Lecture 9 - Intro to mycology Flashcards
what is mycology?
study of fungi
what are fungi?
yeasts and moulds, eukaryotic cells that can either be unicellular yeasts or filamentous moulds
unicellular yeasts divide?
asexually
filamentous moulds divide?
either sexually or asexually
what is different about yeast and fungi cell walls? in comparison to ours
rigid cell wall
true or false, yeast are bigger than a bacteria but smaller than a neutrophil
true
true or false, yeasts and moulds can grow on agar
true
true or false, yeasts and moulds contain membrane bound organelles?
true
which membrane bound organelles do yeasts and moulds contain?
80s eukaryotic ribosome
what is different about the cell membrane of fungi?
rich in sterols
what makes up the cell wall of yeasts and moulds
polymer of glucans, mannans
- so penicillin wont work against yeasts and moulds
what is ergosterol
a cell membrane sterol which maintains fluidity of membrane (the yeast and fungi version of cholesterol)
what drugs target ergosterol and how does it kill the cell?
Amphotericin B and Nystatin bind ergosterol and form pores in the membrane
Imidazole and allylamine drugs inhibits enzymes in ergosterol synthesis
what are the sites of action of anti-fungal agents?
- ergosterol in the membrane
- enzymes forming ergosterol
- glucan cell wall polymer
- cytosine deaminase
antibiotics that target unique features of bacteria…?
do not work on fungi
how do candins work?
inhibit cell wall synthesis of yeasts and moulds by inhbiting
how does 5-fluorocytosine work?
inhibits cytosine deaminase involved in DNA and RNA synthesis, leading to cell death
true or false, humans contain cytosine deaminase
false
what yeast produces a capsule?
cryptococcus neoformus
how do yeasts grow?
by budding
what are germ tubes aka?
germ tubes are unique to?
candida albicans
how are germ tubes produced
C. albicans produce a germ tube within 2 hours of being in a liquid broth
what are the main properties of yeasts?
- budding daughter cell
- cell wall with mannan and glucan polymers
- vacuole
by which process do yeasts do asexual reproduction?
binary fission
what are conidia?
spores produced asexually by fungi at the tip of a hypha
what are ascospores?
sexually produced fungal spores
what types of diseases are caused by yeasts and moulds?
skin infections
mucosal infections
invasive infections
what are dermatophytes?
yeasts or moulds that cause skin infections
what are cutaneous mycoses?
superficial fungal infections of the skin, hair or nails. no living tissue is invaded, but a variety of pathological changes occur
cutaneous mycoses produce a range of _________
proteases
what are examples of skin diseases cause by cutaneous mycoses?
tinea pedis (foot)
tinea cruris (crotch)
tinea corporis (abdomen)
onychomycosis (toenails)
ringworm (not a worm, but a fungus)
what are the three species of dermatophytes?
microsporum
trichophyton
epidermiphyton
how can we identify trichophyton rubrum?
a fungus that has a red pigment on reverse when done on sabourad agar
- can see microconidia under microscopy
how can we identify epidermophyton floccosum?
has more of a dendritic growth on the agar
- microscopy shows macroconidia
how can we identify microsporum canis?
round growth of mould
- microscopy shows macroconidia
what are the main sources of infection of Trichophyton rubrum and epidermophyton floccosum?
they are anthropophillic, so they prefer humans. spread is through contact e.g towels, showers, clothing
what is the main source of infection for microsporum canis
cats and dogs
what are the risk factors for fungal skin infections?
high humidity, heat and perspiration
diabetes and obesity (skin folds)
friction from clothes
contact with contaminated clothing or towels
(fungi gets in through break in the skin)
how can we identify and diagnose fungal skin infections?
symptoms: itchiness and distinctive appearance
microscopy and growth from hairs and skin scrapings from infected areas
may fluoresce under black light (microsporum and ringoworm)
how do we treat fungal skin infections
anti fungal creams
systemic treatment for severe cases or for onychomycosis
what antifungal chemicals are used against fungal skin infections, and what mechanism do they use to kill fungi?
Imidazoles and synthetic allylamines
- both act to block ergesterol synthesis and cause cell lysis
what are the prevention options for fungal skin infections?
avoid contact
dry between toes
treat ringworm in pets and avoid contact
avoid or prevent chaffing (entry point of fungi)
what is the main mucosal fungal infection?
thrush or candidiasis
where can candidiasis occur?
- orally
- vaginally and penile
- oesophageal
- other mucosal surfaces
true or false, candida albicans is the only yeast that causes thrush/candidiasis
false, other candida species are becoming more common
is candida a constituent of the mucosal flora?
yes, in low amounts
how can thrush/candidiasis occur?
AB treatment
immunosuppression
contact with infected person
what are the treatment options for oral candidiasis?
nystatin suspensions, imidazole creams and lozenges
what are the treatment options for vaginal candidiasis?
imidazole suppositories/pessaries and creams
- single dose oral treatment with fluconazole which has proven effective in 95% of cases
what causes severe fungal infections?
aspergillus conidia, and we breathe them in all the time, it comes from soil. but is normally dealt with by competent immune defences in the lungs
what causes aspergillus conidia to become a more severe infection?
immunosuppression of the lungs or a previous lung infection
- hematogenous spread if there is penetration of the lung tissue, other organs infected
how can we identify presence of aspergillus conidia infection?
using biopsy methods:
- microscopy
- culture
- PCR
- galactomannan EIA (antibody attaching to pathogen in A.C)
what treatments are most effective against aspergillus conidia?
- IV voriconazole is the most effective treatment
how can mucosal candida get more severe, and how can we identify it?
immunosupression causes increased severity
- break in mucosal barrier leads to hematogenous spread and infection of other organs
- biopsy options are microscopy and culture
describe amphotericin B as a treatment option for candidiasis
not commonly used especially due to toxicity issues.
describe fluconazole as a treatment option for candidiasis
mainstay treatment
not for patients receiving azole drug prophylaxis
describe echinocandin as a treatment option for candidiasis
it inhibits synthesis of beta glucan chains in the cell wall. used as an alternative to fluconazole.
what is the most common source of cryptococcus?
basidospores in pigeon poo
what causes cryptococcus to become a more severe infection?
immunosuppression eg HIV/AIDS
- lung infection, can lead to hematogenous spread and cause meningitis (characterised by fever, bad headache)
how can we identify an infection of cryptococcus?
EIA (like a rapid antigen test)
microscopy
Culture
sample is either sputum (if lung infection) or CSF (if meningitis is suspected)
how can we tell from microscopy alone whether or not we have cryptococcus fungal infection?
Cryptococcus neoformans is pretty much the only yeast/fungus with a capsule
how can we tell if there is cryptococcus infection causing meningitis by the culture?
CSF culture on niger seed agar. If cryptococcus is present, melanin will be produced and will produce a brown colour
describe Amphotericin B as a treatment for cryptococcus
intrathecal injection, may be discontinued if toxicity issues
describe 5 fluorocytosine as a treatment for cryptococcus
administered orally or via IV.
inhibitor of DNA and RNA synthesis
may be discontinues if live toxicity
describe the synergistic combination as a treatment for cryptococcus
- taking amphotericin and fluorocytosine to penetrate cells more easily
- may need lower concentrations (yay less toxicity)
what are the two alternative treatments for cryptococcus, other than amphotericin B and fluorocytosine?
Fluconazole
echinocandin
