1
Q
examples of fungi
A
- yeast
- mould
2
Q
describe fungi
A
- eukaryotic cells
- contain nuclei, mitochondria, etc.
3
Q
how do fungi exist
A
- as unicellular yeasts that divide asexually or
- as filamentous moulds that can divide sexually or asexually
4
Q
what’s something fungi have that eukaryotic cells don’t
A
a rigid cell wall
5
Q
describe the size of fungi
A
- bigger than bacteria
- smaller than blood cells
6
Q
what is fungi grown on
A
agar
7
Q
what are the cellular structures found in fungi
A
- cell wall
- cell membrane
- nucleus
- RER
- mitochondria
- vacuole
8
Q
does fungi have membrane bound or membrane free organelles
A
membrane bound
9
Q
what is the cell wall of fungi made of
A
polymers of glucans and mannans
10
Q
what is a fungi’s cell membrane rich of
A
sterols
11
Q
do antibiotics affect fungi
A
no, because different enzymes make the fungi’s cell wall and therefore the antibiotics can’t affect them the same way they do bacteria
12
Q
what is an important sterol for fungi
A
ergosterol
13
Q
what’s an important sterol for animal cells
A
cholestrol
14
Q
what’s the function of sterols
A
maintains membrane fluidity at a range of temperatures
15
Q
what’s significant about the different sterols found in animal cells vs fungi
A
when taking a drug for a fungal infection, it is able to target the fungi without harming the human
16
Q
example of drugs affecting sterols (binding)
A
- amphotericin B
- nystatin
17
Q
what do amphotericin B and nystatin do
A
- binds to ergosterol in the membrane and makes pores
- binds to cholestrol at a much lower affinity so we are not harmed
18
Q
example of drugs affecting sterols (biochemical pathway)
A
- imidazole and allylamine
- inhibit enzymes involved with the synthesis of ergosterol
- the incomplete membrane results in fungal cell death
19
Q
what are different antifungal agents
A
- polyenes
- candins
- azoles
- 5-fluorocytosines
20
Q
what do polyenes do
A
- make pores in the fungal cell membrane
- e.g. amphotericin B
21
Q
what do azoles do
A
- inhibit egosterol synthesis leading to cell death
- e.g. imidazole
22
Q
what do candins do
A
- inhibit cell wall synthesis leading to cell lysis
- “like penicillin for fungi”
23
Q
what do 5-fluorocytosins do
A
- a pro-drug: meaning it has no antifungal activity on its own but is converted into toxic compounds inside the fungal cell
- interfere with DNA, RNA, and protein synthesis
24
Q
how do 5-fluorocytosins work
A
1) 5-FC enters the fungal cell
2) once inside, cytosine deaminase converts it to 5-fluorouracil
3) it is converted further and is integrated into RNA
4) this results in faulty proteins, DNA and RNA
25
do 5-fluorocytosins affect us
no! because we don't have the cytosine deaminase enzyme
26
what do some yeasts produce (structural component)
a capsule
27
what's the function of a capsule for yeast
immune evasion
28
example of a yeast that produces a capsule
Cryptococcus neoformans
29
how do we find the capsule of a yeast under a microscope
1) stain the cell with ink
2) a "halo" forms around the cells, which doesn't stain as much (e.g. light pink against a purple stain)
3) this halo is the capsule - the ink does not penetrate the capsule
30
how do yeast grow
- by budding
- a daughter cell grows, attached to its mother
- once mature, the bud separates from the mother
- or, they can remain attached to the mother cell, leading to multiple outgrowths and a chain of connected cells
31
what's an important feature in yeast growth
- *some* yeast, e.g. candida albicans, grow germ tubes *under the right conditions*
- these germ tubes can develop into hyphae
32
what are the 2 ways in which yeast can grow
in dimorphic ways (has the ability to switch between two distinct shapes)
- via budding
- or via germ tubes which form hyphae like other fungi have
33
describe how candida albicans grows germ tubes
- produced within a couple hours of being put into a broth with serum in it
- ONLY candida albicans do this!
34
what's a good way to test for candida albicans from other yeasts
put it into serum broth for a couple hours and check for growth of germ tubes
35
what's a good way to test for Cryptococcus neoformans from other yeasts
- stain it with ink to check for presence of cell wall
- few other yeasts have one!
36
how do moulds grow
via hyphae
37
what are the 2 forms of hyphae
septated or aseptated
38
do mould grow asexually or sexually
both!
