C5- Virulence Determinants In Candida Flashcards

(55 cards)

1
Q

Give some examples where candida can outgrow

A

Antibiotics, pid/genetic defect, oestrogen/glycogen increase during pregnancy

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2
Q

What are the 4 stages of infection

A

Stage 1- colonisation through adhesion
Stage 2 - superficial infection: epithelial penetration and nutrient acquisition through host protein degradation

Stage3 - deep infection : penetrate tissues and vascular system and immune
evasion in blood

4- disseminated disease eg in organs like kidney via endothelial adhesion

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3
Q
  1. Adhesins

What are the main components of adhesins on outer cell wall

A

ligand binding domain (effector domain)

Then low complexity domain with ser/thr tandem repeats (often)

Can be anchored by gpi anchor to cell wall

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4
Q

What are the 3 families of adhesins in Candida albicans and what they bind (not in benign yeast)

A

Als family (9 genes) - epi and endothelium
Hwp1 family (5members) - saliva coated oral cavity and normal epi cells
Iff family (12 members)- epithelium

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5
Q

Looking at genome sequences (from previous lecture). What is evident about these family of genes

A

There is gene expansion/ duplication events - potentially with different affinity capacities like bspA in trichomonas

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6
Q

What agglutinin like gp are there in als family

A

Als 1 and 5

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7
Q

Explain their c terminus and the role it plays

A

C terminus is the low complexity ser/thr glycosylations allowing extension into environment

Threonine rich tandem repeat region forms amyloid like structure which has aggregation capacity (will aggregate with other fungi or bacteria esp in biofilms)

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8
Q

What is their n terminus/ effector domains like

A

Ig-like domains which swivel and act as a cavity for host peptides/ligands

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9
Q

Are they specific or broad binding

A

B-road s

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10
Q

Is it held by gpi anchor

A

Yes

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11
Q

Which adhesins important for biofilm formation on biotic / mucosal surfaces or abiotic like catheters

A

Als3 and hwp1

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12
Q

What are biofilms for

A

Evade immune system and increased resistance

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13
Q

Can they interact with other microbes

A

Yes bacterial-fungi interactions

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14
Q

What protein for drug resistance is upregulated in biofilms

A

Drug efflux pumps

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15
Q

Give a biofilm example in other candida species suggested important in Ibd (hoarau 2016)

A

C tropicalis with s marcescens and E. coli

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16
Q

What are invasins

A

Adhesins als3 and ssa1 which are specifically important for mediating fungal endocytosis for invasion eg for nutrient acquisition

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17
Q

What do they bind

A

E cadherin on epi or n cadherin on endothelial

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18
Q

What other way to invade is there

A

Penetration through hyphae

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19
Q

2 - morphogenesis

A
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20
Q

What sorts of things does morphogenesis occur to (pseudo with septation division or hyphae )

A

Ph (7 in blood = hyphae) and dfg16 alkaline example thewes 2007

, nutrients, co2 in blood, temperature (37c) , serum in blood

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21
Q

What is the diff between pseudo and hyphae

A

Pseudo have a construction at site of septation(between mother and daughter)

Cannot see distinct cells in hyphae and they are much thinner

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22
Q

What is filamentation crucial for

A

Access to blood for systemic
Escape from phagocytosis
Infection of internal organs - thewes found dfg16 for kidneys of mouse and pig

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23
Q

What happens when engulfed in phagosome

A

Hyphae switch occurs to kill them and escape

24
Q

What is the ras positive pathway of filamentation

A

Ras gtp active

Will activate adenylyl cyclase cdc35 to produce camp from atp

Camp activated pka will then phos tf efg1 which induces expression of ume6 hyphae specific gene

