loss of motility
- Increase in mucoidy
- Loss of T3SS
- Increase in T6SS
- Loss of virulence effectors
- Loss of QS
- Increased antibiotic resistance
What mutation leads to sessility?
Mutations in rpoN
What mutation increases antibiotic resistance?
Mutations in muxZ
What is MuxZ?
Negative regulator of an efflux pump
How do mutations in muxZ increase antibiotic resistance?
MuxZ is a negative regulator of an efflux pump
Therefore, mutation in muxZ will increase the capacity of the bacteria to expel any drugs or antibiotics that enter
Increased antibiotic resistance
What is mucA
Anti-sigma factor
Mutations in mucA lead to?
Increased alginate production and mucoidy
Mutations in mucA are typically?
Loss of function mutations
How does a mutation in mucA increase alginate production?
AlgU leads to alginate production
MucA is able to sequester AlgU and reduce the amount of alginate produced
Therefore mutations in mucA increase alginate production
What is algU?
Alternative sigma factor
What do mutations in retS cause?
Hyperbiofilm phenotype
Increased c-di-GMP levels
What is RetS?
Negative regulator of Gac/Rsm signalling
What do mutations in lasR result in?
Loss of QS system
What is LasR?
Transcriptional regulator
The master quorum sensing regulator
What is rpoN?
Alternative sigma factor
Summary of all the mutations?
mucA loss of function retS loss of function rpoN mutations mexZ mutations lasR mutations
Why do contingency mutations arise?
Mutations often have a cost involved. Contingency mutations allow the phenotype/effect of a prior mutation to be reverted
Why might a contingency mutation for increased alginate production occur?
As increased alginate production is a very energy costly process
What is the contingency mutation to the loss of function mucA?
Mutations in algU
What contingency mutations are there to the retS mutation?
Mutations in gacA, gacS, rsmA
How can strains evolve quickly?
Mutations in mutS and mutL
What are mutS and mutL involved in?
They are involved in mismatch repair
Mutations in mutL and mutS result in?
The incorperation of more mutations as fewer mutations are fixed/resolved
