lecture 15) candida albicans fungal virulence factors case study

Question 1

what is the main species of candida that causes infection?

Answer 1

candida albicans

Question 2

what is virulence?

Answer 2

ability to cause disease

continuous variable

Question 3

what significantly impacts virulence?

Answer 3

host response

Question 4

what is meant by the term fully virulent?

Answer 4

average virulence, what you would expect the virulence of that specific species

Question 5

what does hypervirulent mean?

Answer 5

more virulent than what you would expect to see in that species

Question 6

what does attenuated/avirulent mean?

Answer 6

less virulent than what you would expect to see in that species

Question 7

why should you be careful with the term avirulent?

Answer 7

next to impossible to prove as may be virulent in a certain patient group

Question 8

virulence factors/traits are considered to be something that the pathogen has that damages the host. why is this not strictly true?

Answer 8

the host’s response is important

normally the host response to the pathogen that causes the damage

Question 9

what is the definition of disease from microbial attack “damage to the host”?

Answer 9

damage results from a range of host pathogen interactions

Question 10

describe the 2 cases in which disease would arise on the basis of pathogen - host immune system interaction

Answer 10

when the host response is too weak (impariment in host eg immunocompromised, direct action of pathogen might be to suppress immune response, release of toxin = damage due to microbial factors)

damage due to overreaction of host immune response (could still be killing the pathogen but the immune overreaction is causing damage to the host)

Question 11

what is the one thing to keep in mind about systemic infections of candida?

Answer 11

candida is always growing

Question 12

what happens in systemic infections of candida?

Answer 12

host response too low (immunocompromised)
new route of infection into sterile sites eg wound
due to growth of candida through the host

Question 13

what are superficial infections of candida due to?

Answer 13

low host immune response

Question 14

what genetic techniques are used for the identification of candida?

Answer 14

reverse and forward genetics

Question 15

what does reverse genetics involve?

Answer 15

sequence genome
look for proteins that may have a role in virulence (can compare proteins from other organisms that cause virulence)
expression based approach
infection model
genome wide expression analysis
see which ones are being switched on during virulence process

Question 16

what does forward genetics involve?

Answer 16

randomly mutagenise strain

screen for mutants and identify which ones cause disease

Question 17

why would forward genetics be tricky to carry out?

Answer 17

would have to make thousands of mutants (cant be tested in animals due to cost and ethics)

Question 18

what is the alternative to forward genetics?

Answer 18

signature tag mutagenesis

random mutants, tag them, put through a model and see which ones come out the other end as virulent factors

Question 19

how is the majority of work on candida carried out?

Answer 19

reverse genetics

Question 20

why cant you do random mutagenesis on candida?

Answer 20

obligate diploid
2 copies of each gene
too much damage would be done to DNA so would cause severe problems elsewhere

Question 21

how would you apply koch’s postulates to confirm a gene in an organism is important in causing disease?

Answer 21

mutate gene of interest
demonstrate the strain has attenuated virulence
complementation: reintroduce gene should cause virulence

Question 22

name the 4 stages of infection of candida albicans

Answer 22

adherence and colonisation
epithelial penetration
vascular dissemination
endothelial colonisation and penetration

Question 23

how do systemic disease of candida albicans spread?

Answer 23

spread through blood stream

has to grow and stay alive to cause disease

Question 24

what nutrient does candida albicans need in order to survive?

Answer 24

iron

Question 25

what makes candida albicans multifactorial?

Answer 25

continually growing

Question 26

name 5 virulence factors of fungal pathogens as the result of host-pathogen interaction

Answer 26

``` adhesion to host surfaces invasion of epithelial penetration beyond epithelia obtaining nutrients opposing host defences ```

Question 27

name 3 host defence mechanisms in virulent fungal pathogens as a result of host-pathogen interaction

Answer 27

flushing mechanisms molecular recognition phagocytosis and killing immune response

Question 28

describe the balancing acts between candida in the host for superficial infections

Answer 28

doesnt take much to tip the balance in favour of superficial infections

Question 29

describe the balancing act between candida and host in systemic infections

Answer 29

balance needs tipped further in the benefit of candida to cause systemic infection

Question 30

describe the asexual mating of candida

Answer 30

2 diploids mate forming a tetraploid | meiosis not identified, diploid forms due to chromosome loss

Question 31

what does polymorphic mean?

Answer 31

can exist in more than one morphology

Question 32

what does the CUG codon in candida mean?

Answer 32

they have a serine residue as opposed to a leucine residue makes working with candida very difficult as previous tools cant be used on candida as they would be inactive new tools had to be built from scratch to work with candida

Question 33

what are the 5 most common morphologies of candida albicans?

Answer 33

``` yeast pseudohyphae hyphae opaque chlamydospore ```

Question 34

how do yeast morphology of candida grow?

