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Microbiology and Immunology > Mycology > Flashcards

Mycology Flashcards

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Biology 101 flashcards
1
Q

How are fungi classified?

A

Unicellular (yeasts), filamentous (moulds), dimorphic

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2
Q

Unicellular fungi are

A

yeasts

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3
Q

Filamentous fungi are

A

moulds

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4
Q

Unicellular fungi are aerobes/anaerobes?

A

facultative anaerobes

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5
Q

Filamentous fungi are aerobes/anaerobes?

A

aerobes

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6
Q

Unicellular fungi/yeasts reproduce

A

asexually by budding

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7
Q

Filamentous fungi/moulds reproduce

A

by conidia (asexual spores)

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8
Q

On agar, unicellular fungi form _______ while filamentous fungi form _______

A

colonies (similar to bacteria); mycelia (do NOT look like colonies)

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9
Q

T/F yeasts are the same size as bacteria on gram stain

A

false; they are 2-3um whereas bacteria are 1-1.5um; ie yeasts are LARGER

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10
Q

Most fungi are _________ and live in ________

A

saprophytes (can live off organic matter) and live in soil or grow on organic material

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11
Q

Virulence of fungi (descending order)

A 
dimorphic
dermatophytes
agents of subcutaneous mycoses
opportunists
toxic fungi
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12
Q

What makes dimorphic fungi so virulent?

A

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

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13
Q

Dimorphic fungi have the capacity to

A

switch between unicellular and filamentous forms

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14
Q

Why are filamentous fungi not pathogenic?

A

They do not grow well at 37’ and they are aerobic; they may sometimes infect the skin

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15
Q

Histoplasma capsulatum is a ______ fungi that lives in ______ and causes what disease?

A

dimorphic (very virulent); caves; caves disease

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16
Q

Primary pathogenic fungi are

A

dimorphic and dermatophytes

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17
Q

T/F ringworm fungus is caused by a ringworm

A

False; caused by dermatophytes

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18
Q

Dermatophytes grow on __________ - why?

A

hair, skin, nails - they love keratin

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19
Q

T/F dermatophytes invade deeply

A

False

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20
Q

T/F Microsprum canis is a dermatophyte commonly found in dogs

A

False; more common in cats but affects both cats and dogs

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21
Q

Dermatophytes grow in which layer of skin?

A

Dead cells - keratin

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22
Q

T/F reaction to dermatophytes occurs in response to the growth of the fungi

A

False; it is the biproducts they release

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23
Q

Infection is caused by dermatophytes is called

A

tinea (not to be confused with the tapeworm taenia)

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24
Q

When taking a skin sample, what is preferential?

A

A skin scale from the edges where the fungi are growing

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25
Q

Tinea curis

A

tinea of the groin/jock itch

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26
Q

Tinea pedis

A

athletes foot

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27
Q

Tinea capitis

A

scalp

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28
Q

Tinea unguium

A

nails

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29
Q

Mycetoma (maduromycosis) commonly infects

A

feet

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30
Q

Mycetoma can be caused by

A

bacterium OR fungus

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31
Q

Bacterial cause of mycetoma (acintomycetoma) is

A

Nocardia spp

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32
Q

Fungal cause of mycetoma (eumycatoma) is

A

Madurella spp

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33
Q

What is characteristic of mycetoma?

A

sulfur granules

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34
Q

Actinomycetoma vs eumycetoma is distinguished by

A

diagnosis on sulfur granule samples

35
Q

Mycoses refers to

A

fungal infections

36
Q

Candidiasis is an example of what type of mycosis?

A

Opportunistic

37
Q

Candidiasis is caused by

A

Candida albicans

38
Q

How can antibacterial antibiotics eg ampicilin lead to vaginal thrush?

A

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

39
Q

Why do we react less to fungi (which allows more of them to grow before causing death)?

A

no PAMPs to induce cytokine response like with bacteria, therefore there can be much higher numbers of fungi than bacteria present

40
Q

Which form of cryptococcus is more virulent? neoformans or gattii?

A

gattii - causes cryptococcal/fungal meningitis in well people as well as IC (tf not necessarily an opportunistic pathogen)

41
Q

Fungal meningitis is most commonly caused by

A

Cryptococcus gattii

42
Q

_______________ is an AIDS-defining fungal illness

A

Cryptococcal meningitis

43
Q

Fungal meningitis is fatal if untreated because

A

it grows in the skull and raises ICP

44
Q

Like other common causes of meningitis, cryptococcus fungus has

A

a massive capsule

45
Q

On X-ray, what can be confused for lung cancer?

