Flashcards in Mycology Deck (83):
How are fungi classified?
Unicellular (yeasts), filamentous (moulds), dimorphic
Unicellular fungi are
Filamentous fungi are
Unicellular fungi are aerobes/anaerobes?
Filamentous fungi are aerobes/anaerobes?
Unicellular fungi/yeasts reproduce
asexually by budding
Filamentous fungi/moulds reproduce
by conidia (asexual spores)
On agar, unicellular fungi form _______ while filamentous fungi form _______
colonies (similar to bacteria); mycelia (do NOT look like colonies)
T/F yeasts are the same size as bacteria on gram stain
false; they are 2-3um whereas bacteria are 1-1.5um; ie yeasts are LARGER
Most fungi are _________ and live in ________
saprophytes (can live off organic matter) and live in soil or grow on organic material
Virulence of fungi (descending order)
agents of subcutaneous mycoses
What makes dimorphic fungi so virulent?
They are best adapted to grow in human tissues because they can grow as filamentous fungi (non-pathogenic, do not grow well at 37') in the environment and then as yeasts 9grow well at 37') inside the body
Dimorphic fungi have the capacity to
switch between unicellular and filamentous forms
Why are filamentous fungi not pathogenic?
They do not grow well at 37' and they are aerobic; they may sometimes infect the skin
Histoplasma capsulatum is a ______ fungi that lives in ______ and causes what disease?
dimorphic (very virulent); caves; caves disease
Primary pathogenic fungi are
dimorphic and dermatophytes
T/F ringworm fungus is caused by a ringworm
False; caused by dermatophytes
Dermatophytes grow on __________ - why?
hair, skin, nails - they love keratin
T/F dermatophytes invade deeply
T/F Microsprum canis is a dermatophyte commonly found in dogs
False; more common in cats but affects both cats and dogs
Dermatophytes grow in which layer of skin?
Dead cells - keratin
T/F reaction to dermatophytes occurs in response to the growth of the fungi
False; it is the biproducts they release
Infection is caused by dermatophytes is called
tinea (not to be confused with the tapeworm taenia)
When taking a skin sample, what is preferential?
A skin scale from the edges where the fungi are growing
tinea of the groin/jock itch
Mycetoma (maduromycosis) commonly infects
Mycetoma can be caused by
bacterium OR fungus
Bacterial cause of mycetoma (acintomycetoma) is
Fungal cause of mycetoma (eumycatoma) is
What is characteristic of mycetoma?
Actinomycetoma vs eumycetoma is distinguished by
diagnosis on sulfur granule samples
Mycoses refers to
Candidiasis is an example of what type of mycosis?
Candidiasis is caused by
How can antibacterial antibiotics eg ampicilin lead to vaginal thrush?
normally lactobacilli produce lactic acid to keep the vaginal pH low which fungi do not like; after AB Tx for an infection it will suppress these lactobacilli and raise the pH of the vagina predisposing to infection by candida fungi already present
Why do we react less to fungi (which allows more of them to grow before causing death)?
no PAMPs to induce cytokine response like with bacteria, therefore there can be much higher numbers of fungi than bacteria present
Which form of cryptococcus is more virulent? neoformans or gattii?
gattii - causes cryptococcal/fungal meningitis in well people as well as IC (tf not necessarily an opportunistic pathogen)
Fungal meningitis is most commonly caused by
_______________ is an AIDS-defining fungal illness
Fungal meningitis is fatal if untreated because
it grows in the skull and raises ICP
Like other common causes of meningitis, cryptococcus fungus has
a massive capsule
On X-ray, what can be confused for lung cancer?
saphrophytic aspergillosis growing in a TB cavitation
The worst form of aspergillosis is
systemic - occurs in immunocompromised patients eg little boy with leukaemia who had it in his brain
T/F the type of fungal infection is able to be determined from a tissue slide sample
False; all fungi look the same in tissues
How are fillamentous fungi differentiated?
By the conidia; fillamentous fungi do not produce conidia in tissues but may do so in a fungus ball (saprophytic)
How are fungal infections diagnosed initially?
The quick and dirty test for C. albicans involves
formation of germ tubes (pseudohyphae) in horse serum
Other methods of fungal infection diagnosis
microscopy, culture, biochemical tests, Ag detection (latex agg), PCR, mass spec (MALDI-TOF like for bacteria)
Ag detection is used commonly in which fungal infection?
Cryptococcus - capsular Ag can be detected in the CSF (same as for bacteria)
What is the other application of Ag detection in fungal meningitis?
Montioring of treatment - titrating down the level of Ag to see if tx is working even though symptoms are not improving
Systemic anti-fungal chemotherapies:
polyenes (amphotericin B)
triazoles (fluconazole, voriconazole)
Topical anti-fungal chemotherapy:
T/F Polyenes taken orally are not absorbed by the GIT
When polyenes are used systemically they must be administered by ________ and are _________
injected; very toxic
What are the targets of anti-fungals?
Ergosterol (cytoplasmic membrane)
Which is the most important target of anti-fungals?
ergosterol in the cytoplasmic membrane
Ergosterol is found in _________ and is akin to _________
fungal cytoplasmic membranes; cholesterol in human membranes
Why are polyenes so toxic?
They bind to cholesterol in human cell membranes (less affinity than for ergosterol)
Polyenes bind with high affinity to ________ and lower affinity to ________
Polyenes have what affect on ergosterol?
Affect integrity of ergosterol and therefore the membrane
What is critical about patients on polyene tx eg systemic amphotericin B?
they must be hospitalized to monitor toxicity of the polyene drug (binds human cholesterol as well as fungal ergosterol)
Allylamines, triazoles, morpholines affect
synthesis of ergosterol
T/F Using polyenes (amphotericin B) with allylamines, triazoles, morpholines etc. is antagonistic
False; while polyenes target integrity (bind to ergosterol) and the others affect the synthesis they seem as though they should act antagonistically but they are in fact often used together as there is no evidence of antagonism in the clinic
In serious fungal infection, ________ and ________ are often used together (ergosterol targeting drugs)
polyenes and triazoles
5-fluorocytosine targets _______ and therefore affects synthesis of ___________
nucleic acids; DNA and RNA
5-fluorocytosine is a ______ which is converted to ________
prodrug; 5-fluorouracil (5-FU)
5-FU is also used as a drug in
Cytosine deaminase is an enzyme found in
fungi but not humans
What is the function of cytosine deaminase and therefore its use as an anti-fungal target?
activates the prodrug 5-fluorocytosine to 5-fluorouracil - therefore activation of the drug can only happen in yeasts
The downside of 5-fluorocytosine as an anti-fungal tx is
that fungi readily become resistant
Candida spp are tx with
fluconazole, amphotericin B, capsofungin
Cryptococcus are tx with
amphotericin B + 5-fluorocytosine (5-FU)
Aspergillus are tx with
Voriconazole, amphotericin B
Dimorphic fungi are tx with
Why isn't amphotericin B used for all fungal infections?
It is very effective but it is toxic
Why are dermatophytoses NOT treated with amphotericin B?
they are not life-threatening infections
Non-specific tx for dermatophytosis is
reducing fungal load
Topical tx for dermatophytosis is
Oral tx for dermatophytosis is
griseofulvin (most toxic)