Answer 34

bud off each other | apical extension switching to isotropic growth

Question 35

how do filamentous morphology of candida grow?

Answer 35

``` occurs in certain environments elongated yeast cells stuck in apical extension for longer no cell separation so cells stay covalently bonded together can see where septation occurs ```

Question 36

how do hyphae morphology of candida grow?

Answer 36

grows out of apical extension branch forming network of filamentous switch from yeast to hyphae is very impotant in virulence

Question 37

how do opaque morphologies of candida grow?

Answer 37

budding elongated cells involved in candida mating (must grow as opaque) epigenetic switch requires chromosome to be lost to get heterozygosity at a locus so they can mate

Question 38

how do chlamydospore morphologies of candida grow?

Answer 38

response to environment branch off hyphal filament suspensor cell at the end of it you get chlamydospore

Question 39

what is hyphal growth promoted by?

Answer 39

``` temperature greater than 35 degrees C serum neutral pH high CO2/low O2 N or C starvation matrix embedded growth ```

Question 40

what is the most interesting morhphology switch and why?

Answer 40

yeast to hyphal | controlled by environment (serum and temperature)

Question 41

what factors are yeast growth promoted by?

Answer 41

acidic pH temperature less than 35C ammonium ion

Question 42

what morphology does candida grow in and when would this change?

Answer 42

grow as yeast when not starved | starvation: hyphal growth to move itself around to find food

Question 43

why does it make sense for candida to use hyphal morphology when starving?

Answer 43

isnt equal when it separates (apical cell gets most of cytoplasm, subapical extensively vacuolated)

Question 44

what does quorum sensing involve?

Answer 44

``` secrete QS molecule sense it respond to density high cell densities: promote yeast growth low cell density: promote hyphal growth ```

Question 45

what is the classic view of the role of hyphal morphogenesis in virulence?

Answer 45

hyphae: tissue penetration yeast: vascular dissemination

Question 46

what makes morphology important in virulence?

Answer 46

a certain morphology isnt superior to another | its the fact that candida can switch between morphologies that makes it virulent

Question 47

how do hyphae know when to burst through?

Answer 47

topism: hyphae can sense topography around them | sense weak point and push through the weak point

Question 48

what are the direct roles of hyphal morphogenesis in virulence?

Answer 48

invasion and tissue damage thigmotropism escape from phagocytes

Question 49

what are the indirect roles of hyphal morphogenesis in virulence?

Answer 49

genes co-regulated with morphogenesis

Question 50

what are the key components for the adhesion of candida and where are they found?

Answer 50

mannoproteins | outer layer of cell wall

Question 51

what are the 3 layers of the cell wall/membrane of candida albicans?

Answer 51

outer layer inner wall cell membrane

Question 52

what component is found in the inner wall of candida albicans that acts as a linking molecule?

Answer 52

beta-1,6-glucan

Question 53

what component is found just above the cell membrane of candida albicans that forms the skeleton?

Answer 53

beta-1,3-glucan aka chitin

Question 54

what is the ALS family?

Answer 54

agglutinin-like sequence family of cell wall proteins

Question 55

how many ALS members are there in candida albicans?

Answer 55

8: ALS 1-7, 9

Question 56

describe the structure of ALS family members

Answer 56

``` common structure signal peptide conserved domain tandem repeats anchor ```

Question 57

which ALS family member is especially important in adhesion?

Answer 57

ALS3

Question 58

what makes the ALS family adaptable?

Answer 58

if one is removed or isnt functioning anymore there are 7 others to take its place this stresses the importance of ALS otherwise it wouldnt have made all these other copies

Question 59

name the 2 main routes of invasion and penetration of candida albicans

Answer 59

induced endocytosis | active penetration

Question 60

how does candida albicans invade and penetrate the host via induced endocytosis?