A

saphrophytic aspergillosis growing in a TB cavitation

46
Q

The worst form of aspergillosis is

A

systemic - occurs in immunocompromised patients eg little boy with leukaemia who had it in his brain

47
Q

T/F the type of fungal infection is able to be determined from a tissue slide sample

A

False; all fungi look the same in tissues

48
Q

How are fillamentous fungi differentiated?

A

By the conidia; fillamentous fungi do not produce conidia in tissues but may do so in a fungus ball (saprophytic)

49
Q

How are fungal infections diagnosed initially?

A

Microscopy

50
Q

The quick and dirty test for C. albicans involves

A

formation of germ tubes (pseudohyphae) in horse serum

51
Q

Other methods of fungal infection diagnosis

A

microscopy, culture, biochemical tests, Ag detection (latex agg), PCR, mass spec (MALDI-TOF like for bacteria)

52
Q

Ag detection is used commonly in which fungal infection?

A

Cryptococcus - capsular Ag can be detected in the CSF (same as for bacteria)

53
Q

What is the other application of Ag detection in fungal meningitis?

A

Montioring of treatment - titrating down the level of Ag to see if tx is working even though symptoms are not improving

54
Q

Systemic anti-fungal chemotherapies:

A

polyenes (amphotericin B)
triazoles (fluconazole, voriconazole)
echinocandins (capsofungin)
5-fluorocytosine

55
Q

Topical anti-fungal chemotherapy:

A

polyenes (nystatin)

imidazoles (clotrimazole)

56
Q

T/F Polyenes taken orally are not absorbed by the GIT

A

True

57
Q

When polyenes are used systemically they must be administered by ________ and are _________

A

injected; very toxic

58
Q

What are the targets of anti-fungals?

A

Ergosterol (cytoplasmic membrane)

Nucleic acids

59
Q

Which is the most important target of anti-fungals?

A

ergosterol in the cytoplasmic membrane

60
Q

Ergosterol is found in _________ and is akin to _________

A

fungal cytoplasmic membranes; cholesterol in human membranes

61
Q

Why are polyenes so toxic?

A

They bind to cholesterol in human cell membranes (less affinity than for ergosterol)

62
Q

Polyenes bind with high affinity to ________ and lower affinity to ________

A

ergosterol; cholesterol

63
Q

Polyenes have what affect on ergosterol?

A

Affect integrity of ergosterol and therefore the membrane

64
Q

What is critical about patients on polyene tx eg systemic amphotericin B?

A

they must be hospitalized to monitor toxicity of the polyene drug (binds human cholesterol as well as fungal ergosterol)

65
Q

Allylamines, triazoles, morpholines affect

A

synthesis of ergosterol

66
Q

T/F Using polyenes (amphotericin B) with allylamines, triazoles, morpholines etc. is antagonistic

A

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

67
Q

In serious fungal infection, ________ and ________ are often used together (ergosterol targeting drugs)

A

polyenes and triazoles

68
Q

5-fluorocytosine targets _______ and therefore affects synthesis of ___________

A

nucleic acids; DNA and RNA

69
Q

5-fluorocytosine is a ______ which is converted to ________

A

prodrug; 5-fluorouracil (5-FU)

70
Q

5-FU is also used as a drug in

A

cancer tx

71
Q

Cytosine deaminase is an enzyme found in

A

fungi but not humans

72
Q

What is the function of cytosine deaminase and therefore its use as an anti-fungal target?

A

activates the prodrug 5-fluorocytosine to 5-fluorouracil - therefore activation of the drug can only happen in yeasts

73
Q

The downside of 5-fluorocytosine as an anti-fungal tx is

A

that fungi readily become resistant

74
Q

Candida spp are tx with

A

fluconazole, amphotericin B, capsofungin

75
Q

Cryptococcus are tx with

A

amphotericin B + 5-fluorocytosine (5-FU)

76
Q

Aspergillus are tx with

A

Voriconazole, amphotericin B

77
Q

Dimorphic fungi are tx with

A

amphotericin B

78
Q

Why isn’t amphotericin B used for all fungal infections?

A

It is very effective but it is toxic

79
Q

Why are dermatophytoses NOT treated with amphotericin B?

A

they are not life-threatening infections

80
Q

Non-specific tx for dermatophytosis is

A

reducing fungal load

81
Q

Topical tx for dermatophytosis is

A

terbinafine (lamisil)
clotrimazole (canesten)
amorolfine (loceryl)

82
Q

Oral tx for dermatophytosis is

A

terbinafine
fluconazole
griseofulvin (most toxic)

83
Q

Oral anti-fungals are used

A

when it is difficult to tx topically OR infection is in the nails because they grow very slowly and drugs don’t penetrate the nail

Microbiology and Immunology (9 decks)

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