39
example of mould's asexual reproduction
conidia: asexual spores produced by moulds like aspergillus
40
example of mould's sexual reproduction
- ascospores: red sexual spores produced by Aspergillus nidulans
- sac-like structures
41
what is the core difference in sexual and asexual reproduction of moulds
- asexual: the offspring will be genetically alike
- sexual: the offspring will be genetically different
42
how do hyphae grow
via vegetative reproduction
43
what are the types of infections fungi can cause
- skin infections
- mucosal infections
- invasive infections
44
examples of skin infections caused by fungi
- ringworm
- tinea
45
examples of mucosal infections caused by fungi
thrush
46
examples of invasive infections caused by fungi
- sepsis
- meningitis
- pneumonia
47
describe skin infections caused by fungi
- superficial
- infect the skin, hair or nails
- living tissue is not invaded however a variety of pathological changes occurs (due to release of protease by fungi etc)
48
where can tinea infect an individual
- nails: onchomycosis
- feet: tinea pedis
- crotch: tinea cruris
- abdomen: tinea corporis
49
what are dermatophytes
group of fungi that cause skin infections
50
examples of dermatophytes
- microsporum
- trichophyton
- epidermophyton
51
how do you differentiate trichophyton from other dermatophytes
- has a red pigment on the bottom when grown on SD agar
- microscope: has very small (micro) conidia
52
how do you differentiate epidermophyton from other dermatophytes
- doesn't have a circular growth on agar: looks jagged
- microscope: has large (macro) conidia
53
how do you differentiate microsporum from other dermatophytes
- has a round colony on an SD agar plate
- microscope: has large (macro) conidia
54
what are the risk factors for skin infections by fungi
- high himidity, heat and perspiration
- diabetes and obesity
- friction from clothes
- contact with contaminated linen or towels
- contact with pets that have microsporum
55
how do we identify and diagnose skin infections caused by fungi
- itchiness
- appearance of skin
- skin scrapings from infected areas
- microsporum especially fluoresces under black light
56
how can skin infections caused by fungi be treated
- antifungal creams
- systemic treatment for severe cases or onychomycosis
57
what drug is typically used to treat skin infections caused by fungi
- imidazoles
- synthetic allylamines
(which block ergosterol synthesis = fungal cell lysis)
58
how do you prevent fungal skin infections
- avoid contact with agent
- dry between toes
- treat ringworm in pets
- avoid chaffing (friction of skin)
59
what are the types of thrush that can infect our body
- oral
- vulvovaginal or penile
- oesophageal
- other mucosal surfaces
60
what fungi causes thrush
- majorly candida albicans
- however other candida species are becoming more common
61
how does candida cause thrush
1) candida is normally a minor constituent of the mucosal flora
2) this can be changed if you come into contact with a candida carrier
3) generally this is fine, but our immune system can fail to suppress the candida growth or antibiotics can remove too much bacteria, allowing candida to grow
4) this results in high level colonisation, and therefore thrush
62
how can we test for the presence of candida for someone suspected with thrush
1) swab the infected area
- look at it under a microscope for characteristic features
- stain it to look for characteristic features
- grow it on agar
63
how can we treat oral thrush
-nystatin suspensions
- or imidazole creams and lozenges
64
what is vaginal thrush
- imidazole suppositories (medications designed for insertion into the vagina) and creams
- more common is a single dose treatment with fluconazole
65
example of fungi that cause systemic infections
- airborne aspergillus conidia
- mucosal candida
- cryptococcus basidospores
66
describe how aspergillus conidia causes disease
1) aspergillus conidia is frequently breathed in however our immune system manages it
2) immune suppression leads to aspergillus colonising the lungs
3) this lung infection can lead to penetration of lung tissue
4) this penetration enables the fungi to affect other organs now too
67
who is at risk of aspergillus infections
people with decrease immunosuppression due to:
- previous lung infections
- HIV/AIDS
- cancers
- transplant drugs
68
how do we diagnose aspergillus infections
take a biopsy and:
- view it under microscopy after staining to find hyphae
- culture it
- extract the gene and do PCR
- blood test to look for galactomannan (which is part of the aspergillus cell w all)
69
how can we test for aspergillus infections via galactomannan
1) sample of blood serum or sputum is taken.
2) antibodies that recognise galactomannan are added
3) if galactomannan is present, the antibodies bind to it
4) second antibody linked to an enzyme may then bind, creating a signal
5) when a substrate is added, the enzyme causes a colour change
6) the amount of colour change indicates whether galactomannan is present and roughly how much is present
70
how are aspergillus infections treated
via azole drugs, especially voricanazole
71
describe how mucosal candida causes systemic infection
- normally mucosal candida is dealt with by our immune system
- due to immune suppression, the candida can spread to blood then infect other organs
72
how can we identify and diagnose systemic infections caused by mucosal candida
take a biopsy:
- do microscopy
- grow in differential agar
- grow in blood agar
73
treatment options for systemic infections caused by mucosal candida
- main treatment is azoles like fluconazole
- echinocandin is used as an alternative
74
describe how cryptococcus basidospores cause disease
1) present in areas with high concentration of bird feces
2) normally dealt with by our immune system
3) due to immunosuppression, lung infection can occur when inhaled
4) cryptococcus can then enter the bloodstream and cross the blood-brain barrier and enter the meninges causing meningitis
75
symptoms of fungal meningitis
- fever
- bad headache
76
is bacterial or fungal meningitis more serious
bacterial
77
how can we identify and diagnose meningitis or lung infection by
1) take sputum if lung infection
2) take CSF if meningitis
3) microscopy or culture or enzyme immunoassay (using enzyme-linked antibodies) to identify the pathogen
78
example of an enzyme immunoassay test used to diagnose cryptococcus basidospores infection
rapid antigen test
79
example of an microscopy test used to diagnose cryptococcus basidospores infection
stain the sample and look for capsule around yeast cell
80
example of a culture test used to diagnose cryptococcus basidospores infection
- grow on niger seed agar
- differentiates into brown for melanin production (which cryptococcus produces)
81
primary treatments for cryptococcus basidospores infection
- amphotericin B
- 5-fluorocytosine
- synergistic combo
82
describe treatment of cryptococcus basidospores infection with amphotericin B
- inject into CSF
- however there can be toxicity issues after which it'll be discontinued
83
describe treatment of cryptococcus basidospores infection with 5-fluorocytosine
- oral or IV
- however there can be liver toxicity issues after which it'll be discontinued
84
describe treatment of cryptococcus basidospores infection with 5-fluorocytosine AND amphotericin B
amphotericin B enables 5-fluorocytosine to penetrate cells more deeply
85
what are alternative drugs for treating cryptococcus basidospores infection
- fluconazole
- echinocandin
medsci 202
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