Answer 60

adhere to cell and get cell to engulf it taken up into host passive process; fungus expresses invasin that interacts with the host cell surface interaction triggers fungal engulfment through endocytosis (zipper-like mechanism)

Question 61

how does candida albicans invade and penetrate the host via active penetration?

Answer 61

hyphae can push itself down and penetrate the host | directly into cells or between epithelial and endothelial cells

Question 62

although active penetration of invasion of candida albicans isnt well understood, what might it potentially involve?

Answer 62

physical force from apical growth turgor pressure secretes enzymes that breaks down proteins between cells holding them together use figmatopism to find way through

Question 63

what type of biofilm surfaces does candida albicans form?

Answer 63

biotic and abiotic surfaces

Question 64

where are the structured assemblies encased in biolfim formation of candida albicans?

Answer 64

extracellular matrix

Question 65

what do the biolfims formed by candida albicans display resistance to?

Answer 65

antifungals | host defences

Question 66

what impacts the formation of candida albican biofilms?

Answer 66

quorum sensing | polymicrobial interactions

Question 67

what are the 4 stages of biofilm formation of candida albicans?

Answer 67

attachment/adhesion of yeast cells to substrate initiation: formation of micro-colony maturation: hyphal development and ECM production dispersal: release of non-adherent yeast cells

Question 68

what are the biofilms of candida albicans surrounded by?

Answer 68

sticky mass

Question 69

what does candida albicans need to do in the host in order to survive?

Answer 69

it needs to acquire nutrients throughout infection cycle so it can grow

Question 70

what does candida albicans eat when in the host?

Answer 70

unfussy, gorbs itself on whatever it can find

Question 71

what metabolite suppression system do most microbes have that is more relaxed in candida albicans?

Answer 71

when there is glucose eat that first | candida use carbon sources simultaneously

Question 72

what makes it able to survive in phagocytic cells?

Answer 72

metabolically adaptable

Question 73

what does secretion of hydrolytic enzymes play a combined role in?

Answer 73

nutrient acquisition combat host defences adhesion

Question 74

what is meant by the term aspartic (proteinases)?

Answer 74

nutrient acquisition but degrades the host tissue

Question 75

why is the acquisition of iron important?

Answer 75

every living thing needs iron to live

Question 76

explain the reductive route candida albicans uses to exploit iron within the host

Answer 76

rip iron off host proteins reduces it oxidises it and takes up the oxidised form for use

Question 77

what is a siderophore?

Answer 77

a compound that a microbe releases that sequesters iron and then the microbes can take in this iron

Question 78

explain the siderophore route candida albicans uses to exploit iron from the host

Answer 78

candida doesnt produce siderophores but will use other microbes' siderophores

Question 79

why might the siderophore route of iron exploitation only be important in superficial infections of candida albicans?

Answer 79

in systemic infections there may not be any other microbes in the sterile environment that candida can make use of their siderophores

Question 80

explain the haemoglobin route that candida albicans uses for iron exploitation frrom the host

Answer 80

``` candida bonds and lyses RBCs haem released degraded/taken up into cell and degraded haem released uses this haem to rip iron from another haem group of the host ```

Question 81

what stress would be associated with phagocytosis?

Answer 81

change in pH low amino acid availability lack of glucose lack of iron

Question 82

what stress would be associated with respiratory burst?

Answer 82

reactive oxygen and nitrogen species

Question 83

what stress would be associated with cytokine burst?

Answer 83

inflammatory response | elevated temperatre

Question 84

how does candida avoid stressing agents in the phagolysosome?

Answer 84

candida has to acquire nutrients in the phagolysosome

Question 85

what is the pathogen response to stresses in the immune response?

Answer 85

immune evasion or pathogen response

Question 86

explain candida's response to thermal stress

Answer 86

as candida lives in us it is able to live up to 37 degrees celsius and a few degrees higher when we have a fever. therefore candidas response to thermal stress is slow and gradual

Question 87

explain candida's response to oxidative stress

Answer 87

expresses a range of things to detoxify the environment located on their surface rather than the cytoplasm like in other microbes if there is damage, it will recognise it and repair it

Question 88

what is most likely to get damaged from oxidative stress and why?

Answer 88

cell wall | this is the first part that the oxidate stress will hit