25
What is the mapk pathway/cph1 activation instead for ume6 expression
Mapk pathway activation by ras-gtp Ste11 mapkkk Hst7 mapkk Cek1 mapk will phosphorylate tf cph1 which also induced ume6 gene
26
What happens to double mutants of efg1 or cph1 (c4 suggests both mouse and zebra fish survival studies)
Form Budding avirulent forms
27
Which 2 proteins recruit tup1 txn repressor to block hyphae genes like ume6
Rfg1 and nrg1
28
What is the evidence dimorphism is required not just hyphae
Mutant tup1, rfg1 or nrg1 also reduces virulence of the fungi
29
Ume6 and virulence evidence study Using ume6 regulated under doxycycline (if dox present represses ume6) in mouse models injected with candida strains (engineered) What we’re the histologixal and survival results
After 30 days - 70% survival in dox+ / 0 Survivial when ume6 wasn’t repressed and was expressed highly in lack of dox presence Kidney histology showed lack of dox meaning ume6 exp allowed filamentation - showing it promotes virulence
30
What sorts of genes are hyphae specific/ upreg in hyphae form
Als3 (invasins and biofilms) saps and hwp1 (biofilm)
31
So how do we know it isn’t because of these genes not the actual shape causing virulence
Hgc1 (cell cycle protein) protein mutant which is involved in hyphae formation prevents shape change but had no effect on these genes eg hwp1 still high Still show reduced ability to colonise kidneys of mice / invasiveness and Reduced ability to kill the mice too (consistent with ume6 study)
32
How does quorum sensing (of both bacterial and fungal origin) affect hyphae growth aswell
Dense populations will release farnesol quorum molecule which will prevent hyphae formation for better colonisation of mucosal surfaces
33
How does farnesol block hyphae growth (showing potential importance of dense bacterial populations on inhibiting hyphal formation)
It acts to block adenyl cyclase cdc35 stopping camp activation of pka and efg1 tf
34
What 3 types of secreted enzymes do they have for nutrient acquisition, and tissue invasions - in candida are expressed on hyphal tip
Phospholipase (a,b,c,d classes) -only B are extracellular Secreted aspartyl proteinase (saps) Candidalysins
35
What 2 Phospholipase B class are shown as virulence factors on the tip of hyphae cells to breakdown cell membranes
Plb1 and 5
36
How many genes are there for saps (gene duplication example again) and the main differences
10 9+10 are cell surface gpi anchored Some are expressed in yeast to hyphae growth eg sap6 Some in yeast cells eg sap2 I.e more acidic ph than sap6 Can work at different ph Different substrates of proteins
37
How does internalisation of saps 2 and 6 cause apoptosis and inflam response characteristic of vaginal candidiasis
Activation of the nlrp3 inflammasome Caspases = apoptosis
38
Which highly expressed hyphae protein is processed into 8 peptides including candidalysin
Ece1
39
What does candidalysin toxin do
Forms pore within membrane causing permeability Also induced ap-1 tf c-Fos causing cytokines and chemokine exp for inflammation
40
Give an example of when this would happen
Inadequate NETs or phagocytosis
41
4- fitness traits
42
Give some fitness trait examples needed to survive a lot of environments
Evade host mechanisms eg ros/stress response Adequate nutrient acquisition/metabolic change Ph adaptation Metal acquisition
43
How is h202 formed at macrophage and neutrophils
NADPH oxidase complex forms and produces superoxide which is converted to h202
44
What does stress activated c.albicans hog1 kinase do in response to h202 (aswell as cap1 tf)
Upon stress (ox or osmotic) becomes phos and activated by h202 Translocation into nucleus Induces cell responses downstream crucial for survival (mutants are not able to survive under conditions of ox stress)
45
What other enzymes to detoxify ros do they have
Sod , tsa (thiol specific antioxidant) and sod5, catalase
46
Which tf is important for exp of all of these under ox stress and how
Cap1 When it becomes oxidised, the cys rich domains change conformation which mask it’s nuclear export sequence Starts to accumulate in the nucleus
47
Similar to hog1 mutants, what happens to cap1 mutants exposed to h202
Reduced survival / killer
48
What happens in wt hog1 vs mutant systemic mice modes Also what happens in macrophage modelling when both are knocked out
Hog1 Wt causes reduced survival in mice Compared to 100% survival in hog1 mutants = avirulent In macrophages with candida ko for both hog1 and cap1 there is a lack of filamentation and also reduced macrophage killing
49
Which human kinase similar to hog1 kinase suggests we could potentially use the inhibitors we have for cancer treatment for hog1 inhibition too - currently testing if it works
P38 kinase (inhibitors admin bc involved in tumour progression)
50
Which adhesin/invasin can steal fe from ferritin from host
Als3
51
What do they have to acquire zinc
Sincophore pra1
52
How is it suggested under starvation, cells can induce hyphae growth (for cell invasion/nutrient acquisition) through alkalinisation (dfg16 can induce this)
Production of ammonia from aa uptake by deamination = released and causes alkalinisation (Dfg16 mediated filamentation thewes 2007)
53
Although superficial infections like thrush and oral candidiasis are very common; what happens in systemic disease in Immunocompromised
Can overgrow/ colonise different organs like eye, brain, kidney and cause organ failure and death
54
How was pepstatin used to confirm that saps are virulence factors needed for tissue invasion
Injected candida with pepstatin sap inhibitor into mice Found reduced tissue invasion and reduced systemic candidiasis
55
Which protein present in the ecm of fungal biofilms which block neutrophil ros mediated killing
B glucans